Plants perennial; cespitose or loosely colonial, rhizomatous. Culms 35-150 cm, simple or branched. Leaves cauline; ligules membranous, ciliate; blades not pseudopetiolate, flat. Panicles open or contracted, sometimes becoming racemose distally; disarticulation above the glumes and between the florets. Spikelets 4-50 mm, laterally compressed, with 2-many florets, lower 1-4 florets sterile. Glumes 2, subequal, shorter than the spikelets, glabrous, (2)3-9-veined, acute to acuminate; lemmas glabrous, 3-15-veined, compressed-keeled, keels serrate or ciliate, apices acuminate to acute, entire (rarely bifid); paleas glabrous, gibbous basally, 2-keeled, keels winged, wings glabrous, scabrous, or pilose; lodicules 2, fleshy, cuneate, 2-4-veined, lobed-truncate; anthers 1; ovaries glabrous; styles 2; style branches 2, plumose, reddish-purple at anthesis. Caryopses 1.9-5 mm, laterally compressed, brown to reddish-black or black. x = 12. Name from the Greek chasma, yawn, and anthos, flower, presumably for the gaping glumes that expose the grain at maturity.

Chasmanthium, a genus of five species endemic to North America, grows primarily in the southeastern and south central parts of the United States. It was formerly included in Uniola, but it is now recognized as a distinct genus.

1.    Chasmanthium latifolium (Michx.) H.O. Yates
Broadleaf Chasmanthium

Culms to 150 cm, 2-4 mm thick at the nodes, rarely branched, leafy for 80% of their height. Sheaths glabrous; collars glabrous; ligules 0.7-1 mm, entire; blades (7)9-18(22) cm long, (4)10-22 mm wide, lanceolate-fusiform, usually glabrous, sometimes pilose adaxially. Panicles (8)10-25(35) cm, open, lax; branches nodding or drooping; axils of panicle branches sparsely pilose; pedicels 10-30 mm. Spikelets 15-40(50) mm long, 6-16(20) mm wide, with 6-17(26) florets, lower 1-3 florets sterile, fertile florets diverging to 45°. Lower glumes 4.2-9.1 mm, 5-7-veined; upper glumes 4.7-8.7 mm, 5-9-veined; calluses pilose; fertile lemmas 9-12.5 mm, straight, 11-15-veined, keels winged, wings scabrous to pilose their full length; paleas 4.6-7.7 mm; anthers (0.4)0.6-2.6(3.5) mm, the length varying within a spikelet. Caryopses 2.9-5 mm, enclosed, rarely exposed at maturity. 2n =48.

Chasmanthium latifolium grows along stream and river banks and in rich deciduous woods. It is the most widespread species of the genus, extending further west and east than any of the other four species. The map shows its verifiable range. Yates (1966b) reported seeing one specimen each from New Jersey, New Mexico, and Manitoba, but none of the specimens had clear locality information. In the absence of any further specimens from these regions, the locality data on these three specimens are regarded as probably erroneous.

Flowering in C. latifolium is sometimes cleistogamous.

2.   Chasmanthium nitidum (Baldwin) H. O. Yates
Shiny Chasmanthium

Culms 40-120 cm, to 1 mm thick at the nodes, rarely branched,leafy for 80% of their height. Sheaths glabrous; collars glabrous; ligules 0.2-0.3 mm, entire; blades 9-16(33) cm long, 4-7 mm wide, lanceolate-fusiform, glabrous adaxially. Panicles (9)12-17(29) cm, open, erect; branches ascending to divergent; axils of panicle branches scabrous; pedicels 0.5-2 mm. Spikelets 12-24 mm long, (8)9-12(15) mm wide, with (5)7-9(11) florets, lower (0)1(2) florets sterile, fertile florets diverging to 45°. Lower glumes 3.1-5 mm, 7-9-veined; upper glumes 3-4.6 mm, (5)7-9-veined; calluses glabrous; fertile lemmas 5.5-8.5 mm, straight, 9-11-veined, keels not winged, scabridulous toward the apices; paleas 5-7.5 mm; anthers 1.9-2.4 mm, the length invariant within a spikelet. Caryopses 2.4-3 mm, enclosed at maturity. 2n =24.

Chasmanthium nitidum grows along stream and river banks, roadside ditches, and the margins of low, moist woods in the southeastern United States.

3.   Chasmanthium ornithorhynchum Nees
Birdbill Chasmanthium

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.

4.   Chasmanthium sessiliflorum (Poir.) H.O. Yates
Longleaf Chasmanthium

Culms 60-150 cm, (1)2-3.5 mm thick at the nodes, unbranched, leafy for 40% of their height. Sheaths pilose; collars pilose; ligules 0.2-0.3 mm, entire; blades (15)20-50 cm long, 4.5-9.5(15) mm wide, linear-lanceolate, sparsely pilose adaxially. Panicles (9)20-70 cm, contracted or open, erect; branches tightly appressed or ascending to strongly divergent; axils of panicle branchesglabrous or scabridulous at the edges; pedicels 0.3-2.5(5) mm. Spikelets 4-10 mm long, 6-9 mm wide, with 4-7(8) florets, lower 1(2) florets sterile, fertile florets divergent to 80°. Lower glumes 1.2-2.7 mm, 3-5-veined; upper glumes 1.4-2.2 mm, 3-5-veined; calluses glabrous; fertile lemmas 3.5-5.9 mm, usually curved or irregularly contorted, 7-9-veined, keels not winged, apices scabridulous; paleas 2.8-4 mm; anthers (0.8)1.3-1.6 mm, varying in length within a spikelet. Caryopses 2-2.5 mm, exposed at maturity. 2n =24.

Chasmanthium sessiliflorum grows in rich woods, meadows, and swamps, especially on the coastal plain. It grows throughout most of the southeastern United States.

5.   Chasmanthium laxum (L.) H.O. Yates
Slender Chasmanthium

Culms 40-130 cm, to 1 mm thick at the nodes, unbranched, leafy for 50% of their height. Sheaths glabrous; collars glabrous; ligules 0.2-0.4 mm, entire; blades (8)15-35(40) cm long, 3-8(11) mm wide, linear-lanceolate, usually glabrous, sometimes sparsely pilose adaxially. Panicles (7)12-35(47) cm, contracted, erect; branches ascending to appressed; axils of panicle branches glabrous; pedicels 0.5-2.5 mm. Spikelets 4-9 mm long, 2-6 mm wide, with (2)3-5(7) florets, lower 1(2) florets sterile, fertile florets divergent to 45°. Lower glumes 1.3-3 mm, (1)3-5-veined; upper glumes 1.3-2.5 mm, 3-5-veined; calluses glabrous; fertile lemmas 2.9-4.5 mm, straight, 3-7-veined, keels not winged, apices scabridulous; paleas 2.3-3 mm; anthers 1.3-1.5 mm, the length invariant within a spikelet. Caryopses 1.9-2.2 mm, exposed at maturity. 2n =24.

Chasmanthium laxum is almost completely sympatric with C. sessiliflorum in the southeastern United States, growing in similar habitats but extending further into sphagnous stream heads, pine flatwoods, and pine savannahs. Yates (1966b) reported seeing putative, naturally occurring hybrids between C. ornithorhynchum and C. laxum along streams of the outer coastal plain of Mississippi and Louisiana. In general appearance, the hybrids resemble C. laxum, their most striking difference being the enlarged, sterile spikelets.