Reproductive strategies in the rare and endangered Killickia grandiflora (Lamiaceae) – implications for its urgent conservation

Abstract

Populations of rare and restricted species are commonly challenged due to risks associated with reduced genetic diversity, environmental variation, and demographic stochasticity. Killickia grandiflora (Lamiaceae) is one of three Killickia species endemic to the Drakensberg Mountain Centre in KwaZulu-Natal, South Africa. Its confirmed distribution is restricted to a firebreak between two catchments in the Cathedral Peak region of the Ukhahlamba Drakensberg Transfrontier Park, where it is threatened by habitat transformation. In this study, we aimed to understand factors that promote or inhibit gene flow within this highly restricted K. grandiflora population, to estimate inbreeding, and to assess its status as a potentially threatened species. Exclusion and hand pollination trials indicate that K. grandiflora cannot autonomously self-pollinate and is dependent on pollinators for outcrossing. Germination trials and tetrazolium staining suggest that the seeds may have dormancy breaking requirements or are inviable. Inbreeding and genetic diversity analyses show that the K. grandiflora population nonetheless maintains a high level of genetic diversity, likely through outcrossing, despite the small population size and apparent poor reproductive success. We recommend that the IUCN conservation status of K. grandiflora be changed from Vulnerable to ‘Critically Endangered’ based on observed reductions in population size, limited extent of occurrence, small number of mature individuals, and threats by woody competitors. We strongly recommend that the known population(s) be monitored and the habitat patches be conserved regardless of size and maintained through regular burning to enable the species’ survival and conservation. Ex situ propagation and reintroduction to its historical habitat should be explored as additional conservation measures for this species.