https://orcid.org/0009-0000-0581-3164
Figures
Abstract
The genus Commicarpus Standl. is a member of the family Nyctaginaceae. The genus includes about 30–35 species distributed across tropical and subtropical regions worldwide, including Saudi Arabia. Five species of Commicarpus are found through, the field survey, which are primarily concentrated in the western and southwestern regions of Saudi Arabia. The collected species are C. grandiflorus, C. helenae, C. mistus, C. plumbagineus, and C. sinuatus. The aim of this study is to do morphological, anatomical, and palynological analyses of these species. Morphologically, growth habit, stem texture, leaf characteristics, floral structure, and fruit morphology were evaluated, these characters are significant to distinguish Commicarpus species. Anatomical studies of the stems, leaves, and petioles show some important characteristics that can help to separate Commicarpus species, including variations in collenchyma and chlorenchyma layers, vascular bundle arrangement, and mesophyll structure. Petiole anatomy, particularly the shape and arrangement of ground tissue and vascular bundles, provides additional taxonomic markers. Also, the study of pollen grains of the species using light microscopes (LM) and scanning electron microscopes (SEM) provides significant character that can be used for species differentiation, including differences in pollen size, shape, polar and equatorial axis dimensions, tubuliferous density, pore diameter, and spinule length. Pollen grains are very large in C. grandiflorus, C. plumbagineus, and C. sinuatus and large in C. helenae and C. mistus; their shapes range from oblate-spheroidal in C. grandiflorus to prolate-spheroidal in the other species. Two keys are constructed, one utilizing morphological characteristics and the other employing anatomical features of the petioles to aid in species identification. These results contribute valuable taxonomic information for the genus Commicarpus in Saudi Arabia.
Citation: Ytemi MS, Alsamadany H, Al-Ghamdi FA, Mashlawi AM, El-Shabasy A (2026) Taxonomic characterizations of the genus Commicarpus Standl. (Nyctaginaceae) in Saudi Arabia. PLoS One 21(5): e0350149. https://doi.org/10.1371/journal.pone.0350149
Editor: Rongchun Han, Anhui University of Chinese Medicine, CHINA
Received: October 23, 2025; Accepted: May 8, 2026; Published: May 28, 2026
Copyright: © 2026 Ytemi et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: All relevant data are within the manuscript.
Funding: The author(s) received no specific funding for this work.
Competing interests: The authors have declared that no competing interests exist.
Introduction
A large part of the Arabian Peninsula is made up of Saudi Arabia, a vast arid desert covering over 225,000 square kilometers. It is frequently thought of being a nation with mostly desolate terrain and little greenery [1]. With the exception of mosses and grasses, a research by Collenette (1999) [2] revealed an astounding biodiversity of 2,250 plant species. over 855 genera and 2,282 species from 131 families make up this varied flora. The northwestern and southwestern regions have the highest concentration of plant species, making up over 70% of the country’s floral diversity. According to current estimates, there are around 1,620 (71.02%) herbaceous plants, 565 (24.73%) shrubs, and 97 (4.25%) trees in Saudi Arabia [3].
The Nyctaginaceae Jussieu is a compact family comprising approximately 30 genera and 400 species [4]. It is often referred to as the Four-O’Clock family due to the characteristic of many species having flowers that bloom from late afternoon to early evening [5]. The Nyctaginaceae family is primarily found in tropical and subtropical regions of the New World [6,7], particularly the Americas [8], with some genera also extending into temperate areas such as southern Africa, Western Asia, East Asia, and Australia [4,9–13]. The family has two main centers of distribution in the Americas: tropical and subtropical South America and the Antilles, as well as the southwestern United States and northern Mexico in North America [6]. However, certain genera like Boerhavia, Commicarpus, Pisonia, and Mirabilis are found in the Old World, specifically in South Africa, with Phaeoptilum being restricted to Africa [4].
Commicarpus Standl. is a genus within the Nyctaginaceae family, alongside other genera like Boerhavia L., Mirabilis L. and Pisonia L. and This genus comprises approximately 30–35 species native to tropical and subtropical regions, with a significant presence in Africa and western Asia [6,14]. Commicarpus species are characterized by unique anthocarp details, flower morphology, and growth preferences in calcium-rich soil with heavy metal components [4,15]. The genus Commicarpus standl. is widely distributed across tropical and subtropical regions, with a notable presence in Africa, Western Asia, East Asia, Australia, and the Americas 2, 6, 8, 9,10, 11, 12, 13, 14, 16]. Within the Kingdom of Saudi Arabia, this genus has estimates ranging from 3 to 7 species [2,9,11,13,16]. These species are primarily concentrated in the western and southwestern regions of Saudi Arabia.
Struwig et al. (2011) [17,18] studied the anatomy of Boerhavia and Commicarpus species from the Nyctaginaceae family in southern Africa, investigating how these plants have adapted anatomically to live in Namibia’s arid environments. A systematic revision of Commicarpus species in South Africa was carried out by Struwig & Siebert (2013) [15], most likely comprising the identification, categorization, and description of species in this genus. Pakravan et al. (2023) [19] used a variety of methods, including morphological investigations, to conduct a systematic investigation of Nyctaginaceae species in Iran. In order to identify species within the Nyctaginaceae family in Iran, they focused on finding important traits. The shapes, sizes, and arrangements of leaves, stems, flowers, and other exterior aspects were among the general physical characteristics and plant structures that they looked at. Additionally, the anatomical study investigated differences in vascular bundles, petioles, phloem, xylem, stomatal types, and epidermal cells in the internal structures and tissues of Iranian Nyctaginaceae plants. In order to classify plants taxonomically and comprehend their ecological responsibilities, this kind of anatomical investigation offers insights into the physiological processes and adaptations of the plants. Struwig et al. (2013) [20] examined the pollen morphology of southern African species of Boerhavia and Commicarpus, probably in an effort to comprehend the properties of pollen grains and their possible importance in plant identification and evolutionary research. The distinctive characteristics and morphology of the pollen grains of the Nyctaginaceae species in Iran were described by Pakravan et al. (2023) [19]. This palynological approach can offer further evidence to support the taxonomic location and connections within the Nyctaginaceae family since pollen grains have unique sizes, shapes, and surface patterns that can be utilized to distinguish between species.
Despite slight variations in habit and leaf shape, Meikle, (1978) [21] noted that all Commicarpus species are superficially similar in growth form and foliage, making it challenging to distinguish them in the field. This raises the question of how to reliably differentiate between Commicarpus species based on observable characteristics. There is inconsistency in the species of the genus Commicarpus recorded in the references of the Flora of Saudi Arabia and Arabian Peninsula. This discrepancy highlights the need for clarification and standardization of the species composition within the genus in the region.
