Plants rhizomatous or not; rhizomes, when present, thick, usually purplish-brown, scales closely imbricate. Culms to 120 cm tall, 1-3 mm thick, indurate, solitary or in small, dense clumps. Sheaths mostly glabrous, throats glabrous or short-pilose; ligules 0.5-1 mm; blades 8-56 cm long, 2-6(7) mm wide, usually involute, abaxial surfaces glabrous, adaxial surfaces glabrous or scabrous, margins strongly scabrous, blade of the second leaf below the panicles 8-56 cm long, 2-5(7) mm wide. Panicles 9-20 cm, not smoothly cylindrical, with 3-9 branches; branches 3-9 cm, appressed or spreading, with 20-50 spikelets. Spikelets 10-17 mm, lanceolate to ovate-lanceolate. Glumes glabrous or sparsely hispidulous, keels glabrous, hispid in whole or in part, or ciliate; lower glumes 4-9 mm, acuminate or awned; upper glumes 10-17 mm, exceeding the florets, keels hispid, lateral veins prominent, 1 on each side of the keel or 2-3 on 1 side of the keel, apices acuminate or awned; lemmas glabrous or sparsely hispidulous, apices obtuse, rounded, obscurely lobed, or apiculate; anthers 3-6 mm, poorly filled, indehiscent. 2n = 60, 60+2.
Maine, Md., N.J., Mass., N.B., N.S., P.E.I., Va., Conn., N.Y., Del., N.H., R.I.
Spartina ×caespitosa is found in disturbed areas of the drier portions of salt and brackish marshes, at some distance above the intertidal zone. It occurs sporadically along the coast from Maine to Maryland, a region where its putative parents, S. pectinata and S. patens, are sympatric. None of the populations Mobberley (1956) examined was growing in undisturbed land.
Mobberley's (1956) investigations led him to conclude that the populations of S. ×caespitosa are polythetic in origin. Part of the evidence for his conclusion was the variability he observed. It is this variability that makes it necessary to bring out the hybrid at several locations in the key. Its distribution is, however, very limited, a fact that may be more useful for identification than any of the morphological characteristics examined.