This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol1", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Annual grasses with flat leaf-blades and spicate inflorescence, the spikes in pairs or digitate. Spikelets several-flowered, sessile, closely imbricated in two rows on one side of the rachis which is extended beyond them into a sharp point. Scales compressed, keeled, the 2 lower and the uppermost ones empty, the others subtending flowers. Stamens 3. Styles distinct, short. Stigmas plumose. Grain free, rugose, loosely enclosed in the scale. [Greek, referring to the digitately spreading spikes.]
A genus of a few species, natives of the warmer parts of the Old World. Type species: Cynosurus aegyptius L.
Culms 6'-2° long, usually decumbent and extensively creeping at the base. Sheaths loose, overlapping and often crowded, smooth and glabrous; ligule very short; blades 6' in length or less, 1"-3" wide, smooth or rough, sometimes pubescent, ciliate toward the base; spikes in pairs, or 3-5 and digitate, 1/2-2' long; spikelets 3-5-flowered; scales compressed, scabrous on the keel, the second awned, the flowering ones broader and pointed.
In waste places and cultivated ground, southern New York, Pennsylvania and Virginia to Illinois and California, south to Florida and Mexico. Widely distributed in tropical America. Naturalized from Asia or Africa. Crab-grass. Finger-comb-grass. July-Oct.