Distribution, abundance, ecology and management of the limestone Geranium socolateum (Geraniaceae) Heenan et Molloy

Limestone ecosystems provide habitat for several endemic, calcicolous, herbaceous plants, many of which are threatened. South Canterbury, Te Wai Pounamu / South Island, Aotearoa / New Zealand has at least six such taxa. This study surveyed limestone habitats in South Canterbury for one of these taxa, the limestone geranium Geranium socolateum. At the time of its taxonomic description in 2019, a threat status of Threatened / Nationally Critical was proposed using the 2008 iteration of the New Zealand Threat Classification System. In 2024 this was changed to Threatened / Nationally Vulnerable by the New Zealand Indigenous Vascular Plant Threat Listing Panel. These assessments have been based on limited data about the range, distribution and population sizes of the species. This paper reports on a study that found a wider geographical range and higher number of plants in sub-populations and overall than was known previously. The majority of the field work was carried out between 2019 and 2022 and recorded 6,330 plants of G. socolateum in 28 subpopulations in South Canterbury and two in North Otago. It is estimated that about 4,835 of these records were mature plants. Thus, the data supports the current threat ranking of Nationally Vulnerable for G. socolateum.