Black Fountaingrass (U.S. National Park Service)

Three photo collage of black fountain grass plant with fuzzy yellow seedheads on left, flowerhead with seeds in middle, and closeup of spikelets on right. — Black fountaingrass. Left to right: entire plant, flower head with seeds, and close-up of spikelets.
Left to right: entire plant Emily Summerbell (CC BY); flower head with seeds, pppepper (CC BY-NC); and close-up of spikelets, Emily Summerbell (CC BY); iNaturalist

What’s this fuzzy-looking flowerhead? Black fountaingrass (Cenchrus purpurascens) is an invasive plant that is also a popular ornamental grass due to its red-to-purple-colored flowerhead. It can be found in plazas and housing complexes throughout the greater Washington, DC area that we call the National Capital Region (NCR).

Black fountaingrass spreads quickly. Bristles that stick outward and whorl around the seed, making it easy to attach to fur, clothes, and shoes, and adhere to passersby. They can also spread by birds, wind, water, and mowing.

Two photo collage of black fountaingrass showing whole green grassy clump on left and a hand holding one flattened stem of grass on right. — Black fountaingrass. On left, the whole plant with no flowers and on right, the fan-like shape of a singular stem with white lines at the base of the leaf.
Left image Steve Young (CC BY), iNaturalist. Right image Yvonne Ng (CC BY-NC)

While black fountaingrass was initially thought to be an Early Detection and Rapid Response species, the NCR Invasive Plant Management Team (IPMT) quickly realized how well-established the grass is throughout NCR. In autumn of 2023, large infestations of black fountaingrass were reported, especially along C&O Canal and Rock Creek. IPMT focused their efforts on monitoring black fountaingrass throughout NCR parks and reducing seed production using herbicide treatment. Volunteers also helped by surveying along Rock Creek and cutting off flowerheads. During the 2024 field season, IPMT has seen great improvements in where black fountaingrass was previously treated.

Two photo collage of black fountaingrass infestation. One left black grass seedheads arch towards a water filled canal. One right a clump of grass with dark seedheads grows next to a shallow creek — Black fountaingrass. Small infestations at C&O Canal on left and at Rock Creek Park on right.
Left: Michael Inlow (CC BY_NC). Right: Yvonne Ng (CC BY-NC)

How to Identify Black Fountaingrass

Black fountaingrass is a perennial grass. The bristles on the flowerhead can range from green to purple from summer through early fall (Brookman, 2015; Flora of China n.d.). Like most grasses, black fountaingrass is most easily identified when in flower or seed.

Characteristics to look out for:

Clumpy and grows up to 3 feet tall
Leaves are flattened along the stem and branch out, forming a shap similar to an elongated fan
Smooth, white line and hairs are present where leaf blade meets the stem
Resistence when gliding fingers from leaf tip toward the stem
Hairy flowerhead stem
Generally found along waterways, wet to moist soils, and floodplains, but can also be found in dry lawns around the region

Look-alikes

Native bottlebrush grass (Elymus Hystrix)

Two photo collage of bottlebrush grass seedheads. On left erect grass stalks in woodland setting and on right looking down at grass seedhead with protruding hairlike structures. — Native Bottlebrush grass. Two views of flowerhead featuring two spikelets in opposite arrangement.
Left: mefisher (CC0). Right: Jim Bowhay (CC0); iNaturalist.

The native bottlebrush grass (Elymus hystrix) is another grass with a similar flowerhead to black fountaingrass. Here are some ways to tell the differences between the two:

Black Fountaingrass (Invasive)	Bottlebrush Grass (Native)
Arches	Stands erect
Green to purple flowerhead	Ranges between pale to bright green
Inconsistent arrangement of spikelets	2 spikelets alternating along the stem
Numerous bristles whorl around spikelet	2-4 bristles on spikelet
Found along waterways and sunny dry habitats	Found in shady, dry, upland habitat

Two images compare thin stalks of grass. On left a small black claw seems to point up from leaf collar. On right the leaf collar appears white and rounded. — Comparison of (Left) native bottlebrush grass leaf collar and (Right) black fountaingrass leaf collar
Left: Adam Kranz (CC0). Right: davidenrique (CC BY-NC-SA); iNaturalist.

Several native grasses in our region have this bottlebrush flowerhead, but none of them have the purple color that black fountaingrass has. This makes the non-native grass distinct during the flowering period.

Tips for making a good observation record of black fountaingrass

Take photographs that show:

Area where they were found
Infestation/population
Numerous photos of the whole plant that include the flowerhead
If flowerheads not present, then provide a closeup of the flattened leaves

Make comments that:

Explain whether the plants are intentional or wild
Give a rough estimate of the number of plants and the area covered

References

Brookman, Susan. 2015. Pennisetum alopecuroides/NJ. Retrieved 8/16/23 from https://wiki.bugwood.org/Pennisetum_alopecuroides/NJ \
Flora of China. n.d. Pennisetum alopecuroides. Retrieved 9/10/24 from efloras.org/ florataxon.aspx?flora_id=2&taxon_id=200025851
Lee, M.T. 2023. Cenchrus purpurascens. Flora of Southeastern United States by North Carolina Botanical Garden. Retrieved 8/16/23 from https://fsus.ncbg.unc.edu/show-taxon-detail.php?taxonid=2232
NCU Extension. n.d. Cenchrus alopecuroides. Retrieved 8/16/23 from https://plants.ces.ncsu.edu/plants/cenchrus-alopecuroides/
NCU Extension. n.d. Elymus hystrix. Retrieved 8/16/23 from https://plants.ces.ncsu.edu/plants/elymus-hystrix/