New Invader Waves a Red Flag

Contact: K. L. Kyde, Maryland Department of Natural Resources

Wavyleaf basketgrass in Little Paint Branch Park, Prince George’s County. Photo: K. L. Kyde

ANNAPOLIS, MD (August 6, 2007) – Two small populations of a Eurasian grass never previously found in the US were discovered in Patapsco State Park by sharp-eyed botanists in 1997. Smithsonian Institution experts confirmed its identity as an exotic species of a grass that is native to sub-tropical and tropical regions, including the southeastern coast of the US. The native species is Bristle basketgrass (Oplismenus hirtellus); the exotic species is Wavyleaf basketgrass (Oplismenus undulatifolius). In 2000, a private consulting ecologist found this grass by a wooded stream on the property of the Hernwood Landfill in Baltimore County. Last year this shade-tolerant moist forest grass turned up more than 20 miles away in Little Paint Branch Park in Prince George’s County, where it is being actively removed by groups of volunteers led by Dr. Marc Imlay of the Anacostia Watershed Society and Maryland-National Capital Park and Planning Commission (M-NCPPC) staff. During this dry summer, this fast-moving grass is one of the few plants obvious on the forest floor, even though it hasn’t yet bloomed, and so has been selected as the Maryland Invasive Species Council’s August Invader of the Month.

Wavyleaf basketgrass is a striking grass. It is a low-lying, trailing perennial grass, branching and rooting at the lower stem nodes. The leaf blades are flat, about ½” wide and between 1½ and 4” long, deep green with rippling waves across the grass blades, as though the tide were coming into shore along the leaves. The leaf sheaths and stems are noticeably hairy, although the hairs are very short. This characteristic distinguishes it from its closest relative Oplismenus hirtellus ssp. setarius, which occurs naturally in the southeastern US and Mexico and has only a few hairs, if any. When it blooms, in late September and into October, the grass spikelets have glumes (lower bracts) with very long awns (extended pointed tips). The awns produce a sticky substance that allows the grass seed to adhere to passing animals and so disperse.

It is unclear how Wavyleaf basket grass first came to the US and to Maryland, although it is possible that the Baltimore County landfill was the unwitting source of the natural area infestation, spreading from hanging basket plantings that someone threw away. Variegated varieties of the related O. hirtellus ‘Variegatus’ are sold ornamentally as “Ribbon grass” or “basket grass,” but the wavyleaf species does not seem to be sold in the horticultural trade. It does appear to spread rapidly through wooded natural areas: the Little Paint Branch pockets of infestation add up to about 3 acres.

Wavyleaf basketgrass may be a very good candidate for Early Detection – Rapid Response. The Maryland populations are still small, though spreading, and the grass can be removed successfully either by hand-weeding or by treating with 1-2% glyphosate, according to the work done so far in Little Paint Branch Park. No studies are available of its impact on native species or natural areas ecosystems. Its cousin, O. hirtellus, although native in the southeastern US, is considered invasive and a threat to endangered plant species in Hawaii by the US Fish and Wildlife Service. Should we remove a Eurasian grass species just because it is not from here? Or because it has been observed to be invasive, but hasn’t been proven so? If we let it go for several years to see what it does in riparian forests, are we risking a problem similar to that created by Japanese stiltgrass? Scientists revisiting the original detection sites 10 years later to assess spread rate will be able to make that decision.

For questions or comments, or if you have seen this grass, please contact:
K. L. Kyde, Maryland Dept. of Natural Resources

For more information about other Invasive Species of Concern, visit the Maryland Invasive Species Council.