A Revision of Sumatroscirpus (Sumatroscirpeae, Cyperaceae) with Discussions on Southeast Asian Biogeography, General Collecting, and Homologues with Carex (Cariceae, Cyperaceae)

For over 40 yr, Sumatroscirpus (Sumatroscirpeae, Cyperaceae) has been treated as a monospecific genus endemic to the Indonesian island of Sumatra. This genus possesses sheathing fertile prophylls that have recently been shown to be homologous with the perigynia of Carex, its highly diverse sister-group (>2000 species, Cariceae). In this taxonomic revision, we recognize four species in Sumatroscirpus and extend its range into Vietnam, Myanmar, and Southwestern China.We divide the genus into two sections: 1) Sumatroscirpus sect. Sumatroscirpus, characterized by a cespitose habit, green leaf sheaths, large dense inflorescences, and long perianth bristles with dense antrorse barbs; and 2) Sumatroscirpus sect. Paniculatocorymbosi comb. nov., characterized by a rhizomatous habit, red leaf sheaths, small open inflorescences, and reduced perianth bristles with few to no barbs. Sumatroscirpus junghuhnii, Sumatroscirpus minor comb. nov., and Sumatroscirpus rupestris sp. nov., are placed in Sumatroscirpus sect. Sumatroscirpus. The distinctive Sumatroscirpus paniculatocorymbosus is placed in Sumatroscirpus sect. Paniculatocorymbosi. A lectotype is designated for Scirpus junghuhnii var. minor, the basionym of Sumatroscirpus minor. Identification keys to Cyperaceae tribes possessing fertile prophylls, and to Sumatroscirpus species, are provided,with descriptions, illustrations, distributionmaps, and conservation status assessments for each species. We make a detailed account of the inflorescence morphology of Sumatroscirpus, with special reference to the perigynium. In light of our results, we highlight the importance of herbaria and general collecting for species discovery and conservation. We also discuss the biogeography of Sumatroscirpus, which illustrates a well-known biogeographic link between the Sino-Himalayan and Sundaland mountain floras.