Culms 35-40(90) cm, 0.8-1 mm thick at the nodes, rarely branched, leafy
for 80% of their height. Sheaths glabrous; collars pilose; ligules
0.2-0.3 mm, irregularly laciniate; blades 7-9(15) cm long, 3.5-6 mm wide,lanceolate-fusiform,
glabrous adaxially. Panicles (2.5)5-10.5(12) cm, open, erect; branches
divergent, sometimes strongly so; axils of panicle branches pilose; pedicels
0.5-1 mm. Spikelets 9.5-12 mm long, 11-17(18) mm wide, with (4)5-10 florets,
lower 2-4 florets sterile, fertile florets divergent to 85°. Lower glumes
2.5-2.9 mm, 2-3-veined; upper glumes 2.6-3.6 mm, 3-5-veined; calluses
glabrous; fertile lemmas 5.8-9.3 mm, straight, (9)11-13-veined, keels not
winged, scabrous to scabridulous distally; paleas 7.2-9 mm; anthers
1.1-1.9 mm, the length invariant within a spikelet. Caryopses 2-3 mm, enclosed
at maturity. 2n =24.
Chasmanthium ornithorhynchum grows along stream and river banks in low
woods, and on hummocks in swamps. It is most common along the coastal plain from
eastern Louisiana to western Florida, but is also found at a few other locations
in the southeastern United States.