36. Bouteloua Lag. (grama grass)
Plants perennial (annual elsewhere), with or without rhizomes.
Flowering stems glabrous or minutely hairy at the nodes. Leaf sheaths rounded
on the back, glabrous or hairy, the ligule a line or band of hairs. Leaf blades
flat or with the margins inrolled. Inflorescences with 1–70 spikes, these
arranged pinnately, all appearing lateral and spreading or angled downward.
Spikes 0.8–4.0 cm long, with 2 to numerous spikelets, these loosely ascending
(angled) in 2 rows along 1 side of the flattened axis, disarticulating above
the glumes (leaving the axis of the spike appearing chaffy or scaly after the
florets have been shed) or each of the spikes shed intact as a unit (leaving
the unbranched, main axis of the inflorescence after the spikes have been
shed). Spikelets with 1 perfect floret below usually 1 or 2 reduced, sterile
florets. Glumes unequal in size and shape, the lower glume narrower and shorter
than the upper glume, both 1‑nerved and sharply pointed at the tip, but
usually unawned. Lemmas of fertile florets 3‑nerved, the tip with 3
teeth, the middle tooth usually short‑awned. Lemmas of sterile florets
smaller than those of the fertile florets, but the awns usually longer,
sometimes the floret reduced to a 3‑awned structure. Paleas of fertile
florets 2‑keeled (absent in sterile florets). Fruits narrowly oblong‑elliptic.
About 40 species, North America to South America, Caribbean Islands.
The species of Bouteloua fall into two very well
separated subgenera. Bouteloua curtipendula belongs to the subgenus Bouteloua,
which is characterized by inflorescences with relatively numerous spikes that
are shed intact as individual units and 1–16 spikelets per spike. Bouteloua
gracilis and B. hirsuta belong to the subgenus Chondrosum
(Desv.) Gould, which differs in having inflorescences with relatively few
spikes that are persistent on the main axis, with the mostly 20–60 spikelets
per spike disarticulating above the glumes. Several members of subgenus Chondrosum
are important components of shortgrass prairie and other arid grassland
communities in the western United States. These two groups are treated as
distinct genera by some authors (Clayton, 1982; Clayton and Renvoize, 1986;
Pohl, 1994), but the presence of a few species with somewhat intermediate
morphology has slowed the acceptance of this interpretation.
The cytological situation in Bouteloua is complicated
by polyploidy and aneuploidy, and a long series of chromosome counts has been
reported for most species. In the treatment below, the range of counts for each
taxon is listed, along with the most commonly reported number(s).