The aim of this study is to evaluate the taxonomic value of Commicarpus species; C. grandiflorus (A.Rich.) Standl., C. helenae (Schult.) Meikle, C. mistus Thulin, C. plumbagineus (Cav.) Standl., and C. sinuatus Meikle within Saudi Arabia based on morphological, anatomical, and palynological characterizations.
Materials and methods
Specimen collection for morphological studies
The studied area is extended north from Al-Madinah Al-Munawwarah and Makkah Al-Mukarramah, then downwards into the southwestern regions at Asir and Jazan. In the present study, samples of Commicarpus species were collected from various regions of Saudi Arabia (Table 1 and Fig 1), as referenced in the Flora of Saudi Arabia and Arabian Peninsula, documented by [2,9,11,13,16]. These sources provide evidence that these species exhibit a predominant distribution in the western and southwestern regions of Saudi Arabia. The collection specimens through 2023 were carefully preserved as herbarium specimens [22] and stored at the King Abdul-Aziz University herbarium (Fig 2). To enhance reproducibility, all specimens were geo-referenced using GPS coordinates, and detailed collection metadata—including habitat type, altitude, and sampling date—were systematically recorded following standardized biodiversity sampling practices.
The map is designed according to USGS National Map Viewer (public domain): http://viewer.nationalmap.gov/viewer/. The Gateway to Astronaut Photography of Earth (public domain): http://eol.jsc.nasa.gov/sseop/clickmap/.
Herbarium specimens of the studied species; (a) C. grandiflorus; (b) C. helenae; (c) C. mistus; (d) C. plumbagineus; (e) C. sinuatus.
Subsequently, measurements and observations of 100 replicas for each species were conducted to record various vegetative characteristics, including leaf features such as length, petiole length, arrangement, lamina shape, length, width, apex, base shape and margin structure. Also, these reproduction Commicarpus species were observed: inflorescence type, length, hair characteristics and surface texture, as well as flower attributes including length, pedicel length, petaloid region length, coriaceous length, perigonium shape and color, stamens number and length, ovary and stigma shape, number of ovules, and the presence or absence of bracts. Additionally, fruit shape, length, and indumentum were documented. All measurements were performed using calibrated digital calipers, and replicate measurements were averaged to minimize observational error and improve data reliability.
Anatomical preparations
Fresh samples of stem, leaf, and petiole were collected from various locations in Saudi Arabia during 2023. Utilizing preparations of [23–25], the specimens were collected and prepared for cross-sectional permanent slides. The plant parts (stem, leaf, and petiole) were fixed in a fixative solution consisting of 50 ml absolute ethyl alcohol, 10 ml concentrated formalin, 5 ml glacial acetic acid, and 35 ml distilled water [23]. After appropriate fixation time, the preserved samples were cut into small pieces (0.5 cm) using a sharp scalpel and passed through a graded series of ethyl alcohol (30%, 50%, 70%, 80%, 90%, 95%, and absolute alcohol) for one hour at each concentration [24]. The samples were passed through a series of ethyl alcohol-xylene mixtures in the following volume ratios: 3:1, 1:1, and 1:3. Then, they were placed in pure xylene for two hours. Samples were transferred from xylene (after clearing) to a 1:1 mixture of xylene and liquid paraffin and left in the oven at 60°C overnight to replace the evaporated xylene with liquid paraffin. The liquid paraffin-xylene mixture was poured out and replaced with pure liquid paraffin, and the samples were left in the oven for two hours. The samples were then immersed in wax overnight to ensure proper impregnation. For embedding and trimming, the plant parts were positioned inside aluminum corner molds covering with amount of liquid paraffin, then labeled and left cool at lab temperature. The wax cubes containing the plant parts were then placed in the freezer until they were fully hardened and ready for trimming [26]. The cubes (containing the plant parts) were trimmed using a special blade and placed on a microtome. The samples were cut into 12-micron-thick sections for stem, leaf, and petiole in the form of paraffin ribbons. These ribbons were placed in a water bath at 40°C to flatten them. The ribbons were lifted using clean glass slides precoated with a thin smear of glycerin-albumin adhesive. The slides were tilted slightly to remove water and then placed on a hot plate (35–40°C) for 4–12 hours to fix the section ribbons and remove wrinkles. The slides were then ready for dewaxing and staining. Paraffin wax was removed from both inside and outside the tissue by placing the slides containing the sections in the oven to melt the wax thoroughly. The glass slides were then passed through xylene and ethyl alcohol concentrations as follows: 100% pure xylene, 3:1 xylene and ethyl alcohol for five minutes, 1:1 xylene and ethyl alcohol for five minutes, and 1:3 xylene and ethyl alcohol for five minutes. Subsequently, the slides were passed through a descending series of ethyl alcohols (100, 95, 90, 80, 70, 50, 30) for 5 minutes at each concentration. The slides were then stained with safranin (1% w/v dissolved in 50% ethanol) and fast green (0.5% w/v dissolved in 95% ethanol) stains and examined. Staining quality and section integrity were verified microscopically prior to imaging to ensure accurate tissue differentiation and to minimize preparation artifacts. The prepared slides were examined and documented using standard light microscopy techniques [27].
Palynological studies
In the current study, pollen from fresh plant material collected in Saudi Arabia was examined using light microscopy (LM) and scanning electron microscopy (SEM) to analyze its morphology and ultrastructure. The pollen was prepared using the acetolysis method according to [28]. The acetolysis method was applied to ensure consistency. The procedure was conducted under controlled conditions to preserve exine structure while effectively removing cytoplasmic material, which is essential for accurate palynological analysis. Flowers containing mature anthers were collected, and the anthers were separated using fine forceps and a dissecting needle. The isolated anthers were transferred onto Pollen materials of each species were removed from the anthers of well-developed flower buds near to anthesis in a Petri dish and placed in a centrifuge tube with 5 mL acetic acid, then remaining for at least 24 hours before acetolysis. Centrifuge was done at 1500–1800 revolutions per minute/rpm for 5–10 min and the supernatant was decanted then 4.5 mL of acetic anhydride and 0.5 mL of sulfuric acid (9:1) were placed in the centrifuge tube. Immediately the centrifuge tubes were dipped with the acetolysis mixture into a beaker containing hot water in a laboratory water bath close to boiling from 80 to 100 ° C. Subsequently a glass rod in each tube was placed and gently mixed the contents at regular intervals. The water bath was kept boiling slowly for 1–2 min then the bath must be placed in a fume hood to avoid nasal aspiration of vapors, which are very irritating and toxic. After that centrifuge was done for five minutes at 1500–1800 rpm then the supernatant was discarded. Distilled water was added to the pollen residue to make up the volume to 10 ml. Each tube was shaken with one by one the two drops of ethyl alcohol. After centrifugation and decantation, a mixture of 5 ml of water with glycerin in equal parts was added to pollen residues. Let it remain in this solution for half an hour or until the next day. Finally, a cube of glycerin gelatin about 1 mm3 that was inserted into the bottom of the centrifuge tube to collect the pollen residue to be placed in the center of the microscope slide and gelatin melting process is performed carefully under heat to avoid boiling. The coverslip was placed in the center of the slide and sealed with paraffin and examined under a light microscope. The prepared slides were examined using an Olympus light microscope equipped with an oil immersion lens. A total of 10–20 pollen grains from each species were analyzed. Measurements included the equatorial axis diameter, the polar axis length, spinule length, and pore diameter, all recorded using a calibrated ocular micrometer. For SEM, pollen grains were released from the anther samples and fixed on stubs using double-sided adhesive tape; the samples were then coated with a 150-angstrom-thick layer of gold and examined using a Jeol JEM 5400 LV SEM. Palynological descriptions follow the terminology established by [29]. Imaging parameters and coating thickness were standardized to ensure comparability of surface ornamentation and to minimize imaging bias.
