Morpho-palynological and ultrastructural characterization of Solena Lour. (Cucurbitaceae)

The genus Solena Lour. (Cucurbitaceae), has remained morpho-palynologically underexplored despite its taxonomic placement within the tribe Benincaseae. Here, we provide the first integrative palynological assessment of two representative species, S. amplexicaulis and S. heterophylla, using light microscopy and scanning electron microscopy. Both species exhibit a conserved androecial architecture of three sigmoid stamens with bithecal, bisporangiate anthers characterized by pronounced intersporangial ridges, and multicellular as well as glandular trichomes. Pollen grains of Solena heterophylla and S. amplexicaulis are medium to large, tricolporate, prolate, isopolar, and radially symmetrical, with a tectate exine and exhibiting a distinctive verrucate ornamentation. Notably, this verrucate exine pattern is unprecedented within the Benincaseae, where microreticulate ornamentation predominates, thereby providing a robust diagnostic character to resolve the historically unstable boundaries from morphologically allied genera such as Bryonia L., Kedrostis Medik., Melothria L., and Zehnaria Endl. within the tribe. These findings refine the systematic circumscription of Solena and establish critical micromorphological benchmarks for future taxonomic delimination, reproductive, and breeding investigations within the Cucurbitaceae.