Floral micromorphology and microsporogenesis of the gynodioecious herb Glechoma longituba (Lamiaceae)

Abstract

Gynodioecy, the phenomenon of having both hermaphrodite and female (i.e. male‐sterile) individuals within the same population, is an important intermediate step in the evolution of separate sexes in flowering plants. In this study, we investigated the floral micromorphology and microsporogenesis of the gynodioecious herb Glechoma longituba from four natural populations in Korea. The floral micromorphological characters of the different sex morphs were examined and compared using scanning electron microscopy (SEM), and the ultrastructure of microspores during microsporogenesis was studied. We also examined the development of anthers and pollen grains in the three sexual morphs (i.e. hermaphrodites, females, and gynomonoecious, i.e. individuals with a mixture of female and hermaphroditic flowers) by embryological investigation. The major difference in anther development between the three phenotypes was the early disintegration of the tapetal cells in the anthers of female flowers. While mature fertile pollen grains were found in both hermaphrodite and gynomonoecious phenotypes, females did not produce any pollen grains. In addition, both fertile and sterile pollen grains in gynomonoecious phenotypes were frequently observed. The results of the present study indicate that floral micromorphological characters were not distinct between sexual morphs of G. longituba, except for the structure of the inner cell surfaces of the anther. The observed tapetum abnormalities and degeneration of pollen grains in both gynomonoecious phenotypes and females may be the consequence of inbreeding depression in hermaphrodites.

rDNA Loci Evolution in the Genus Glechoma (Lamiaceae)

“…Glechoma hederacea and G . longituba have a gynodioecious sexual system comprising females and hermaphrodites [37–38]. Only hermaphrodites were examined.…”

Comparative Floral and Pollen Micromorphology of Leonurus japonicus and L. macranthus (Lamiaceae)

“…L. [25], and Glechoma longituba (Nakai) Kuprian. [26]. Recently, studies on the micromorphology of Lamiaceae focused mainly on the structure and distribution of leaf trichomes [27][28][29][30][31][32][33][34] and on the taxonomic implications of pollen morphology [27,32,[35][36][37][38][39].…”

“…The floral epidermis has been observed using scanning electron microscopy in the following genera or species: Lycopus L. [23], Lycopus maackianus Makino [24], Glechoma L. [25], and Glechoma longituba (Nakai) Kuprian. [26]. Recently, studies on the micromorphology of Diversity 2021, 13, 533 2 of 15 Lamiaceae focused mainly on the structure and distribution of leaf trichomes [27][28][29][30][31][32][33][34] and on the taxonomic implications of pollen morphology [27,32,[35][36][37][38][39].…”