Exploration of Pollen Traits and Their Taxonomic Relevance in Selected Taxa of the Subfamily Papilionoideae from Hainan Island, China

Abstract

ABSTRACT The Papilionoideae is one taxonomically complex subfamily with high economic and medicinal potential. The pollen micro-morphology and taxonomic relevance of this subfamily are still poorly known in the island. Therefore, this study aims to provide new palynological information to correctly identify and define species boundaries within the subfamily. The species were collected from different geographical regions of Hainan Island. Both light and scanning electron microscopic techniques were used to observe pollen traits. Additionally, principal component analysis was performed to elucidate the variation among the taxa. A significant variation was found in exine sculpturing i.e. most of the taxa have reticulate type pollen while Desmodium triflorum has a psilate exine pattern. Variations were found on the surface of the reticula that can help to delimit the species from one another. Pollen type was observed as tricolporate and rarely tricolpate. Similarly, the colpus surface membrane morphology may also vary significantly from species to species i.e. scabrate, verrucate, gemmate, rugulate patterns. Besides, the mergo having various sculpturing found in Canavalia rosea, Desmodium triflorum, D. microphyllum Glycine max, Macroptilium atropurpureum, Erythrina crista-galli and Zornia gibbosa should be considered as a potential taxonomic trait for the subfamily. The maximum P/E ratio was found in Zornia gibbosa (2.24). Similarly, the maximum pollen size was found in Alysicarpus vaginalis (34.64 × 33.99 µm). Our study explored the pollen morphological traits and can be helpful to correctly identify the species and define species boundaries within Papilionoideae at various taxonomic levels. This study strengthens and supports the taxonomic position of the subfamily and will provide bases for further phylogenetic and molecular studies of Papilionoideae. HIGHLIGHTS Various taxa of the subfamily Papilionoideae were collected from different geographical regions of Hainan Island, South China. Both light and scanning electron microscopic techniques were used to analyze the ultra-sculpturing of the pollen. Most of the taxa have reticulate exine patterns but variations were found in supra-tectal elements and colpus surface membrane morphology. These variations in pollen traits have significant taxonomic potential and will strengthen the taxonomy of Papilionoideae. This study can help to correctly identify and define species boundaries at various taxonomic levels of the Papilionoideae and will solve the taxonomic problem.