Scoring data and statistical analysis
To establish a phenetic analysis, every morphological and anatomical characteristic of the species under study was assessed. The Pclass approach was used to build the similarity matrix and cluster analysis. The distances were calculated based on the Gower coefficient. The pairwise similarities and dissimimilarites between the operational taxonomic units (OTUs) were determined using the Nei genetic similarity index (SI) and the equation SI = 2Nij/ (Ni + Nj), where Ni and Nj represent the total number of comparative characters for each species i and j, respectively, and Nij represents the number of common characters shared between them. The phenogram was generated using a sequential agglomerative hierarchical nested clustering approach. This method, known as unweight pair group mathematical averages (UPGMA), involved combining previously studied fern species with similar characteristics through a series of successive mergers [25]. The Pearson correlation coefficient was used among morphological vs anatomical parameters, morphological vs palynological parameters finally anatomical vs palynological parameters in representation of simple linear regression (SRL) to estimate the degree of affinity between each characteristic parameters and determine the compatibility level that influenced on Commicarpus species by using methods according to [30–32]. P values, which were employed as significant parameters, were determined by applying [33] techniques based on the degree of freedom. All statistical analyses were conducted using standardized multivariate approaches to ensure robustness and reproducibility.
Species synopsis
The species synopsis includes a taxonomic treatment of the genus Commicarpus Standl., which encompasses a description of the studied species within this genus in Saudi Arabia. It also involves the development of a detailed taxonomic key to facilitate species identification based on distinctive morphological, and anatomical characteristics. This work aims to resolve taxonomic ambiguities and enhance the understanding of Commicarpus diversity within Saudi Arabia.
Results
Morphological analysis
Stem morphology (Fig 3 and Table 2).
The analysis of stem morphology in Commicarpus species from Saudi Arabia revealed distinct growth forms and notable variations in stem characteristics across the five studied taxa.
All examined species exhibit a perennial herbaceous habit with variations in woody development. Commicarpus grandiflorus and C. plumbagineus are characterized as soft woody, whereas C. helenae, C. mistus and C. sinuatus display a woody-based structure. Branching patterns range from slightly branched to much branched forms. Commicarpus grandiflorus, C. mistus and C. plumbagineus exhibit a slightly branched structure, contributing to their more linear growth habits. In contrast, C. helenae and C. sinuatus are highly branched, leading to a more complex and expansive growth form. The orientation of growth further differentiates the species: C. grandiflorus displays an accumbent or ascending habit, C. helenae grows suberect to scrambling, C. mistus maintains an erect posture, C. plumbagineus exhibits scandent or trailing behavior, and C. sinuatus is characterized by a tangled growth pattern.
Significant variation in stem length was observed among the species. C. sinuatus has the longest stems, measuring (1.8–) 2.4 (–3.0) m, followed by C. plumbagineus (1.2–) 1.9 (–3.0) m, C. grandiflorus (1.7–) 1.8 (–2.0) m, and C. helenae (1.0–) 1.3 (–2.0) m. In contrast, C. mistus has the shortest stems, ranging from (0.7–) 0.8 (–0.9) m.
The species also exhibit considerable differences in stem surface features. C. grandiflorus is unique in possessing pilose-glandular hairs and a sticky surface texture. C. mistus is characterized by puberulent hairs. In contrast, C. helenae, C. plumbagineus and C. sinuatus have glabrous stems. Notably, all species, except C. grandiflorus, have a non-sticky surface texture.
Leaf morphology (Fig 4 and Table 3).
The leaf characteristics of Commicarpus species exhibit considerable variation in several aspects, including leaf and petiole length, leaf arrangement, lamina shape, lamina dimensions, apex and base shape, and margin structure.
Scale bars 10 mm.
Among the studied species, C. plumbagineus has the largest leaves, with lengths ranging from (27–) 38.5 (–86) mm, whereas C. sinuatus and C. mistus possess the smallest leaves, measuring (6.0–) 10.5 (–13) mm and (7.0–) 13.7 (–27) mm, respectively. Petiole lengths also vary significantly, with C. plumbagineus having the longest petioles (4.0–) 11.6 (–20) mm, while C. sinuatus has the shortest (1.0–) 2.0 (–3.0) mm. Despite differences in size and shape, all species exhibit an opposite leaf arrangement. Two species, C. grandiflorus and C. plumbagineus, exhibit non-fleshy leaves, while the remaining species (C. helenae, C. mistus, and C. sinuatus) possess fleshy leaves, indicating varying degrees of succulence that may correlate with drought tolerance.
Lamina shape displays considerable diversity among species. C. grandiflorus has ovate-triangular leaves, while C. helenae and C. plumbagineus feature broadly ovate forms. C. mistus exhibits ovate to sub-orbicular leaves, whereas C. sinuatus is characterized by sinuate or lobed leaves, a feature that distinguishes it from the other species.
Significant variation is also observed in lamina dimensions. C. plumbagineus has the longest lamina, measuring (23–) 29.5 (–66) mm, and the widest lamina, ranging from (15–) 24.4 (–47) mm. In contrast, C. sinuatus has the shortest lamina at (5.0–) 8.7 (–10) mm and the narrowest lamina at (4.0–) 7.7 (–10) mm.
The lamina apex varies between acute, obtuse, and rounded forms. C. grandiflorus, C. helenae, and C. plumbagineus exhibit acute to obtuse apices, while C. mistus and C. sinuatus are characterized by obtuse or rounded apices.
