Reproductive ecology of medicinally important Kashmir Himalayan species of Digitalis L.

Abstract

Reproductive biology, encompassing phenology, floral biology, pollination and breeding systems, was investigated in three pharmaceutically important and anthropogenically exploited species of Digitalis in the montane habitats of the Kashmir Himalaya. Flowers in all three species (Digitalis purpurea, Digitalis grandiflora and Digitalis lanata) are aggregated in racemes. Corollas are characteristically bell shaped enclosing four, didynamously arranged stamens. The stigma is deeply bifid only in D. purpurea. The three species over-winter as underground tubers and sprouting during the following spring occurs first in D. lanata, followed by D. purpurea and D. grandiflora. Floral bud opening in an inflorescence in all three species occurs sequentially from the bottom upwards in an acropetal succession and male and female phases are temporally separated with basal flowers entering the male phase first followed by the upper flowers in a regular sequence. Only after shedding the pollen grains completely do the flowers shift to the female phase. Resource allocation in all three species is more towards maleness than femaleness during anthesis. The species are principally insect pollinated and selfing is denied because of protandry and spatial separation of the stigma and anthers. Copious amounts of viable pollen grains produced by these species aid in successful pollination, fertilization and seed production. Studies revealed that none of these species operates autogamy because hand-pollinated flowers with self-pollen or bagged flowers (foreign pollen excluded) failed to set seed. High seed output in open-pollinated flowers and high pollen-ovule ratios also indicate the outbreeding nature of these species. Thus, any reduction in the number of individuals constituting a population would significantly reduce the floral display and consequent rewards to the pollinators, with a subsequent influence on seed roduction. Hence, data on the reproductive biology of overexploited species, such as Digitalis spp., is of pivotal importance in formulating effective conservation strategies.© 2008 The Society for the Study of Species Biology.