Phylogeography and population structure of the putative relict Reedia spathacea F.Muell. (Cyperaceae)

Lineages which have persisted from Gondwana and remain restricted to mesic habitats with fragmented distributions are often considered relicts. Relictual taxa belong to formerly more common groups that have become isolated phylogenetically by extinction and/or geographically by changes in climate and habitat availability. The south-west region of Australia is a biodiversity hotspot containing flora that are Gondwanan in origin. Within this region are restricted remnants of mesic habitat that host taxa not found elsewhere, including the endemic sedge Reedia spathacea F.Muell. (Cyperaceae). The species is found in refugial peat swamps and was described as a relict in the process of being listed as critically endangered, based on its unique morphology and its shared habitat with known relicts. However, R. spathacea is poorly understood, not well documented, and its purported relictual status has not been addressed. This study investigates the Gondwanan relictual status of R. spathacea through the application of criteria distilled from the literature. These are, to assess restriction to habitat that is atypical of the region, phylogenetic distinctiveness, lineage age, and population dynamics. Utilising life-history and morphology data from R. spathacea, molecular phylogenetics and dating, population genetics and phylogeography, this study finds that the lineage Reedia belongs to is phylogenetically distinct, with a clear early divergence and originates from the Gondwanan landmass. Further, populations are found to be recently genetically isolated, likely a result of contraction into refugia. These data showed that R. spathacea met all criteria to be considered a Gondwanan relict. Implications of these findings are considered for the conservation of R. spathacea, as measures currently undertaken do not best serve the biology of the species. In particular, R. spathacea has characteristics suggestive of adaptation to fire, has more than one recruitment strategy, and is capable of invading refugial habitats, or outcrossing with existing populations. These aspects of Reedia are not currently taken into consideration, in favour of conservation measures to address threat and stochasticity. This study successfully demonstrates that the use of all criteria to assess relicts is applicable to taxa other than R. spathacea, and that a concerted effort to uniformly apply these criteria is needed to better understand purported relicts. This is important so that conservation is no longer only reflective of vulnerability but adequately addresses characteristics unique to relict