302 



MISC. PUBLICATION 200, U. S. DEPT. OF AGRICULTURE 



Cultivated oats fall into three 

 groups, according to the number of 

 chromosomes. Group 1, 7 chromo- 

 somes, A. brevis, A. strigosa. Group 2, 

 14 chromosomes, A. barbata. Group 3, 

 21 chromosomes, A. sativa, A. fatua 

 (including A. orientalis Schreb.), A. 

 nuda, A. sterilis, A. byzantina (includ- 

 ing A. sterilis var. algeriensis Trabut). 



Figure 408. — Avena barbata. Spikelets, X 1; tip of 

 lemma, X 5. (Davy 5023, Calif.) 



62. HELICTOTRICHON Besser 

 (Avena sec. Avenastrum Koch; included in Avena L. in Manual, ed. 1) 



Spikelets 3- to several-flowered, the rachilla bearded, disarticulating above 

 the glumes and between the florets; glumes about equal, 3- to 5-nerved, sub- 

 hyaline except toward the base; lemmas convex, the lower half subindurate 

 and several-nerved, the upper part subhyaline, awned from about the middle, 

 the awns twisted and geniculate, much exceeding the spikelets. Tufted peren- 

 nials with rather narrow panicles of shining spikelets. Type species, H. semper- 

 virens (Vill.) Pilger. Name from helictos, twisted, and "trichon," apparently 

 referring to the awn, which is twisted. Perennials, numerous in Eurasia, 1 

 introduced and 2 native in western North America. 



Blades involute; panicle 2 to 5 cm. long.. 3. H. mortonianum. 



Blades flat or folded; panicle 5 to 15 cm. long. 



Sheaths and blades glabrous 2. H. hookeri. 



Sheaths, at least the lower, and blades pubescent 1. H. pubescens. 



1. Helictotrichon pubescens 



(Huds.) Pilger. (Fig. 409.) Culms 

 erect, 50 to 80 cm. tall; sheaths pubes- 

 cent; blades flat, pubescent; panicle 

 narrow, open, 10 to 15 cm. long, the 

 flexuous branches ascending; spike- 

 lets mostly 3-flowered, 12 to 15 mm. 

 long, glumes and lemmas thin, shin- 

 ing, the rachilla with long white hairs ; 

 first glume 1- or 3-nerved, the second 

 3-nerved; lemmas about 1 cm. long; 

 awn attached about the middle, 1.5 to 

 2 cm. long. % — Waste places, 

 Connecticut and Vermont ; introduced 

 from Europe. 



2. Helictotrichon hookeri (Scribn.) 

 Henr. Spike oat. (Fig. 410.) Culms 

 densely tufted, 20 to 40 cm. tall; 

 blades firm, flat or folded, 1 to 3 mm. 

 wide, the margins somewhat thick- 

 ened; panicle long-exserted, narrow, 

 5 to 10 cm. long, the branches erect or 

 ascending, 1-flowered, or the lower 2- 



flowered; spikelets 3- to 6-flowered, 

 about 1.5 cm. long; glumes very thin, 

 slightly shorter than the spikelet; 

 lemmas firm, brown, scaberulous, 1 to 

 1.2 cm. long, the callus short-bearded, 

 the rachilla white-villous; awn 1 to 

 1.5 cm. long. % Dry slopes and 

 prairies, Manitoba to Alberta, Minne- 

 sota, Montana, and New Mexico. 



3. Helictotrichon mortonianum 

 (Scribn.) Henr. Alpine oat. (Fig. 

 411.) Culms densely tufted, 10 to 20 

 cm. tall; blades erect, firm, usually in- 

 volute; panicle short-exserted, pur- 

 plish, narrow, 2 to 5 cm. long, the 

 short branches erect, bearing usually 

 a single spikelet, 10 to 12 mm. long, 

 mostly 2-flowered; glumes exceeding 

 the florets; lemmas firm, glabrous, the 

 apex with 4 soft teeth, the callus with 

 a tuft of stiff hairs about 2 mm. long, 

 the rachilla long-villous ; awn 1 to 1.5 



