Henrik Balslev

Geonoma atrovirens and G. supracostata (sect. Taenianthera) (Arecaceae) from the western Amazon are described and illustrated. Both species are described on material hitherto included in the widespread G. macrostachys s.l., a species complex of understory palms represented in most parts of the Amazon region. Geonoma atrovirens resembles entire-leafed forms of Geononia macrostachys var. macrostachys but differs form that taxon in having extremely narrow, bluish green leaves, and a different structure of its staminate flowers. Geonoma supracostata differs from all forms of G. macrostachys in the combination of an usually well developed aerial stem and moderately dissected leaves with the veins sharply raised alternately on the adaxial and the abaxial side of the lamina. A key to the species of Geonoma sect. Taenianthera in the western Amazon is provided.