Bromus sect. Ceratochloa
Plants annual, biennial, or perennial. Spikelets elliptic to lanceolate, strongly laterally compressed, with 3-12 florets. Lower glumes 3-7(9)-veined; upper glumes 5-9(11)-veined; lemmas lanceolate, laterally compressed, strongly keeled, at least distally, apices entire or with acute teeth, teeth shorter than 1 mm; awns straight, erect to slightly divaricate.
Bromus sect. Ceratochloa is native to North and South America, and contains about 25 species. It is marked by polyploid complexes; the major one in North America is the Bromus carinatus complex. This treatment recognizes six species in the complex: B. aleutensis, B. arizonicus, B. carinatus, B. maritimus, B. polyanthus, and B. sitchensis. The lowest chromosome number known for members of this complex is 2n= 28, found in B. carinatus; the highest is 2n = 84, found in B. arizonicus. The remaining species are hexaploids with 2n = 42, or octoploids with 2n = 56. One other species in the section, B. catharticus, has been introduced from South America and is also part of a polyploid complex.
There is morphological intergradation among the species recognized here, and some evidence that these intermediates are sometimes partially fertile (Harlan 1945a, 1945b; Stebbins and Tobgy 1944; Stebbins 1947). Stebbins and Tobgy (1944) commented that partial hybrid sterility between plants placed in different species on the basis of their morphology "supports the recognition of more than one species among the octoploid members of the complex," but later Stebbins (1981) stated that "... all the North American octoploids. . . should be united into a single species, in spite of the barriers of hybrid sterility that separate them."
|1||Lemmas unawned or with awns to 3.5 mm long; lemmas usually glabrous, sometimes pubescent distally, veins prominent for most of their length||Bromus catharticus|
|1||Lemmas awned, awns (2)4-17 mm long; lemmas pubescent or glabrous, veins obscure or prominent.||> 2|
|2||Lower panicle branches shorter than 20 cm, with 1-3 spikelets on the distal 1/2, sometimes confined to the tips; culms 3-7 mm thick.||> 3|
|3||Lower panicle branches shorter than 20 cm, spreading to drooping||Bromus sitchensis|
|3||Lower panicle branches shorter than 10 cm, stiffly ascending||Bromus aleutensis|
|2||Lower panicle branches usually shorter than 10 cm, with 1-5 spikelets variously distributed; culms less than 4 mm thick.||> 4|
|4||Upper glume about as long as the lowest lemma in each spikelet; lemmas glabrous or pubescent distally or throughout, the marginal hairs, if present, longer than those elsewhere||Bromus arizonicus|
|4||Upper glume shorter than the lowest lemma in each spikelet; lemmas glabrous or pubescent only on the margins or throughout, if throughout, the marginal hairs similar in length to those elsewhere.||> 5|
|5||Panicles dense; spikelets crowded, overlapping, usually longer than the pedicels and branches; culms 20-70 cm tall, sometimes geniculate at the base; blades glabrous; ligules 1-6 mm long||Bromus maritimus|
|5||Panicles loose to compact; spikelets not crowded or overlapping, shorter than at least some pedicels and branches; culms 30-120(180) cm tall, erect or decumbent; blades glabrous or hairy; ligules 1-4 mm long.||> 6|
|6||Lemmas and sheath throats glabrous||Bromus polyanthus|
|6||Lemmas and/or sheath throats with hairs.||> 7|
|7||Lemmas 9-13-veined, veins often raised and riblike distally or throughout||Bromus catharticus|
|7||Lemmas 7-9-veined, veins usually not raised or riblike||Bromus carinatus|