Testing species limits in 'Rennellia' (Prismatomerideae, Rubioideae, Rubiaceae)

Previous studies of 'Rennellia', 'Gentingia', 'Motleya'and 'Prismatomeris' resulted in conflicting classifications. This first phylogenetic analysis of these genera, based on morphological data, supports their separation from Morindeae s.str. as members of Prismatomerideae. Transfer of 'Prismatomeris subsessilis' King & Gamble to 'Gentingia subsessilis' (King & Gamble) J.T. Johansson & K.M. Wong is supported. Monotypic 'Motleya' is nested in the 'Prismatomeris' clade. 'Rennellia paniculata' King & Gamble var. 'paniculata' K.M. Wong and 'R. paniculata' King & Gamble var. 'condensa' K.M. Wong are monopyletic. There is no support for 'Rennellia morindiforms' (sensu Johansson) or 'R. elliptica' (sensu Johannson). 'Rennellia' sp. (Fraser's Hill) is possibly conspecific with 'R. morindiformis' (Korth.) Ridl., and 'R. borneensis' (Baillon) Ridl. and 'R. elongata' (King & Gamble) Ridl. with 'R. elliptica' Kirth. The relationships of 'Rennallia morindiformis' (Korth.) Ridl., and 'R. borneensis' (Baillon) Ridl. and 'R. elongata' (King & Gamble) Ridl. with 'R. elliptica' Korth. The relationships of 'Rennellia microcephala' (Ridl.) K.M. Wong and 'R. amoena' (Bremekamp) J.T. Johansson are poorly resolved. Complete resolution was not obtained probably due to a lack of good quality collections, particularly of 'Rennellia'. The pressing priority is for fieldwork to obtain high quality specimens to allow molecular studies and comprehensive morphological investigation, to further test species limits and resolve relationships within and among these genera.