Plants perennial; cespitose, shortly rhizomatous. Culms 30-90 cm, erect or decumbent,
forming distinct clumps; nodes 2-3,
glabrous or puberulent; internodes glabrous
or puberulent. Sheaths glabrous or with
hairs; auricles to 1 mm on the lower
leaves; ligules 0.4-1.0 mm, glabrous
or ciliate, truncate, erose; blades
10-20 cm long, 2-3 mm wide, scabridulous, glabrous or sparsely pilose, margins
sometimes ciliate. Panicles 8-20 cm
long, lax; branches scabridulous,
with 1-2 spikelets. Spikelets 20-32
mm, lanceolate, becoming cuneate, with 5-8 florets. Glumes glabrous, sometimes scabridulous on the veins; lower glumes 6.5-10 mm, 1(3)-veined; upper glumes 7.5-12 mm, 3-5-veined; lemmas 10-13 mm, oblong to lanceolate,
rounded over the midvein, 7-veined, glabrous or appressed-hairy, sometimes
scabridulous, apices acute, entire or minutely bifid; awns 4-8 mm, straight or slightly spreading, arising less than 1.5
mm below the lemma apices; anthers 2.5-5.2
mm. 2n = 70.
Bromus riparius is an Asian species that was introduced to the
United States in the late 1950s for cultivation as a pasture grass. Various
cultivars are now grown, mainly in Canada and the northwestern United States. The
description given here is derived in part from cultivated specimens. North
American plants have sometimes been referred to incorrectly as Bromus biebersteinii Roem. & Schult.-(Vogel et al. 1996). Bromus riparius differs from that species in having acute lemma
apices and, usually, more pubscent leaf blades, sheaths, and lemmas.
The existence of Bromus riparius in the Flora region was not realized until
shortly before this treatment was submitted for publication, making it impossible
to fully investigate its similarities to B.
inermis-and B.
pumpellianus,
particularly subsp. dicksonii. It appears to differ from both
species in having shorter culms on average, longer awns than B. inermis, and shorter rhizomes than B. pumpellianus subsp. pumpellianus.
