Avena fatua, L.
Palea parchment-like, lanceolate-terete, acuminate and bifid at the apex, rounded on the back and with yellow hairs on the lower part. 15 × 3 mm. Awn brown, twisted and bent, arising from the middle, about 30 mm. long. Caryopsis 7 mm. long, hairy at the top and distinctly grooved. Rachilla with fine bristles.
Avena pratensis, L.
Palea very similar to A. fatua, apex 2-4-toothed or bifid, rachilla with stiffer hairs. Caryopsis about 5 mm. long.
Avena pubescens, Huds. is a variety of A. pratensis found on dry calcareous soils. The caryopsis is very narrow, and the rachilla long and feathered with hairs. "Seed" shorter than A. pratensis, 10-13 mm., and darker in colour.
A. fatua is an excellent type of the grasses with dorsal twisted and bent awns, and easily examined on account of its size. The student will find difficulties with other species of Avena and Arrhenatherum.
Harz says the stiff hairs of Avena bring about the formation of intestinal concretions (phytobezoars) and are therefore dangerous to domestic animals.
✲✲ Palea not more than 7-10 mm. long.
† Caryopsis 4-5 mm. long.
Arrhenatherum avenaceum, Beauv. (Fig. [47]).
Paleæ papery, ribbed. Awn 13-15 mm., twisted below; paleæ, with a tuft of hairs below and a ciliate keel, investing the fruit: the whole being cylindrical, 8-10 mm. × 1·5.
Caryopsis 4-5 mm. × 1·2, fusiform, pubescent. Rachilla hairy.
The distinctive difference between Avena and Arrhenatherum is in the spikelets as a whole. The latter has the lower flower of each spikelet male only. Samples contain the “double seeds,” and the awn of the upper fertile portion is short (see Fig. [69]).
†† Caryopsis not more than 3 mm. long. A tuft of hairs on rachilla and base.