The lamina base shows notable diversity: C. helenae is distinct with a cordate base, while the other species display truncate to subcordate (C. grandiflorus, C. sinuatus) or truncate to broadly cuneate (C. mistus, C. plumbagineus) bases.
Lamina margin morphology serves as a key diagnostic character among the studied species. C. grandiflorus possesses entire margins, while C. helenae and C. mistus display either entire or sinuately lobed/obscurely sinuated margins. C. plumbagineus exhibits entire to irregularly sinuated margins, and C. sinuatus has distinctly sinuately lobed margins, contributing to its unique identification.
Inflorescence morphology (Figs 5 and 6 and Table 4).
The inflorescence characteristics of Commicarpus species vary significantly in type, surface texture, hair characteristics, and length. C. grandiflorus, C. mistus, and C. sinuatus produce umbels, whereas C. helenae and C. plumbagineus primarily exhibit umbels arranged in groups.
Scale bars 10 mm.
Surface texture also differs among species. The inflorescences of C. grandiflorus are glandular-pilose and sticky, while those of C. mistus are puberulent and non-sticky. In contrast, C. helenae, C. plumbagineus, and C. sinuatus have glabrous and non-sticky inflorescences.
Inflorescence length varies among species. C. helenae has the longest inflorescences, measuring (35–) 51.2 (–70) mm, whereas C. mistus and C. sinuatus possess the shortest inflorescences, measuring (21–) 24.2 (–30) mm and (17–) 22.6 (–30) mm, respectively.
Flower morphology (Fig 7 and Table 5).
The flower characteristics of Commicarpus species exhibit significant variation across multiple traits, including flower and pedicel length, petaloid region and coriaceous segment dimensions, perigonium shape and colour, stamen number and length, ovary shape, ovule count, stigma structure, and the presence of bracts.
Scale bars 10 mm.
Flower size varies considerably among species, with C. helenae possessing the smallest flowers, measuring (4.5–) 5.9 (–10.0) mm, and C. plumbagineus exhibiting the largest, ranging from (12.0–) 17 (–22.0) mm. Pedicel length also varies, with C. sinuatus having the shortest pedicels (1.0–) 1.6 (–2.0) mm, while C. mistus possesses the longest (5.0–) 6.5 (–8.0) mm.
Petaloid region and coriaceous segment lengths (Fig 7 and Table 5).
The length of petaloid region segments differs among species. C. grandiflorus and C. sinuatus exhibit the longest petaloid region segments, measuring (6.0–) 7.5 (–9.0) mm and (6.0–) 7.1 (–9.0) mm respectively. In contrast, C. helenae has the shortest petaloid region segments, measuring (1.5–) 2.0 (–3.0) mm. Coriaceous segment length is greatest in C. plumbagineus (3.0–) 5.2 (–7.0) mm and shortest in C. helenae (2.0–) 2.5 (–4.0) mm.
Perigonium morphology and colour (Fig 7 and Table 5).
Perigonium morphology presents notable interspecific variation. Four species (C. grandiflorus, C. mistus, C. plumbagineus, and C. sinuatus) share a narrowly infundibuliform perigonium shape, though distinctions exist in the tube characteristics. C. grandiflorus features a distinct tube densely covered with external glandular hairs. C. plumbagineus has a distinct tube, while C. mistus displays a puberulent tube. In contrast, C. helenae possesses a widely infundibuliform perigonium with an extremely short tube, setting it apart from the others. Perigonium colour varies among species. C. grandiflorus exhibits pink to reddish-purple perigonia, while C. helenae presents pink flowers. C. mistus has pink to deep magenta perigonia, C. plumbagineus is distinguished by its pure white flowers, and C. sinuatus displays pinkish to purple perigonia.
Stamen characteristics (Fig 7 and Table 5).
The number of stamens differs slightly among species. C. grandiflorus and C. plumbagineus each have three stamens, whereas C. mistus possesses two to three stamens. C. sinuatus has three to four stamens, while C. helenae typically has two stamens.
Stamen length also varies considerably. C. helenae exhibits the shortest stamens, measuring (2.0–) 2.8 (–4.0) mm, whereas C. sinuatus has some of the longest stamens, reaching (15–) 18.1 (–22) mm.
Ovary and stigma structure (Figs 5 and 6 and Table 4).
All Commicarpus species examined in this study produce bisexual flowers with ellipsoid ovaries, each containing a single ovule. The stigma is consistently exerted and capitate across all species.
Fruit morphology (Fig 8 and Table 4).
The fruits of the Commicarpus genus exhibit variations in shape, length, and indumentum across species. C. grandiflorus, C. helenae, C. mistus, and C. sinuatus produce clavate fruits, whereas C. plumbagineus has fusiform-shaped fruits.
Scale bars 1 mm.
Fruit length varies among species. C. grandiflorus produces fruits measuring (5.0–) 6.3 (–7.0) mm, while C. helenae has slightly smaller fruits ranging from (4.0–) 4.8 (–6.0) mm. The longest fruits are found in C. plumbagineus, measuring (7.0–) 8.0 (–9.0) mm, followed by C. mistus at (6.0–) 7.4 (–8.0) mm and C. sinuatus at (5.0–) 6.7 (–8.0) mm.
The indumentum (fruit surface covering) is highly species-specific. C. grandiflorus fruits are covered with numerous sessile glands and finely viscid pubescence, contributing to a sticky texture. C. helenae fruits have long-stalked glands at the apex, with inconspicuous glandular features on the lower parts. C. mistus exhibits puberulent hairs along with prominent long-stalked glands at the apex. In contrast, C. plumbagineus fruits are covered with prominent sessile glands, primarily concentrated at the apex, while C. sinuatus fruits feature sessile glands scattered over the entire surface. Bracts are present in C. helenae but absent in the other species.
Anatomical analysis
Stem anatomy (Fig 9 and Table 6).
The anatomical characteristics of the stem in five Commicarpus species were analyzed based on their transverse sections. The results reveal variations in the structure of the cortex, vascular cylinder, and parenchyma layers across the studied taxa, as summarized below.
Scale bar is 100 μm.
Cortex structure.
The cortex of the examined species consists of collenchyma, chlorenchyma, and endodermis. The number of cortex layers varies significantly between species:
The cortical region shows variation across species in both angular collenchyma and chlorenchyma layers. Angular collenchyma range from 1–2 layers in C. grandiflorus, C. mistus, and C. plumbagineus, while C. helenae and C. sinuatus possess 2–3 layers. The chlorenchyma layer configuration varies more substantially, with C. grandiflorus showing the highest number (5–6 layers), while other species typically display 3–4 layers, except for C. sinuatus which has 2–3 layers. All species share a consistent single compact, barrel-shaped parenchymatous cells endodermis layer.
Vascular cylinder.
