A contribution to the systematics of Xylopia (Annonaceae) in Southeast Asia
ABSTRACT. Herbarium and field study of Xylopia L. (Annonaceae) for the Flora of Peninsular Malaysia and the Flora of Thailand projects has clarified regional diversity patterns within this ecologically significant lowland rainforest genus. Two species groups represented within Southeast Asian floras are delineated, one centred on Xylopia ferruginea (Hook.f. & Thomson) Baill. and the other on Xylopia malayana Hook.f. & Thomson. In the Xylopia ferruginea group, a new species, Xylopia erythrodactyla D.M.Johnson & N.A.Murray, is distinguished from X. ferruginea, and a new combination, Xylopia sumatrana (Miq.) D.M.Johnson & N.A.Murray, is proposed, based on an earlier name for the species currently known as Xylopia stenopetala Oliv. In the Xylopia malayana group, review of the species Xylopia elliptica Maingay ex Hook.f. & Thomson resulted in the recognition of three additional species: Xylopia platycarpa D.M.Johnson & N.A.Murray, from southern Thailand and northwestern Peninsular Malaysia, Xylopia ngii D.M.Johnson & N.A.Murray, from Peninsular Malaysia, Sumatra and Borneo, and Xylopia heterotricha D.M.Johnson & N.A.Murray, from Sumatra and Borneo. The taxon Xylopia malayana Hook.f. & Thomson var. obscura Kochummen is placed in synonymy under Xylopia elliptica sensu stricto. Xylopia fusca Maingay ex Hook.f. & Thomson var. sessiliflora Kochummen & Whitmore is distinguished from Xylopia fusca, and raised to species status as Xylopia sessiliflora (Kochummen & Whitmore) D.M.Johnson & N.A.Murray. We recognise 23 Xylopia species in the Sundaic region of Southeast Asia, and provide evidence that additional collecting and taxonomic analysis in the region is needed.