Micromorphological leaf epidermal traits as potential taxonomic markers for infrageneric classification of Oxytropis (Fabaceae)

A new species of Astragalus (Fabaceae) from the Irano-Turanian biodiversity hotspot: an integrative approach

BACKGROUND

The genus Astragalus is the largest and one of the most diverse genera of flowering plants, particularly in the Northern Hemisphere, with a significant concentration of species in the Irano-Turanian region. Within this genus, section Hymenostegis is notable for its complexity and high levels of endemism, especially in northwestern Iran. During recent field explorations in West Azarbaijan province, a distinct population of Astragalus was identified, differing from known species within section Hymenostegis. This study aimes to describe and analyze this new species and clarify its relationship with closely related taxa using an integrative approach.

RESULTS

Astragalus kuzehrashensis sp. nov. is described following detailed morphological comparisons with its closest relatives, A. chehreganii and A. hakkianus. The new species is distinguished by unique stipule characteristics, leaflet shape, inflorescence structure, and seed micromorphology. Molecular phylogenetic analysis using ITS and ycf1 sequences reveals that A. kuzehrashensis forms a clade with A. chehreganii and A. hakkianus, although it exhibits genetic differences. Genome size estimation confirms that A. kuzehrashensis is hexaploid (2n = 6x = 48), aligning it more closely with A. hakkianus than with the tetraploid A. chehreganii. The distinct morphological characters and genomic data support recognizing A. kuzehrashensis as a new species within section Hymenostegis.

CONCLUSIONS

The identification of A. kuzehrashensis underscores the importance of an integrative taxonomic approach, combining morphological, molecular, and cytogenetic data to resolve species boundaries within complex groups like Astragalus section Hymenostegis. This study highlights the rich biodiversity of the Irano-Turanian floristic region, emphasizing the need for ongoing exploration and conservation efforts, particularly in areas of high endemism. Our findings contribute to a deeper understanding of the taxonomy and evolutionary relationships within the genus Astragalus.

Chemotaxonomy compared to morphological and anatomical taxonomy of five Hibiscus species

Hibiscus is a charismatic genus of the Malvaceae family that is noted for its diversity, lacking identifiable characteristics for distinguishing its various species. Therefore, there is an urgent need to develop authentication methods for genus delimitation and species delineation. The present study aims to discern the taxonomic relationships between the well-known, globally familiar, and economically important five Hibiscus species, namely: H. × rosa-sinensis, H. sabdariffa, H. schizopetalus, H. syriacus and H. tiliaceus based on traditional morphological and anatomical characteristics compared to the contemporary chemotaxonomy. In this context, the leaf-based methanolic extracts of the studied species were analyzed by Gas Chromatography-Mass Spectrometer (GC-MS) to estimate their secondary metabolites similarity. In addition, selected qualitative morphological and anatomical traits including leaf venation patterns, epidermal micromorphology, stomata types and trichomes diversity, petiole serial sectioning (outline, adaxial groove features, vasculature traces arrangement), and midrib characteristics of the studied species were investigated. The results of both chemotaxonomy and traditional taxonomy exhibited a remarkable agreement in the delineation of the five studied species. Specifically, the chemotaxonomy-based dendrogram separates the studied species into two main clusters with the H. sabdariffa as an outlier species in a single cluster and the remaining four species as another cluster with variant distances in its similarity indices. Similarly, the traditional morphological and anatomical characteristics revealed distinct traits for H. sabdariffa compared to the remaining four species. The findings of this study highlight the significance of integrating the structural features with phytochemicals profiling as a potential approach that could be harnessed for the delineation of the taxonomically challenging Hibiscus genus.

Taxonomic relevance of leaf surface micromorphology in Korean Clematis L. (Ranunculaceae)

Clematis, one of the largest genera of the family Ranunculaceae, has a wide array of morphological variation and is considered the most difficult group of taxa in terms of infrageneric discrimination. This study assessed the leaf micromorphological features of 19 Clematis taxa (16 species and three varieties) found in Korea. The leaf surface features were studied under scanning electron microscopy, and the stomatal counting and measurement were carried out under light microscopy. Clematis are hypostomatic, meaning the stomata are only found on the abaxial surface of the leaf. Observed taxa showed near uniformity in the epidermal cell type, structure, and morphology on both surfaces of the leaf. Differences were observed in the presence and absence and/or abundance of trichomes on both the adaxial and abaxial surfaces, the epidermal cell boundary, and the periclinal and anticlinal wall of the cells. Differences were also observed in the number of the epidermal cells connected with the stomata on the abaxial surface, with small differences noted in epidermal cell shapes. The ANOVA showed a significant variation in the stomata density in the studied taxa (P < 0.0001). The cluster analysis based on 13 leaf micromorphological features generated four major clusters. These results indicated similarities in certain key leaf micromorphological features among taxa from the Tubulosae, Clematis, and Virona sections. In the genus Clematis, as with other morphological characteristics, using leaf micromorphological characters alone, which possess limited taxonomic value, proves inadequate for resolving infrageneric relationships. However, incorporating certain features with other morphological characteristics offers a possible alternative means of determining the infrageneric relationships within the genus.

Taxonomic implications of normal and abnormal stomatal complexes in Indigofera L. (Indigofereae, Faboideae, Fabaceae)

This study is the first to report the foliar and stem epidermal micro-morphology of 13 taxa of Indigofera L. (Fabaceae) using light (LM) and scanning electron microscopy (SEM). The micro-morphological characteristics studied here are related to the epidermal cell shape, size, frequency, anticlinal wall pattern, and stomatal complex types, size, position, frequency, and index. The study revealed 19 major normal stomatal types with eight subtypes and seven major abnormal stomatal types with 13 subtypes. The stomatal index was lower on the abaxial leaf surface than on the adaxial surface. Notably, the adaxial surface of I. hochstetteri had the highest stomatal index (27.46%), while the abaxial surface of I. oblongifolia had the lowest (9.95%). The adaxial surface of I. hochstetteri also displayed the highest average stomatal frequency (38.67), while the adaxial surface of I. spinosa had the lowest average frequency (9.37). SEM analysis revealed that most leaves had slightly sunken to sunken stomata, while stem stomata were positioned at the same level as epidermal cells in most taxa. Indigofera's foliar and stem epidermal anatomy recommends their application as baseline data coupled with other taxonomic data for the delimitation and differentiation of closely related taxa in the genus. The study provides a comprehensive description, illustrations, images, and micrographs of the stomatal types, as well as a taxonomic key for distinguishing the studied taxa of Indigofera.

Genetic Diversity of Oxytropis Species from the Center of the Genus Origin: Insight from Molecular Studies

The genus Oxytropis (Fabaceae) was formed from the ancient species of Astragalus presumably approximately 5.6 Ma ago in Southern Siberia. Our study summarized data on the genetic diversity of 69 populations of 31 Oxytropis species in the center of origin of the genus based on the sequencing of plastid genome markers. Most of the populations (82.6%) are characterized by high gene diversity (0.600–1.000), which indicates a relatively stable state. Phylogenetic relationships between most Oxytropis species remain unresolved. Three genetic complexes and four phyletic lineages have been identified. Some species form weakly differentiated complexes, which is probably caused by their relatively recent divergence and the demography processes, as well as interspecific hybridization and polyploidy characteristic of Oxytropis species.