Stems are in secondary growth in the outer region. In this way, there are no outer vascular bundles, as these bundles are typical of primary growth. The outer vascular cylinder is continuous, consisting of secondary xylem and phloem in all species. This secondary xylem is composed of numerous libriform fibers interspersed with groups of xylem vessels. The medullary vascular bundles, however, are in primary growth, as they do not form continuous cylinders.
The inner vascular region shows two distinct bundle types:
- Large bundles: Most species contain 2 large bundles, with C. mistus showing slight variation 3 large bundles.
- Small bundles: C. grandiflorus contains 4 small bundles, while all other species possess 6 small bundles.
Parenchyma layers.
The number of parenchyma layers between outer and inner vascular tissues shows considerable variation among species:
- C. helenae exhibits the widest range (4–8 layers).
- C. sinuatus shows moderate variation (4–7 layers)
- C. plumbagineus contains 4–5 layers.
- C. grandiflorus and C. mistus display the narrowest range (3–4 layers).
Leaf anatomy (Fig 10 and Table 7).
The anatomical characteristics of the leaf structure in five Commicarpus species were analyzed using transverse sections, with observations focusing on epidermal thickness, palisade and spongy tissue thickness, and midrib structure. The findings are summarized below.
Scale bar is 100 μm.
Epidermal thickness.
The adaxial and abaxial epidermal thickness varies considerably among the studied species. C. mistus exhibits the thickest adaxial epidermis (11.50–20.57 µm), followed by C. helenae (9.75–19.79 µm) and C. plumbagineus (9.98–17.74 µm). In contrast, C. sinuatus and C. grandiflorus show thinner adaxial epidermal layers, ranging from 8.29–9.57 µm and 8.58–11.29 µm, respectively.
The abaxial epidermal thickness follows a similar trend, with C. mistus presenting the thickest layer (10.29–16.59 µm), followed by C. plumbagineus (8.32–15.12 µm) and C. helenae (5.71–9.65 µm). C. grandiflorus and C. sinuatus again display thinner abaxial layers, ranging from 5.26–7.27 µm and 6.38–8.99 µm, respectively.
Palisade and spongy mesophyll thickness.
Palisade mesophyll thickness shows notable interspecific variation. C. grandiflorus exhibits the thickest palisade layer (84.49–99.47 µm), followed by C. helenae (78.04–88.08 µm). In contrast, C. sinuatus has the thinnest palisade mesophyll (30.57–41.28 µm), indicating reduced photosynthetic tissue compared to other species. Intermediate values are observed in C. plumbagineus (50.33–84.00 µm) and C. mistus (38.92–54.76 µm).
The spongy mesophyll thickness also varies, with C. grandiflorus showing the greatest spongy layer thickness (74.24–84.79 µm). C. sinuatus and C. mistus exhibit moderately thick spongy mesophylls (54.22–72.26 µm and 55.52–71.74 µm, respectively), while C. plumbagineus (56.32–61.49 µm) and C. helenae (44.09–67.70 µm) show slightly thinner layers.
Midrib structure.
The structural configuration of the midrib displays significant variation among the species. The adaxial surface of the midrib in C. grandiflorus and C. plumbagineus is flat, while C. helenae shows a slightly concave adaxial surface, and C. mistus and C. sinuatus exhibit slightly convex adaxial surfaces. The abaxial surface varies from convex in C. grandiflorus and C. helenae to flat in C. mistus, C. plumbagineus, and C. sinuatus.
Petiole anatomy (Fig 11 and Table 8).
The petiole anatomical characteristics of five Commicarpus species were analyzed based on transverse sections, focusing on petiole shape, ground tissue structure, and vascular tissue. The results demonstrate significant interspecific variation as outlined below.
Scale bar is 100 μm.
Petiolar outline and shape.
The petiole outline exhibits notable interspecific variation, particularly in shape and concavity. C. grandiflorus, C. helenae, and C. plumbagineus have cup-shaped petioles, with C. plumbagineus displaying the deepest concavity (very deep concave), while C. grandiflorus and C. helenae are characterized by deep concavity. In contrast, C. mistus and C. sinuatus exhibit arc-shaped petioles, with the adaxial surface being deep concave in C. mistus and slightly concave in C. sinuatus. The abaxial surface across all species remains consistently concave.
Ground tissue structure.
The ground tissue structure, comprising collenchyma and parenchyma layers, varies among species. Collenchyma layers, located beneath the epidermis, range from 1–3 layers in C. grandiflorus to 2–3 layers in C. plumbagineus, and C. sinuatus, while C.mistus from 1–2–2–5 in C. helenae.
Parenchyma layers are distributed over and below the vascular bundles. C. plumbagineus shows the most extensive parenchyma development, with 5–8 layers over the bundles and 6–7 layers below. C. grandiflorus and C. sinuatus have 3–4 and 3–5 layers over the bundles, respectively, with 5–6 layers below. C. helenae presents moderate development with 3–6 layers over and 4–5 layers below the bundles, while C. mistus has the least extensive parenchyma (2–4 layers over and 4–5 layers below).
Vascular tissue organization.
The vascular tissue displays considerable variation in the number, arrangement, and distribution of vascular bundles. The number of main vascular bundles ranges from three in C. grandiflorus, C. mistus, and C. sinuatus to four in C. helenae and five in C. plumbagineus.
The arrangement of the main bundles is species-specific. C. grandiflorus, C. mistus, and C. sinuatus display an open arc formation, while C. helenae and C. plumbagineus show a deep arc configuration.
Small vascular bundles are present in C. helenae, C. plumbagineus, and C. sinuatus but absent in C. grandiflorus and C. mistus. C. helenae has one small bundle, while C. plumbagineus and C. sinuatus possess two each.
Lateral bundles.
The number of lateral vascular bundles also varies. Most species, including C. grandiflorus, C. helenae, C. mistus, and C. sinuatus, have two lateral bundles. In contrast, C. plumbagineus features three lateral bundles, arranged as two primary bundles with an additional smaller bundle (2 + 1), which may further enhance vascular efficiency.
Palynological analysis (Figs 12 and 13 and Table 9)
According to Erdtman [28]; if P/E is 88–100 or 100–114, so pollen grains will be oblate-spheroidal or prolate-spheroidal shapes respectively as Commicarpus species exhibited knowing that 100 refers to apolar pollen grains. Commicarpus pollen grains were classified as large to very large. They were pantoporate, with tubuliferous and spinulose tectum.
Morphometric analysis revealed significant interspecific variation in polar and equatorial axes. C. plumbagineus had the largest polar axis, measuring (106.38–) 117.06 (–127.75) μm, while C. grandiflorus exhibited the largest equatorial axis, ranging from (99.70–) 114.02 (–128.55) μm. In contrast, C. helenae possessed the smallest pollen grains, with polar and equatorial axis measurements of (58.91–) 62.03 (–65.40) μm and (58.56–) 60.41 (–62.37) μm, respectively.
