Taxonomic status, distribution and conservation of the Critically Endangered plant Psychotria angustata (Rubiaceae), endemic to Floreana Island, Galapagos

Abstract

Two species of Psychotria have been recognised in the Galapagos Islands, both understorey shrubs endemic to the archipelago: P. rufipes Hook. f. occurs on seven islands, including Floreana, while P. angustata Andersson is endemic to Floreana. Since their mid-19th century discovery, the taxonomic and ecological status of these species has been uncertain. To clarify this, we examined historical specimens and numerous recent collections of both species, and surveyed their distribution on Floreana. Examination of the original description of P. angustata enables restriction of its type to the single specimen Andersson 195, which we designate the lectotype. We found differences in leaf venation, indumentum, shape and size, which confirm the existence of two clearly different forms that were originally referred to two species. Where these occur together no intermediate individuals were found. Differences also exist in the indumentum of twigs, inflorescences and flowers, but flower colour appears to be similar (white to cream) in the two taxa. These differences are of a degree commonly treated as infra-specific in other species of Psychotria. We conclude that the two taxa hitherto recognised as species are better regarded as varieties within P. rufipes and provide the consequent new combination Psychotria rufipes var. angustata W. Simbaña & Tye stat. nov. Both taxa are threatened by humid forest destruction and introduced animals and plants. Surveys confirm the global Red-List status of P. rufipes var. angustata as Critically Endangered. Population age structure indicates regeneration of both taxa since the recent eradication of feral ungulates from Floreana, but invasive plants still threaten them.