Avena Linn., Sp. Pl. 1:79. 1753. Gen. Pl., ed. 5, 26. 1754; Malzew in Bull. Appl. Bot. Gen. Pl. Br., Suppl. 38. 1930; Bor, Fl. Assam 5:129. 1940; Sultan & Stewart, Grasses W. Pak. 2:280. 1959; Bor, Grasses Burma Ceyl. Ind. Pak. 432. 1960; Bor in Towns., Guest & Al-Rawi, Fl. Iraq 9:327. 1968; Bor in Rech.f., Fl. Iran. 70:322. 1970; Zohary in Davis et al., Plant life in South-west Asia, 235-263. 1971; Tzvelev, Poaceae URSS 236. 1976; Baum, Oats: Wild and Cultivated 1977; Rocha Afonso in Tutin et al., Fl. Fur. 5:206. 1980.
Annuals. Leaf-blades flat. Inflorescence an open or rarely contracted panicle with large pendulous spikelets. Spikelets 2-6-flowered (rarely more), the lower 1-3 florets bisexual, the others ± reduced, the terminal floret barren or vestigial; rhachilla disarticulating above the glumes and sometimes between the florets, or not at all in cultivated races; glumes lanceolate to ovate or elliptic, equal or almost so, rarely very unequal, rounded on the back, scarious-membranous or herbaceous-membranous, with thin margins, 7-11-nerved; lemmas lanceolate to ovate or oblong, shorter than or equalling the glumes, rarely exserted, rounded on the back, herbaceous, becoming hardened, 5-9-nerved, with a geniculate (or rarely straight) awn from the back, or awnless in some cultivated races; paleas shorter than the lemmas, 2-keeled; stamens 3; stigmas 2.
A genus of about 10-15 spontaneous species found as weeds of cultivation, and 10-12 cultivated races of which only two (Avena sativa Linn. and Avena byzantina C. Koch) are widely grown. Indigenous to the Mediterranean region, Northeast Africa and Central Asia; 4 species occur in Pakistan, 1 of them cultivated.
This is no more than an interim account of a very difficult and complex genus that is still far from being completely understood. The treatment is largely based on that of Malzew (1930), with some modifications following Tzvelev (1976). The most recent monograph of Oats (Baum 1977) has proven too difficult for the non-expert to use and is not designed for use in the field. Thus, some nomenclatural and taxonomic changes adopted by Baum have been ignored.
The mode of disarticulation of the rhachilla is an important character in Avena, particularly as to whether it breaks up between the lowest and second lemmas. If it does so, then the articulation can easily be seen as an oblique line from the side and as a bearded horseshoe-shaped join in face view. In non-disarticulating spikelets there is no such join and the rhachilla internodes are shorter and stouter.