Pollen grain size classification varies among species. C. helenae and C. mistus had large grains. Conversely, C. grandiflorus, C. plumbagineus and C. sinuatus were characterized by very large grains. Shape also served as a distinguishing feature, with C. grandiflorus pollen grains classified as oblate-spheroidal, whereas the remaining four species (C. helenae, C. mistus, C. plumbagineus, and C. sinuatus) displayed a prolate-spheroidal form.
The P/E ratio further supported these findings. C. grandiflorus exhibited a P/E ratio of (92.93–) 94.07 (–98.38) μm, which is below the 100 μm threshold typically used to differentiate between oblate and prolate spheroidal shapes. In contrast, the remaining species had P/E ratios exceeding 100 μm, confirming their prolate-spheroidal classification.
Tubuliferous density and pore size also varies among species. C. grandiflorus, C. mistus, and C. plumbagineus exhibited higher tubuliferous densities compared to C. helenae and C. sinuatus. The largest pore diameter was recorded in C. grandiflorus (4.19–) 4.52 (–4.87) μm, while the smallest was observed in C. mistus (1.91–) 2.23 (–2.27) μm and C. helenae (1.60–) 2.03 (–2.63) μm.
Spinule length also varies among species. C. grandiflorus exhibited the longest spinules, ranging from (1.21–) 2.21 (–3.17) μm, whereas C. sinuatus had the shortest (1.25–) 1.59 (–2.22) μm.
Scoring data and statistical analysis
The collective taxonomic traits were scored to be 54 parameters distinguished as 31 morphological, 15 anatomical and 8 palynological traits (Tables 10 and 11) among Commicarpus species. The operational taxonomic units (OTUs) of all studied species are present at 1.03 where C. grandiflorus is split as delimited genera. At 1.123 OTUs, there are two groups; the first group contains C. helenae and C. plumbagineus while the second group contains C. mistus and C. sinatus at 1.24 OTUs (Fig 14). According to similarity matrix (Table 12), C. grandiflorus and C. helenae are regarded as the distant plant species while C. helenae and C. plumbagineus, C. helenae and C. sinuatus besides C. mistus and C. sinuatus are the close related plant species.
Moreover, P values of Pearson correlation coefficients determined the highest value between morphological and anatomical parameters on the contrary for both morphological and palynological ones. Simple linear regression (SLR) equations represented in the form of scattered plot graphs denoting that morphological vs anatomical parameters expressed as stationary equivalent regression however, other regressed parameters showed the low values (Table 13 and Fig 15).
Species synopsis
Taxonomic treatment
Key of the Commicarpus species in Saudi Arabia based on morphological characteristics.
- Stem and inflorescence are sticky, hairy with glandular hairs ……………….C. grandiflorus
- + Stem and inflorescence are non-sticky, glabrous, puberulent hairs …………………………2
- Leaves are sinuate or lobed; stamen 3 or 4…………………………………...C. sinuatus
- + Leaves are broadly ovate, ovate to sub-orbicular; stamen 2–3………………………………3
- Leaves broadly ovate, ovate to sub-orbicular; bracts are present; the perigonium is widely infundibuliform with an extremely short tube……………………………………... C. helenae
- + Leaves are broadly ovate, ovate to sub-orbicular; bracts are absent; the perigonium is narrowly infundibuliform with a distinct tube.…………………..............................................4
- Leaves broadly ovate; perigonium white; fruit fusiform 7–9 mm………...C. plumbagineus
- + Leaves ovate to sub-orbicular; perigonium pink to deep magenta; fruit clavate 6–8 mm……………………………………………………………………………C. mistus
Key of the Commicarpus species in Saudi Arabia based on anatomical characteristics.
- Petiole cup-shaped, with adaxial very deep concave, main vascular bundles 5 in deep arc shaped ………………………………………………………………………………….C.plumbagineus
- + Petiole cup- or arc-shaped, with adaxial deep or slightly concave, main vascular bundles 3 or 4 in deep or open arc shaped ………………………………………………………………..2
- Petiole cup- or arc-shaped, with adaxial deep concave, main vascular bundles 4 in deep arc shaped…………………………………………………………………………. C.helenae
- + Petiole cup- or arc-shaped, with adaxial deep or slightly concave, main vascular bundles 3 in deep or open arc shaped………..............................................................................................3
- Petiole cup- or arc-shaped, with adaxial slightly concave, main vascular bundles 3 in deep or open arc shaped with two small vascular bundles ………………………………C.sinuatus
- + Petiole cup- or arc-shaped, with adaxial deep concave, main vascular bundles 3 in open arc shaped without small vascular bundles …………………………...…………………………...4
- Petiole cup-shaped, with adaxial deep concave, main vascular bundles 3 in open arc shaped without small vascular bundles …………………………………………………C.grandiflorus
- Petiole arc-shaped, with adaxial deep concave, main vascular bundles 3 in open arc shaped without small vascular bundles ………………………………………………………C. mistus
Discussion
Morphological traits have historically served as primary taxonomic tools and continue to play a crucial role in contemporary plant systematics. They reveal both external and internal characteristics and are instrumental in interpreting species-level relationships. Morphological variation among Commicarpus species likely reflects adaptive responses to arid environments while maintaining taxonomic significance [25].
The present study provides a comprehensive morphological evaluation of five Commicarpus species occurring in Saudi Arabia: C. grandiflorus, C. helenae, C. mistus, C. plumbagineus, and C. sinuatus. The results are compared with the descriptions provided in the foundational works of [11,13], which included all five species, and with [15], whose taxonomic revision was limited to C. helenae and C. plumbagineus. Overall, the current findings are largely consistent with earlier taxonomic treatments, while offering more precise morphometric data that enhance species delimitation and deepen our understanding of morphological variability.
Commicarpus grandiflorus was clearly distinguished by its sticky stems densely covered with pilose-glandular hairs—a defining feature consistently reported by [11,13]. This trait remains taxonomically reliable, as it was not observed in any of the other studied species. The current study also quantified stem length and growth orientation, identifying accumbent to ascending growth forms that had not been previously described in detail.
Leaf morphology exhibited marked interspecific variation, particularly in margin type and texture. C. grandiflorus retained its ovate-triangular, entire leaves, as documented in earlier accounts, while C. helenae and C. sinuatus were confirmed to have sinuate or lobed margins, corroborating the observations of [13]. Quantitative data from the present study—such as petiole length, lamina dimensions, and texture (fleshy vs. non-fleshy)—provided a more rigorous framework for distinguishing among species. The variation in apex morphology among studied species may have ecological implications, influencing water runoff and photosynthetic efficiency [34].
