† Tall perennial meadow-grass. Awn bristle-like, almost as long as the nearly glabrous glume: spike long, cylindrical.
P. pratense, L.
†† Small, compact annual shore plant, with the glumes acute only and the keel ciliate above. Inflorescence not more than 1—1-1/4 inch long.
P. arenarium, L.
The rare P. Bœhmeri, Schrad. has the glumes merely tapering to a sharp point; and the rare P. alpinum, L. has a much shorter spike and glumes ciliate on the keels.
The rare P. asperum, Jacq. has broad, shortly mucronate glumes and a longer and more slender spike.
(2) Inflorescence a panicle—i.e. tufts or spreading stalked groups of spikelets are arranged on the main axis.
A. Inflorescence compact and irregular; a spike of tufts (spike-like panicle). Glumes four, the inner pair awned: paleæ minute. Stamens two only.
Anthoxanthum odoratum, L.
The four glumes and two stamens distinguish this grass at once. Other grasses with occasionally tuft-like inflorescences—e.g. species of Agrostis, Gastridium, Aira, Dactylis, Cynosurus, Poa, Triodia, Kœleria—are distinguished at once by having three stamens (Bromus occasionally has but two), only two glumes, several flowered spikelets, &c.