This is a large perennial grass with stems reaching 5 to 6 feet in length, flourishing in marshes and in the edges of ponds and tanks.
The stems are long, stout and spongy below, ascending from a creeping and rooting or floating root-stock; the lower internodes are often 1/2 inch or more in thickness, with nodes bearing in fascicles long stout roots clothed with fine lateral roots; and the upper internodes are long and slender.
The leaf-sheath is glabrous, striate. The ligule is a short broad membrane.
The leaf-blade is soft, flat, many-nerved, linear, finely acuminate, margins smooth, base rounded or subcordate, glabrous, 6 to 12 inches long, 1/4 to 1/2 inch broad.
The inflorescence is a strict spike-like panicle, 6 to 12 inches long by 1/4 to 1/3 inch broad, cylindric, interrupted below; the rachis terete, stout, channelled.
The spikelets are glabrous, green, herbaceous, densely packed in small fascicles, ovoid lanceolate, 1/6 to 1/5 inch long; many spikelets are imperfect.
Fig. 100.—Panicum interruptum.
1 and 2. Front and back view of a spikelet; 3. first glume; 4. second glume; 5. third glume; 6. palea of third glume; 7 and 8. the fourth glume and its palea; 9. ovary, lodicules and stamens.
There are four glumes. The first glume is hyaline, membranous, about 1/3 the length of the third glume, broadly ovate or orbicular, obtuse, 5-nerved. The second glume is membranous, ovate-oblong, obtuse, prominently 9-nerved. The third glume is as long as the second but broader, ovate-oblong, 9-nerved, paleate; palea is small with three stamens or without them. The fourth glume is shorter than the third glume, lanceolate, subacute, thinly coriaceous white, polished, dorsally convex; the palea is as long as the glume and thinly coriaceous. There are two small lodicules.