The floral morphology of the examined Commicarpus species revealed distinctive features that both confirm and refine previous descriptions [11,13,15]. C. grandiflorus and C. plumbagineus both exhibited narrowly infundibuliform perigonia with well-developed basal tubes and three free stamens, differing in flower color—pink to reddish-purple in C. grandiflorus and white in C. plumbagineus [11,13]. C. helenae was characterized by a widely infundibuliform perigonium with a short tube, pink coloration, and two stamens, along with sessile and stalked glands on the fruit apex [11,13,15]. C. mistus displayed narrowly infundibuliform, deep pink to magenta flowers with a puberulent tube and a variable number of stamens (2–3), while C. sinuatus featured pinkish to purple flowers with a prominent floral tube and 3–4 stamens [11,13]. These detailed floral features serve as robust taxonomic indicators for species delimitation within the genus.
Inflorescence and fruit morphology also played a significant role in distinguishing among the species. Inflorescence types were umbellate in C. grandiflorus, C. mistus, and C. sinuatus, and whorled in C. helenae and C. plumbagineus. Fruit shapes ranged from clavate (C. grandiflorus, C. mistus, C. helenae, C. sinuatus) to fusiform (C. plumbagineus), in agreement with earlier descriptions and further validated by this study’s observations on gland distribution. Notably, the fruits of C. grandiflorus were found to be viscid and densely covered with sessile glands—a feature that aligns closely with the “prominently gland-warted” fruit surfaces described by [11,13].
Although most morphological traits remained stable across geographical distributions, the present study recorded slight variations in some measurements (e.g., leaf and fruit length, perianth size), which may reflect environmental influences or regional morphological plasticity. Observed differences between geographically distinct populations may indicate ecological adaptation and/or underlying genetic divergence. Notably, when comparing C. helenae and C. plumbagineus populations from Saudi Arabia with their counterparts in southern Africa, as documented by [15], the Saudi specimens exhibited shorter petioles and variations in leaf and floral dimensions, suggesting potential ecological adaptation. These observed differences merit further investigation through molecular analyses to evaluate their phylogenetic implications.
Anatomical characterization serves as a complementary tool to morphological analysis in differentiating species within the same genus. It allows taxonomists to assess how external species appearance correlates with specific habitat types [35]. Anatomical characters, particularly stem and leaf structures, represent reliable systematic markers and are often congruent with molecular phylogenies [36]. The anatomical structures of stems and leaves in Commicarpus_species (Nyctaginaceae) align with previous descriptions by [17,18,37]. This study highlights interspecific variations across several anatomical parameters, underscoring adaptations to different environmental conditions and reinforcing their taxonomic significance.
Transverse sections of leaves reveal substantial interspecific differences in epidermal thickness, mesophyll structure, and midrib configuration traits critical for understanding physiological adaptation. The mesophyll in Commicarpus species consists of palisade and spongy parenchyma. Palisade cells increase the internal leaf surface, thereby enhancing photosynthesis rates [38], while spongy mesophyll facilitates carbon dioxide circulation throughout the leaf to maintain high photosynthesis rates. Variation in mesophyll organization and vascular bundle architecture suggests functional adaptations related to photosynthetic efficiency and mechanical support. The spongy mesophyll thickness also varies, with C. grandiflorus showing the greatest spongy layer thickness (74.24–84.79 µm), suggesting a well-developed internal air space system conducive to efficient gas exchange [39].
Commicarpus mistus exhibits the thickest epidermis (adaxial: 11.50–20.57 µm; abaxial: 10.29–16.59 µm). The increased epidermal thickness in C. mistus may contribute to enhanced structural support and water retention, reflecting adaptations to drier environments [40]. C. grandiflorus presents the thickest palisade (84.49–99.47 µm) and spongy mesophyll layers (74.24–84.79 µm), indicating a high capacity for photosynthesis and gas exchange, consistent with adaptations to arid environments. Conversely, C. sinuatus has the thinnest palisade mesophyll (30.57–41.28 µm), potentially reflecting reduced photosynthetic efficiency or adaptation to shaded habitats.
Midrib morphology also varies: very deep concave adaxial surfaces in C. plumbagineus likely confer structural rigidity, whereas the semi concave surface observed in C. sinuatus may enhance leaf flexibility. These variations in midrib morphology may relate to differences in leaf rigidity and structural support, potentially reflecting species-specific adaptations to varying environmental conditions [41].
The structure of the petiole offers significant taxonomic diagnostic value, as it appears relatively unaffected by environmental variations [37]. Among the studied organs, petiole anatomy provided some of the most taxonomically informative features, particularly in terms of shape, tissue organization, and vascular configuration.
Petiole outlines ranged from cup-shaped in C. grandiflorus, C. helenae, and C. plumbagineus to arc-shaped in C. mistus and C. sinuatus. Ground tissue analysis revealed that C. plumbagineus had the most extensive parenchyma development, with up to eight layers above and seven layers below the vascular bundles, suggesting both enhanced mechanical support and storage capacity. In contrast, C. mistus had the least developed parenchyma.
The current study reveals notable differences among Commicarpus species. C. grandiflorus exhibits more rows of chlorenchyma compared to other species. In contrast, C. helenae and C. sinuatus display a greater number of collenchyma layers (2–3). Collenchyma provides mechanical support to growing parts through thickened walls, which also aids in protection against sunlight and water loss [17,18]. However, the presence of a collenchymatous hypodermis is not considered a xeromorphic adaptation here, as it serves as basic structural support commonly found in many young mesophytic stems.
An examination of the vascular cylinder shows that C. mistus possesses three large inner bundles, whereas other species have two. C. grandiflorus has four small inner bundles, compared to six in the remaining species. The development of parenchyma between vascular tissues varies among taxa, with C. helenae exhibiting the greatest number of layers (4–8), suggesting enhanced storage or internal buffering capacity. In contrast, C. grandiflorus and C. mistus have fewer layers (3–4), indicating reduced internal differentiation.
Vascular bundle arrangement was species-specific. C. plumbagineus exhibited the most complex configuration. This intricate architecture suggests increased hydraulic efficiency and mechanical reinforcement. Small vascular bundles were observed in C. helenae, C. plumbagineus, and C. sinuatus, but were absent in C. grandiflorus and C. mistus. Their presence may enhance vascular supply and structural flexibility traits associated with evolutionary divergence within Nyctaginaceae. The arrangement of the main bundles among studied species suggests that the differences in vascular support are potential adapted with mechanical stress. Moreover, The presence of the additional bundles (small ones) may contribute to enhanced vascular supply and mechanical stability [42].
