Development of the floral shoot and pre-anthesis cleistogamy inHydrobryopsis sessilis(Podostemaceae)

Abstract

The reproductive biology of Hydrobryopsis sessilis (Podostemaceae, subfamily Podostemoideae), a reduced, threatened, aquatic angiosperm endemic to the Western Ghats of India, was examined. This is the first report on the transition from the vegetative to the reproductive phase in this plant, describing floral ontogeny, pollination and the breeding system. The cytohistological zonation of the apical meristem of the reproductive thallus is identical to that of the apical meristem of the vegetative thallus. The floral shoots do not replace vegetative shoots (i.e. the vegetative shoots never bear flowers), but form at new sites at the tip of the flattened plant body. Each floral shoot meristem is tiny, deep-seated and concave and arises endogenously following lysigeny. The floral shoot meristem gives rise to four to six bracts in a distichous manner. The development of spathe, stamens and carpels is described. The ab initio dorsiventrality of the carpels and the occurrence of endothelium in the ovules are reported. The mature stigmas and anthers lie close to each other. The pollen germinates within undehisced anthers and the pollen tubes enter the stigmas in the unopened floral bud, leading to pre-anthesis, complete, constitutional cleistogamy under water. The seed set is 63.2%. A significant finding is the penetration of several pollen tubes into the filaments of stamens in 16% of the flower buds, indicating a trend towards cryptic self-fertilization. The Indian Podostemoideae appear to show a shift from xenogamy or geitonogamy or autogamy in a chasmogamous flower to complete autogamy in a cleistogamous flower. The floral modifications leading to cleistogamy in H. sessilis have been identified.

Evolution of unusual morphologies in Lentibulariaceae (bladderworts and allies) and Podostemaceae (river-weeds): a pictorial report at the interface of developmental biology and morphological diversification

“…, 2011 ). More derived American and all non-American members of Podostemaceae are wind-pollinated or cleistogamous ( Philbrick and Les, 1996 ; Cook and Rutishauser, 2007 ; Sehgal et al. , 2009 ).…”

Expression ofSHOOT MERISTEMLESS,WUSCHEL, andASYMMETRIC LEAVES1Homologs in the Shoots of Podostemaceae: Implications for the Evolution of Novel Shoot Organogenesis

“…Likewise, the floral meristem arises between and under the two youngest bracts endogenously and involves vacuolated cell detachment ( Figure 1F). However, a cupular envelope (spathella: a floral organ unique to Podostemoideae) and other floral organs (tepals, stamens, and pistil) develop in an ordinary (exogenous) manner from a conventional floral meristem (Figures 1C and 1F;Katayama et al, 2008;Sehgal et al, 2009).…”

Developmental biology of dispersed pollen grains

“…India has 10 genera and 28 species and most of them are endemic, and confined to Kerala and Karnataka (Khanduri et al, 2015). So far, pollination biology of six Indian taxa of this family has been studied -Polypleurum stylosum (Khosla et al, 2000), Griffithella hookeriana (Khosla et al, 2001), Indotristicha ramosissima (Khosla and Sehgal 2009), Hydrobryopsis sessilis (Sehgal et al, 2009), Willisia arekaliana (Khanduri et al, 2014) and Zeylanidium lichenoides . The flowers are tiny in all the species and show autogamy.…”