Pollination ecology and breeding system of Justicia gendarussa Burm. f. (Acanthaceae): first report of fruit set through supplementary obligatory-xenogamous pollination.

Justicia gendarussa Burm. f. (Acanthaceae) is a highly important medicinal plant restricted to tropical Asia. However, recently, the species has become rare in different states of India, including West Bengal. To unravel its conservation status, the present study investigates the different reproductive aspects (flower biology, floral rewards, floral volatiles, floral visitors, and breeding system) for its long-term sustenance. The plant blooms once a year (January to April), with steady-state flowering. Flowers are typically gullet-shaped and have a longevity of 4 days. The male phase (day 1 to day 3; pollen fertility = 82.45 ± 2.14%) coincides with the female phase (day-2 to day-3), indicating dichogamy. The creamy white corolla with purple spots, floral nectar, and floral volatiles attract different groups of floral visitors. However, bees and syrphid flies are potent pollinators. As per pollination efficiency (PEi) and relative pollination service (RPS), Amegilla zonata is the most efficient pollinator (PEi = 0.86) and the only representative of the primary pollinating group (RPS% = 66.28). The plant species is completely self-incompatible (ISI = 0); obligatory xenogamy is the only successful pollinating mode. Thus, the plant species is completely pollinator dependent. The coefficient of pollination deficit is maximal in the wild habitat ( D= 1). Increasing population density of the potent pollinators and habitat (germplasm) conservation may be the most effective strategy for the long-term sustenance of this plant species.