Essential dependence on wild pollination service: a medicinal plant under threat Minthostachys verticillata (Lamiaceae)

Abstract

Minthostachys (Benth.) Spach (Lamiaceae) is one of the most important genus in Andean folk medicine. Minthostachys species are harvested in the wild rather than cultivated. Beyond the key socio-cultural role of these species, there have been no studies to evaluate their reproductive requirements as part of their conservation. M. verticillata is a gynodioecious species endemic from Argentina, whose populations are threatened because of overexploitation and habitat loss. The level of reproductive dependence on animal pollination, the diversity and composition of floral visitors’ assemblages, flower morphology, fruit and seed set and the progeny vigour of female and hermaphrodite plants were evaluated. Both sex morphs rely absolutely on animal pollination for seed production and were visited by a similar and diverse assemblage of insects (Diptera, Lepidoptera and Hymenoptera); however, the tachinind fly Ptilodexia cf. cingulipes was the main pollinator. Female plants have smaller flowers, higher fruit set, fruits with more seeds, and a higher percentage of seed germination than hermaphrodites. There were no differences in growth rate and biomass of seedlings produced by female and hermaphrodite plants. Lower reproductive success of hermaphrodites could be due to self-incompatibility or inbreeding depression. These results suggest that it is a fragile system where hermaphrodite plants perform mainly as pollen donors, females as seed producers, and seed production relies almost exclusively on a native tachinid species, which is furthermore parasitoid. This knowledge can be applied in conservation programs in order to promote the sexual reproduction and so the conservation in situ of this key medicinal resource.