Comparative palynology and taxonomic implication of Jasminum L. (Oleaceae) species from Pakistan on the bases of scanning electron microscopy

Abstract

Jasminum L. is the largest genus containing ~200 species found wild mostly in the tropical regions of the world. The comparative palynological study of nine Pakistani Jasminum species with SEM showed zonocolpus, trilobate, and tricolpus pollen types with simple endocolpus apertures which are plesiomorphic and conserved in the Jasminum species. The equatorial pollen view was prolate, subprolate, and perprolate with elliptic, lobate, subcircular whereas polar view was subtriangular in all species. Few characters were specific to some species like heteropolarity in Jasminum grandiflorum and foveolate exine ornamentation with rounded heterobrochate in Jasminum angulare whereas reticulate and angular homobrochate character was common in other species. The UPGMA dendrogram based on qualitative characters did not support the phylogenetic classification of the genus Jasminum as these are highly conserved. The quantitative data showed more variation in some characters whereas few characters showed little or no variation. A greater variation in pollen size was observed among the variants of same species, for example, Jasminum humile showed highly variable polar length and equatorial diameter as compared to other species. Minimum variation was observed in colpus length which divided all species in to two groups. The large lumina were specific to Jasminum nitidum and broader muri was the prominent characteristic of Jasminum angulare. Some species like Jasminum sambac and Jasminum azoricum were unable to develop true pollen due to structural or functional disabilities. So, the quantitative characters of pollen are only suitable for palynological based grouping of Jasminum species but less suitable to infer their evolutionary relationship.