A new species of herbaceous bambusoid grass,Lithachne humilis, is described from Honduras and compared with the three other species known in the genus. As in many other grasses of this alliance, the leaves ofL. humilis exhibit so-called “sleep movements” at night. The diurnal and nocturnal positions of its leaves are compared to those ofStrephium distichophyllum. The leaves of the new species and of two of the others inLithachne hang down vertically at night, while those ofStrephium fold upward, which is the usual position assumed by leaves of bambusoid grasses during the night.