Pollen morphology and character evolution in Jatropha L. (Euphorbiaceae) from India: an integrative phylogenetic approach

Pollen morphology of 15 Indian taxa of Jatropha was investigated using light microscopy and scanning electron microscopy to evaluate the taxonomic significance of pollen characters and to reconstruct the evolution of pollen exine traits within the genus. All species possessed large, inaperturate pollen grains with a characteristic croton pattern and a spherical to spheroidal shape. Clavae were arranged in pentagonal to heptagonal rosettes, and pollen diameter ranged small-size in J. maheshwarii to large-size in J. curcas. The croton pattern varied from lax to moderately dense and highly dense, with clavae forming the principal ornamentation units. Several qualitative exine characters showed marked variation, including polar outline of clava (rounded or triangular), clava apex (rounded, slightly pointed, or pointed), clava distribution (uniform or polymorphic), and striation pattern (longitudinal or variously transverse), with striae varying from deep to shallow. Intraluminal elements exhibited either a sparse or dense distribution and were arranged as aggregates or in a randomly dispersed pattern. The results indicate that qualitative characters are more taxonomically informative for species delimitation than quantitative traits such as pollen size and exine thickness. Ancestral state reconstruction using maximum likelihood, as implemented in MESQUITE, revealed contrasting evolutionary patterns among exine characters. The exclusive occurrence of gemmae in J. nana represents an autapomorphic character that supports its evolutionary distinctiveness. Overall, the findings provide new insights into the evolution of pollen exine architecture and establish a robust morphological framework for species delimitation and phylogenetic interpretation within Jatropha.