Small carpgrass (Arthraxon hispidus) is also commonly confused with Oplismenus hirtellus ssp. undulatifolius. A. hispidus is annual, invasive grass that was introduced into the United States, either accidentally or by immigrants, from Japan and eastern Asia. The plant stands to 0.5 m tall with oval to lance-shaped leaves. Leaves are 2.5-7.6 cm long, 0.5 cm wide and have heart shaped bases. The margins of the leaves have conspicuous hairs. Flowers bloom in early fall and are contained in 1 to several 2.5-7.6 cm long spikes. Small carpgrass inhabits wet areas such as stream banks, flood plains and shoreline of eastern and central United States. It does not have wavy leaves like O. hirtellus ssp. undulatifolius (Invasive.org, 2010; Kerrie Kyde, pers. comm., 2010; USDA-NRCS, 2010)
annual jewgrass (English), Asian stilt grass (English), bamboo grass (English), Chinese packing grass
(English), flexible sesagrass (English), Japanese grass (English), Japanese stilt grass (English), Mary's grass (English), Nepal grass (English), Nepal microstegium (English), Nepalese browntop (English), Vietnamese stilt grass (English)
Japanese stiltgrass, Microstegium vimineum looks similar to and occurs in the same habitats as Oplismenus hirtellus ssp. undulatifolius. M. vimineum differs from O. hirtellus ssp. undulatifolius in that it has glabrous culms, smooth unrippled leaf blades, a single stripe of silver hairs along the midribs, and blunt gradually pointed leaf tips. The two grasses can be observed growing side by side in Maryland (USA), but little to no intermingling has been observed. O. hirtellus ssp. undulatifolius is perennial, remains green later in the season, has a highly effective seed dispersal mechanism, and appears to be more competitive than M. vimineum, making it more potentially invasive (Kyde & Marose, 2008).