A recent study by Pakravan et al. (2023) [19] on the systematics of Nyctaginaceae in Iran, which included C. helenae, reveals further differences in these anatomical characteristics. The number of collenchyma layers in the stem and petiole of C. helenae observed in the present study is greater than that reported by Pakravan et al. (2023) [19].
The best taxonomic purposes are achieved by combining evidence from different biological fields or levels to illustrate the inter- and intra-relations among different species. The analysis of pollen grain description offers the genetical stable markers for enhancing taxonomic identification [43]. Pollen morphology constitutes a genetically stable and evolutionarily informative dataset, reinforcing its value in taxonomic and phylogenetic inference [44]. The pollen morphology observed in the studied Commicarpus species, ranging from prolate spheroidal to oblate spheroidal forms, aligns with characteristics previously reported for other members of the Nyctaginaceae family [6,45].
Although molecular tools have revolutionized plant taxonomy by providing objective, DNA-based evidence to classify plants, resolve complex relationships, and identify cryptic species that are morphologically identical, palynology offers robust morphological markers that assist in the delimitation of closely related species, genera, and families. It is often less affected by ecological conditions compared to genome mutation, offering high genetic stability. Accordingly, palynology plays an incontrovertible role not only in “basic research” concerning botanical taxonomy, phylogeny, phenology and reproductive biology, but also in several fields of applied research that focus on measuring environmental variables focusing on sustainability and climatic changes [46,47].
Struwig et al. (2013) [20] examined the pollen morphology of Southern African Boerhavia and Commicarpus (Nyctaginaceae). Two Commicarpus species in the study which are C. helenae and C. plumbagineus, both of them occur in Saudi Arabia. The sculpture patterns of these species in the present study are consistent with their findings; however, differences are observed in the length of spinules and pore diameter. Specifically, the spinule length in C. helenae is larger than the measurements reported by Struwig et al. (2013) [20]. Conversely, the spinule length in C. plumbagineus is smaller than that recorded by Struwig et al. (2013) [20]. Similarly, the pore diameters in C. helenae and C. plumbagineus are smaller than the values reported by Struwig et al. (2013) [20], respectively.
A more recent study by Pakravan et al. (2023) [19] on the systematics of Nyctaginaceae in Iran, which also included C. helenae, reveals further differences in these palynological characteristics. The spinule length of C. helenae in this study is smaller than the range reported by Pakravan et al. (2023) [19]. Likewise, the pore diameter of C. helenae is also smaller than the range recorded by Pakravan et al. (2023) [19].
Morphologically, C. grandiflorus exhibits an oblate spheroidal pollen form with a P/E ratio of [(92.93–) 94.07 (–98.38) μm], which remains below the 100 μm threshold typically used to differentiate between oblate and prolate spheroidal shapes. In contrast, the remaining species in this study have P/E ratios exceeding 100 μm, confirming their classification as prolate spheroidal.
The consistent presence of a tubuliferous and spinulose tectum across all studied species suggests a shared evolutionary trait within the genus. However, the observed variations in polar and equatorial axis dimensions, P/E ratios, spinule length, pore diameter, overall pollen shape, and size provide valuable taxonomic characters for differentiating among these species.
From the scored data and statistical analysis, C. helenae and C. sinuatus are the transient plant species among studied species, on the other hand, C. grandiflorus is the most distant species among them. The morphological and anatomical parameters are the most compatible and homogenetic traits that reflect on each other more than palynological traits. The expression outwards and inwards for plant nature is very susceptible to each other. Hence, adaptable changes within plant species affect the morphological and anatomical nature more than palynological characters. From similarity index, we can observe much more similarity value among C. helenae, C. plumbagineus, C. mistus and C. sinuatus with less dissimilarity value between C. grandiflorus and C. helenae only to confirm that all studied species related to each other and not suggest excluding any one as a delimited genera. The congruence among morphological, anatomical, and palynological datasets supports an integrative taxonomic framework for resolving species boundaries within Commicarpus. Combing among different plant taxonomic tools including morphology, anatomy and palynology indicate that there is a mutual homogenous compatibility between traditional and modern taxonomic tools to obtain comprehensive optimum clear picture of the taxonomic status for studied species.
The taxonomic keys presented for Commicarpus species in Saudi Arabia provide a precise diagnostic framework by combining external morphological traits with internal anatomical features.
The morphological key effectively separates the five species based on observable characters. C. grandiflorus is distinct for its sticky, glandular-hairy stems, while C. sinuatus is recognized by its sinuate leaves and higher stamen number. The remaining species are differentiated using floral and fruit characteristics, including perigonium shape and color, bract presence, and fruit type (fusiform in C. plumbagineus vs. clavate in C. mistus). These characters are taxonomically stable and practical for field identification.
The anatomical key adds further resolution, focusing on petiole morphology and vascular bundle configuration. C. plumbagineus is unique in having five vascular bundles in a deep arc, while other species show variations in bundle number (three or four), arc shape, and presence or absence of interspersed traces. These internal features are less environmentally influenced, making them valuable for confirming species identity, especially in morphologically similar taxa.
The existence of climate change is confirmed by various evidences from different sources that can be used to reconstruct past climates. Plant species have responded to climate change by range shifting and increasing species richness. Plant taxonomy could be an important way for species distribution to counterbalance rapid climate change. morphological, anatomical and palynological traits are likely to influence the ability of species to take advantage of potentially favorable conditions arising from climate change. Plant species can also adjust to new conditions through phenotypic plasticity [48]. Generally plants respond to climate change impacts in different ways. The dispersal of plant species to new and more favorable sites is the most important plant range shifting in response to climate change impacts. In light of the foregoing, the new Commicarpus species are discovered recently at countries close to the same latitude of Jazan region; C. altus Thulin from central Somalia and C. ogadenensis Thulin from southeastern Ethiopia [49].
Conclusion
This comprehensive study of Commicarpus species in Saudi Arabia has yielded valuable insights into their morphological, anatomical, and palynological diversity. The observed interspecific variations in growth habit, stem and leaf structure, inflorescence and fruit morphology, as well as detailed anatomical and palynological characteristics, have proven to be robust taxonomic markers. The development of identification keys based on both morphological and anatomical features of the petioles enhances the accuracy of species delimitation within the genus in Saudi Arabia. These findings not only facilitate the identification and classification of Commicarpus species in the region but also contribute to a deeper understanding of their evolutionary relationships and ecological adaptations. Taxonomy of Commicarpus species can estimate the impact of climatic changes on a specific area by classifying, mapping, and monitoring to detect shifts in their distribution, phenology, and community structure. By utilizing historical records and modern biodiversity surveys, taxonomists can measure how species compositions change over time and predict future responses to climate stressors.
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