Black fountaingrass (Cenchrus purpurascens) is planted on purpose. Its fuzzy, red-to-purple flowerheads make it a popular ornamental, and it grows in plazas and housing complexes across the greater Washington, DC area — the National Park Service's National Capital Region (NCR). It is also invasive, and it spreads fast.
How it gets around
The seed is ringed by a whorl of outward-pointing bristles that catch on fur, clothes and shoes, so it hitches a ride on whoever brushes past. Birds, wind, water and mowing move it too.
Bigger than first thought
The NCR Invasive Plant Management Team (IPMT) at first treated black fountaingrass as an Early Detection and Rapid Response species — one caught early enough to stamp out. It soon became clear how well established it already was. In autumn 2023, large infestations were reported, especially along the C&O Canal and Rock Creek.
The team's response was to monitor it across NCR parks and cut seed production with herbicide, while volunteers surveyed Rock Creek and snipped off flowerheads. By the 2024 field season, the team was seeing great improvements where the grass had been treated.
Telling it apart
A perennial grass, it is easiest to identify when in flower or seed, when the bristles run from green to purple, summer through early fall. Look for:
- clumps up to 3 feet tall;
- leaves flattened along the stem and branching out into the shape of an elongated fan;
- a smooth white line and hairs where the leaf blade meets the stem;
- resistance when you run your fingers from the leaf tip toward the stem;
- a hairy flowerhead stem;
- a home along waterways, wet to moist soils and floodplains — though it also turns up in dry lawns around the region.
The look-alike is native bottlebrush grass (Elymus hystrix). Several native grasses in the region have a bottlebrush flowerhead, but none has the purple color, which makes the invader distinct while it is in flower.
Native bottlebrush grass, with two spikelets in opposite arrangement. Left: mefisher (CC0); right: Jim Bowhay (CC0); iNaturalist.
| Black fountaingrass (invasive) | Bottlebrush grass (native) | |
|---|---|---|
| Habit | Arches | Stands erect |
| Flowerhead color | Green to purple | Pale to bright green |
| Spikelets | Inconsistently arranged | Two, alternating along the stem |
| Bristles | Numerous, whorled around each spikelet | 2–4 per spikelet |
| Habitat | Waterways and sunny, dry places | Shady, dry uplands |
Reporting it
A useful observation record has photos of where the plants were found, of the whole infestation, and of whole plants including the flowerhead — or, without flowerheads, a close-up of the flattened leaves. Add a note on whether the plants look planted or wild, and a rough count of plants and the area they cover.
Sources
Based on "Black Fountaingrass," National Park Service, National Capital Region Invasive Plant Management Team, which draws on Brookman (2015), the Flora of China, Lee (2023, Flora of Southeastern United States) and NC State Extension; a work of the United States government in the public domain. The bottlebrush grass photographs are dedicated to the public domain (CC0) by their photographers.
In these publicationsChesapeake & Ohio Canal National Historical ParkGeorge Washington Memorial ParkwayNational Capital Parks-EastPrince William Forest ParkPiscataway Park
Licence: CC0 1.0 (public domain) · Adapted from www.nps.gov
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