Genetic and morphological analyses support the reinstatement of Schoenus vacillans (Cyperaceae) as distinct from S. apogon

Schoenus vacillans is a sedge described from New Zealand in 1878 by Thomas Kirk. However, for over one hundred years, S. vacillans has been considered a synonym of the morphologically-variable S. apogon, which occurs in New Zealand, Australia, Taiwan, New Guinea and possibly Japan. Here we investigate the taxonomic status of S. vacillans by examining chloroplast and nuclear DNA sequences alongside morphology. Our analyses showed that S. vacillans and S. apogon are genetically distinct and are not sister taxa. Furthermore, S. vacillans is easily distinguished morphologically from S. apogon by its diffuse, many noded but few flowered inflorescences. Our results indicated that S. vacillans should be reinstated at species rank. Furthermore, it appears to be endemic to New Zealand and not conspecific with the Australian S. laxiflorus Steud., another putative segregate of S. apogon. Herbarium records indicate a distribution of S. vacillans from the central North Island northwards but there are few recent records and known populations are small. We suggest a threat ranking of Nationally Critical, with a Data Poor qualifier. Schoenus vacillans appears to prefer shady, damp sites on the sides of gullies and banks, particularly on slips.