Abstract
The genus Chassalia (Gentianales: Rubiaceae-Palicoureeae) in Borneo is revised based on a morphological survey of herbarium specimens using classical taxonomic methods. The tribal placement and probable paraphyly of Chassalia as currently delimited is reviewed. Previously, four described species of Chassalia were known from Borneo, with only one endemic species, Chassalia psychotriformis I.M.Turner nom. nov. (≡ Cephaelis psychotrioides Valeton). A key is given to the 18 species of the genus recognised from Borneo in this study. In total, 14 new species are described, all of them endemic to Borneo. These are: Chassalia atropurpurea T.Y.Yu sp. nov., Chassalia beamanii T.Y.Yu sp. nov., Chassalia calamus T.Y.Yu sp. nov., Chassalia chewii T.Y.Yu sp. nov., Chassalia involucrata T.Y.Yu sp. nov., Chassalia kinabaluensis T.Y.Yu sp. nov., Chassalia lancifolia T.Y.Yu sp. nov., Chassalia lancifolioides T.Y.Yu sp. nov., Chassalia longipes T.Y.Yu sp. nov., Chassalia macrocarpa T.Y.Yu sp. nov., Chassalia muluensis T.Y.Yu sp. nov., Chassalia muscicola T.Y.Yu sp. nov., Chassalia northiana T.Y.Yu sp. nov. and Chassalia ramosa T.Y.Yu sp. nov. Circumscriptions and discussions are given for all Bornean species recognised. A morphological glossary for Asian species of Chassalia is provided. Three separate species groups are recognised, the Chassalia curviflora and C. javanica groups, represented by a single species each in Borneo, and a new informal group, the ‘Involucrate group’, which is proposed and circumscribed to encompass the majority (16) of the Bornean species. Proposals for further work on Asian Chassalia are given.
Highlights
The genus Chassalia Comm. ex Poir. is placed in subfamily Rubioideae tribe Palicoureeae (Robbrecht & Manen 2006) of the pantropical family Rubiaceae (Razafimandimbison et al 2008)
The morphological characters that are used traditionally to differentiate Chassalia from related genera in the Palicoureeae include the presence of corky stipules, flowers usually sessile in capitula, corolla tube usually long, sometimes curved or winged (Bremekamp 1962; Verdcourt 1976)
We present our study as a first step towards revising the genus on the island of Borneo
Summary
The genus Chassalia Comm. ex Poir. is placed in subfamily Rubioideae tribe Palicoureeae (Robbrecht & Manen 2006) of the pantropical family Rubiaceae (Razafimandimbison et al 2008). The genus Chassalia contains about 120 accepted species, the majority of which are from Africa and Madagascar (Turner 2019). Most species of this genus are erect shrubs and shrublets, sometimes monopodial, or small trees, but several species in West and Central Africa are stem-twining climbers and a few species are epiphytic (Cheek et al 2004). The morphological characters that are used traditionally to differentiate Chassalia from related genera in the Palicoureeae include the presence of corky (indurated) stipules, flowers usually sessile in capitula, corolla tube usually long, sometimes curved or winged (Bremekamp 1962; Verdcourt 1976)
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