Monoecy, anemophily, anemochory and regeneration ecology of Hildegardia populifolia (Roxb.) Schott. and Endl. (Malvaceae), an economically important endemic and endangered dry deciduous tree species of southern Eastern Ghats, India

Abstract

Hildegardia populifolia is a critically endangered tree species. All phenological events—leaf flushing, shedding, flowering, fruit dispersal occur one after the other during the dry season. It is morphologically andromonoecious but functionally monoecious. It produces a strikingly male-biased male and bisexual flower ratio; it is self-incompatible and obligately outcrossing. The flowers are nectariferous and the nectar has hexose-rich sugars, some essential and non-essential amino acids. Trigona bee and Rhynchium wasp were the exclusive foragers, though their foraging activity does not promote cross-pollination. The male flower number, the pollen output, the pollen characteristics and the placement of anthers on the top of androphore conform to anemophily. The natural fruit set does not exceed 5%. The fruit is 5-follicled with one or two seeds. The low fruit set is compensated by the production of more 2-seeded follicles. Fruit characteristics such as wing-like follicles, membranous follicle sheath and being very light weight characterize anemochory. Seeds with a hard coat do not germinate readily during the rainy season and their germination depends on the soil chemicals and nutrient environment. The soil is deficient in nitrogen, potassium and phosphorous. Partly burned seeds due to natural or human-caused fires germinate quickly in water saturated soil. The study suggests that seed germination and seedling growth rates are regulated by intrinsic and extrinsic factors along with natural and anthropogenic fires. We recommend that seedlings should be raised in nurseries and then transferred to natural habitats to build up the population.