Taxonomic and ecological significance of seed morphology and ultrastructure in species of Lotus formerly classified in Dorycnium (Leguminosae – Loteae)

Abstract

Seed morphology and ultrastructure of Lotus species from sections Dorycnium (L. dorycnium and L. graecus), Bonjeanea (L. rectus, L. hirsutusand L. strictus) and Lotus (L. corniculatus) have been studied using light and scanning electron microscopy. The seeds of studied species have a conservative structure typical for most Papilionoideae. Seed size, shape and color only partially allow distinguishing species in the studied group. The most morphologically distinguishable seeds are those of members of the polyphyletic section Bonjeanea, with L. rectus having the smallest and L. strictus the largest seeds. Seed size ranges in the species of the section Dorycnium overlap both between the members of the section and with seeds of L. hirsutus (section Bonjeanea). Seed surface ultrastructure around the hilum is very stable among studied species, whereas that on the lateral seed side is more variable. The types of surface sculpture on the lateral seed side do not strongly correlate with taxonomic position of species, but some correlations with eco-geographical patterns can be traced. The type of seed surface micromorphology with inconspicuous primary sculpture and thick secondary cuticular deposits was revealed in taxa, which distribution is connected with the Mediterranean region (L. hirsutus, L. dorycnium subsp. gracilis and partially L. rectus). Foveolate-papillose primary sculpture with thin secondary cuticular deposits is typical for species occurring in milder climate (L. corniculatus, L. strictus, L. graecus). Studied species can be subdivided into two groups by endosperm thickness. We believe that thin endosperm revealed in L. strictus and L. corniculatus may be a trait connected with the acceleration of development when spreading from the Mediterranean to the temperate climatic zone.