Six New Species of Argomuellera (Euphorbiaceae) from Madagascar

Six new species of Madagascan Argomuellera Pax are recognized. Argomuellera bilocularis McPherson is unique in the genus in having a 2-locular ovary; A. gillespieae McPherson, restricted to the Manongarivo Massif, has leaves more than 6 cm wide and pistillate sepals less than 3 mm long; A. integra McPherson, from northern Madagascar, has small leaf blades (4-11 x 1-3.5 cm) with entire margins; A. longistipula McPherson, endemic to the VohEmar Region, has unusually long stipules (2-5[7] mm); A. oblanceolata McPherson, from western and southwestern Madagascar, has small acuminate leaves with dentate margins; and A. stenophylla McPherson, from southwestern Madagascar, has small, unusually narrow leaves (5-13 x 0.5-1.7[-2] cm). Argomuellera decaryana (Leandri) J. Leonard is relegated to the synonymy of A. perrieri (Leandri) J. Leonard. A key to the 12 Argomuellera species of Madagascar and the Comoro Islands is presented.