Ecological divergence in a carnivorous plant, Drosera indica L. (Droseraceae): discovery of a red-tentacled dwarf form adapted to drought stress

Carnivorous plants inhabit nutrient-poor environments and have evolved specialized mechanisms to capture and digest prey, resulting in a surprisingly diverse group of over 600 species. However, the ecological processes underlying their diversification remain insufficiently understood. We investigated two sympatric types of Drosera indica L. (Droseraceae) in southeastern Thailand: the RR type, characterized by red tentacles and dwarf growth, and the WR type, with white tentacles and taller growth. To examine factors associated with the divergence, we combined field observations with cultivation experiments to test three hypotheses: drought tolerance, herbivore defence, and pollinator protection. Field surveys showed that RR plants occurred predominantly in drier microhabitats with low soil moisture, whereas WR plants were restricted to wetter sites. Under dry cultivation conditions, RR plants exhibited higher survival than WR plants, supporting greater tolerance to drought. Herbivory rates did not differ significantly between the two types. In contrast, pollinator-trapping frequency was higher in RR plants, probably because dwarf growth reduces the spatial separation between flowers and traps. These findings indicate microhabitat-associated differentiation between the two types and suggest that adaptation to local moisture conditions may contribute to divergence within Drosera sect. Arachnopus.