Floral biology, pollination mechanism and embryo development in Zeylanidium maheshwarii (Podostemaceae)

Abstract

Zeylanidium maheshwarii is one of the 23 endemic species of Indian Podostemaceae, the largest family of fresh water aquatic plants in the world. The family is unique in many ways, be it their habitat, plant body or the reproductive attributes. We looked into some of the reproductive attributes of the species encompassing floral biology, mechanism of pollination and embryo development. The flower is highly reduced, and the species can be easily identified from the rest of the Zeylanidium clade by two features—the presence of a gynophore and the multi-lobed stigma. The pollen grains are released in units of two—the acalymmate dyads. The exine ornamentation is microechinate with discernible apertural and interapertural regions. Pollination is accomplished by autonomous self-pollination, which occurs above the water level. The formation of three-celled embryo sac in the species is the result of precocious degeneration of the central cell prior to syngamy. Absence of central cell before fertilization leads to absence of double fertilization and endosperm in the species, and this features reiterates the general cause of usual absence of double fertilization among the podostemads.