A. agrestis, L. in S. England has shorter leaves, and ridges not flattened; it is a troublesome pest of arable land, but does not usually invade pasture.
A. geniculatus, L. is semi-aquatic, and like the last. It is easily recognised by its sharply bent “knees," and is of little value (Fig. [3]).
Alopecurus shows resemblances to Lolium (see p. [49]), Festuca (see p. [50]), and Agrostis (see p. [52]). If well grown its ridged sheath and leaves, the former brown or black at the base, aid in distinguishing it.
(2) Blades either devoid of ridges or with very inconspicuous ones.
✲ No trace of ridges, and the mid-ribs not prominent, but the leaves show median lines flanked by finer ones when held up. Blades thin and narrow. Somewhat keeled.
(i) Shoots compressed.
Poa compressa, L. (Flat-stemmed Meadow-grass). Leaves rather short, more or less glabrous or glaucous, and V-shaped at the base; shoots compressed, and naviculate in section. Ligule short and thin. Sheath tends to be closed below. A creeping perennial on commons and waste lands, and of little or no value.
Poa annua, L. (Annual Meadow-grass). Small annual. Compressed shoots, limp. Leaves linear, pale, sub-acute, thin, often wavy, flat, flaccid, bright green; dull or slightly shining and V-shaped in section below. Ligule long, pointed, whitish and clasping the shoot. It is a harmless weed, and since it puts out shoots all the year round, furnishes a certain amount of pasturage.
(ii) Shoots terete or nearly so.
Poa nemoralis, L. (Wood Poa). Leaves and sheaths smooth. Blade bright green, thin, often glaucous, linear-narrow, flaccid, acute. Ligule almost obsolete. Section of shoots round. Of little value.
Poa bulbosa, L. (Bulbous Meadow-grass). Stems bulbous at the base. Ligule long and acute. Leaves very narrow and tapering. Sections of shoot round. Coasts of S. and E.
All the Poas, except the aquatic ones (Glyceria) and P. maritima, have glabrous ribless blades with the median lines, and slight keel.
P. pratensis, P. alpina and P. trivialis (Fig. [8]) have entire sheaths (as have Glyceria fluitans, G. aquatica and P. maritima), but the others have them split some way down.
The leaves of P. pratensis and P. compressa are firmer than the thin leaves of P. annua, P. trivialis and P. nemoralis.
Sheaths flattened in P. pratensis, P. compressa, P. annua, and P. trivialis; but rounded in P. nemoralis. Glyceria aquatica and G. fluitans have netted sheaths.
Poa annua is annual, and P. bulbosa has the bulbous base. P. maritima has involute leaves and no keel, and the rare P. alpina has short rigid keeled mucronate leaves, with tip often inflexed and thickened scabrid edges.
The leaves of Avena are apt to appear similar to those of the Poas at first sight, but the former are hairy, and ridged, dry as well as thin, and the peculiar median lines of Poa are wanting. Poa bulbosa has drier leaves than usual, but its leaves are devoid of ridges.
✲✲ Ridges can be detected, but are slight and not distinct. Margins scabrid, at least at the base.
† Leaves firm, flat, linear, acuminate, not narrowed below. Glabrous. Ligule membranous.
Digraphis arundinacea, Trin. (Reed-grass). Sheathed leaves round in section; blades convolute, tapering above, flat, firm, long and broad (1 in.) below. Mid-rib and veins numerous, and prominent below. Stoloniferous: branches extra-vaginal, often with deep red basal scales. Sheaths with much overlapping membranous margins, with a collar-like ledge above. Ligule long and somewhat acute. Wet ditches, &c., of no value (Figs. [7], [14]).
For distinction between Digraphis and Dactylis see p. [41]. Poa pratensis is at once distinguished by its flattened shoots, more rounded leaf apex and shorter ligule. Arundo Phragmites is easily distinguished by the ligule (see p. [51]), and the other aquatic grasses are quite different (see p. [39]).