An unusual new species of Eremocaulon, a Neotropical woody bamboo genus, is here described and illustrated. Eremocaulon triramis occurs in dense ombrophilous forest and is apparently endemic to Espírito Santo state, Brazil. The diameter and indument of the culms, number of branches in the branch complement, and occurrence of two different forms of fimbriae on the foliage leaves allow this taxon to be recognized as distinct from its congeners, even in the vegetative condition. Reproductively, E. triramis differs from its congeners in having laminiferous subtending bracts in the pseudospikelets and four stamens. Illustrations, photos, a detailed description, comments on morphology, habitat, distribution, and conservation status are provided, as well as a key to all species of Eremocaulon.