Plants perennial. Culms 30-100 cm tall, 3-6 mm thick, spongy, usually decumbent and rooting at the lower nodes. Sheaths smooth, weakly keeled; ligules 5-9 mm; blades 10-15 cm long, 3-8 mm wide, abaxial surfaces smooth, adaxial surfaces of the midcauline leaves often papillose. Inflorescences often racemes, sometimes panicles, 15-35 cm long, 1-2 cm wide, open at anthesis, bases often enclosed in the flag leaf sheaths at maturity; branches 5.5-8 cm (absent in racemose plants), solitary or in pairs, appressed, most branches with 1-3 spikelets, the lower branches sometimes with more than 3; pedicels 1.5-2.5 mm. Spikelets 20-45 mm long, 2.5-3 mm wide, cylindrical and terete except slightly laterally compressed at anthesis, rectangular in side view, with 5-12 florets. Glumes unequal, acute; lower glumes 1.3-4.5 mm; upper glumes 3-7 mm; rachilla internodes 2-3 mm; lemmas 6-8.5 mm, scabridulous, 7-veined, gradually tapering from near midlength to the narrowly acute (< 45°) or acuminate apices; paleas 0.7-3 mm longer than the lemmas, keels winged, tips parallel, intercostal region truncate, often splitting, apices appearing bifid, with 0.4-1 mm teeth; anthers 3, 1-2 mm. Caryopses about 3 mm. 2n = 40.
Glyceria acutiflora grows in wet soils and shallow water of the northeastern United States, extending from Michigan and Missouri to the Atlantic coast between southwestern Maine and Delaware. Its long paleas make G. acutiflora the most distinctive North American species of sect. Glyceria.
From Flora of Indiana (1940) by Charles C. Deam
In 1919 I found this grass in an artificial pond in Harrison County. The pond was revisited in 1935 and this species was still a common plant in it. R. M. Kriebel found it in 1934 in a sinkhole on the farm of Julius Blackwell, about two and a half miles northeast of Springville, Lawrence County. On July 29, 1935, he found about a half acre in a buttonbush swamp of about three acres on the Cobb farm about two miles northeast of Avoca, Lawrence County. Here it was associated with Cephalanthus occidentalis, Populus heterophylla, Rosa palustris, Glyceria septentrionalis, and Ranunculus flabellaris.
Culms to 1 m, usually decumbent and often rooting from the lower nodes; lvs 3-6 mm wide; ligule 5-7+ mm; infl erect or declined, narrow, 2-3 dm, the branches erect, strongly flattened or trough-shaped; spikelets 2-4 cm, 5-12-fld; glumes narrowly ovate, the first 2-3.3 mm, the second 3.9-5.6 mm; lemmas lanceolate, 7-8.5 mm, acute, scabrous; palea acuminate, 2-toothed, projecting 1.5-3 mm; rachilla-joints 3-4 mm; stamens 3; 2n=20, 40. Shallow water or very wet soil; Me. to Del., Va., and Tenn., w. to Mich. and Mo.; also in e. Asia.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.