THE CIRCUMSCRIPTION, TAXONOMY AND BIOGEOGRAPHY OF PORTERANDIA (RUBIACEAE – GARDENIEAE)

Abstract

The taxonomic history of Porterandia (Rubiaceae) is reviewed. Its plant architecture and other morphological characteristics are compared with those of the related Atractocarpus and Bungarimba. Porterandia species are typically gynodioecious (and sometimes gynomonoecious), with sexual dimorphism in inflorescence form and flowers. Secondary pollen presentation in bisexual flowers is present. In a cladistic analysis using 34 morphological characters, Porterandia, Atractocarpus heterophyllus (type species of Atractocarpus) and Bungarimba were neatly polarised from Aidia, the outgroup. The 20 species of Porterandia in the analysis formed a well-supported monophyletic group, clearly delimited by primary and lower-order branches with terminal cymes in forks, stipules fused into a tube and with hairy inner surfaces, anisophyllous leaf pairs, corollas with stiff bristle-like hairs over the tube outer surface and adaxially hairy lobes. A revision enumerated 22 species of Porterandia, including a new species, P. dinghoui Zahid & K.M.Wong. Borneo, with 19 species, is the centre of diversity; outlying taxa appear to diverge from Bornean taxa in some characters; for example, Porterandia anisophylla and P. scortechinii (Sumatra, Malaya) are the only species with downward-pointing hairs on the corolla tubes (the rest have upward-pointing hairs), and P. celebica (Sulawesi) has atypical hood-like, fused (instead of free) inflorescence bracts. The northwest Borneo region has a significant species diversity and congregation. Extinction of Porterandia populations from heavily disturbed or open sites indicates that habitat conservation and the integrity of large forest patches and tree stands are critical.