OregonFlora: Bromus tectorum vs. Poaceae

	Bromus tectorum	Poaceae
	cheatgrass, downy brome, downy chess	grass family
Habit	Plants annual, 5–90 cm tall.	Plants annual or perennial; cespitose, rhizomatous or stoloniferous.
Culms	puberulent.	usually herbaceous; erect to sprawling; internodes hollow or solid; nodes prominent and usually swollen.
Leaves	sheaths densely and softly retrorsely pubescent to pilose; upper sheaths sometimes glabrous; blades 1–16 cm × 1–6 mm, softly hairy on both surfaces.	alternate, 2-ranked; each consisting of a sheath that encircles the culm and a blade; sheaths open or closed with margins fused for much or all of their lengths; auricles present or absent; ligules usually present at the sheath-blade junction; on the side toward the culm, membranous or of hairs, rarely absent; blades usually linear to lanceolate with parallel veins.
Inflorescences	5–20 × 3–8 cm; open, nodding; branches 1–4 cm, drooping, 1-sided and longer than the spikelets, usually at least 1 branch with 4–8 spikelets.	usually complex aggregations of spikelets into panicles; racemes, or spikes, usually with a main axis; spikelets usually supported on pedicels; disarticulation above or below the glumes, usually beneath each floret, sometimes in or below the inflorescence axis.
Spikelets	10–20 mm, moderately laterally compressed, not densely crowded, 4–8 florets.	consisting of 2 glumes subtending 1–many florets arranged on either side of the rachilla, laterally or dorsiventrally compressed, occasionally round in cross section.
Glumes	villous, pubescent, or glabrous; lower glumes 4–9 mm, 1-veined; upper glumes 7–13 mm, 3–5-veined.	(0)2, with an odd number of veins, sometimes awned.
Stamens		(0)3(6).
Florets		usually bisexual, sometimes pistillate, staminate or sterile, usually consisting of a lemma and palea with the flower between them; the flower itself reduced to stamens; a pistil; and 2 lodicules.
Fruits		usually a caryopsis.
Lemmas	9–12 mm, lanceolate, glabrous or pubescent to pilose, 5–7-veined; tips acuminate; hyaline; bifid, with teeth 0.8–2(3)mm, awned; lemma awns 10–18 mm; straight.	usually with an odd number of veins, awned or awnless, with calluses; lemma awns; if present, arising at the tip; along the back or near the base, sometimes curved; bent, or twisted.
Anthers	0.5–1 mm.
Paleas		usually 2-keeled, often with additional veins.
2n	=14.

	Bromus tectorum	Poaceae
Distribution	[WildflowerSearch map] [BONAP county map]	[BONAP county map]
Discussion	Disturbed areas, sagebrush steppe, degraded grasslands, roadsides. 0–2400 m. BR, BW, Casc, Col, CR, ECas, Lava, Owy, Sisk, WV. CA, ID, NV, WA; throughout North America; worldwide. Exotic. Bromus tectorum is a relatively short grass with drooping inflorescences. Similar B. sterilis and B. diandrus have longer glumes, lemmas, and awns, and spikelets that hang down at a shallower angle than those of B. tectorum. The introduction of B. tectorum to shrub steppe habitats during a time of massive overgrazing in the late 1800s has made restoration of native plant communities difficult or impossible, even where grazing no longer occurs. Fast-growing B. tectorum seedlings outcompete slower growing native grass seedlings for water in drying soils. At maturity, the awns make B. tectorum unpalatable to livestock.	Cosmopolitan. Approximately 700 genera; 99 genera treated in Flora. With approximately 11,000 species, Poaceae is the fourth largest plant family in the world and the most economically and ecologically important. Grasses grow in most terrestrial habitats and are dominant or co-dominant in grasslands and savannas. The world’s major grain crops are grasses, including corn, rice, wheat, barley, sorghum, millet, oats, and rye. Some grass species are serious weeds, threatening natural ecosystems, harming livestock, and competing with cultivated crops. Arundo donax, giant reed, has spread very locally from ornamental plantings in Jackson County. Plants are strongly rhizomatous; culms (2)3–10m tall, 2+cm wide near the base; leaves 30–100 × 2–7(9)cm; inflorescence a fluffy panicle; lemmas 8–12 mm with hairs 4–9 mm. Efforts are being made to eradicate this population. It is an invasive weed in California. The following identification hints may be helpful when keying within this family: If the inflorescence is a dense spike, break the inflorescence axis to isolate a node and count the spikelets attached there. Spikelet and lemma measurements exclude the awns. To determine spikelet compression, break off a single spikelet and lay it down. If both glumes are visible at the same time, it is laterally compressed. If only one glume is visible, it is dorsiventrally compressed.
Source	Flora of Oregon, volume 1, page 374 Barbara Wilson, Richard Brainerd, Nick Otting	Flora of Oregon, volume 1, page 331
Sibling taxa	B. arenarius, B. briziformis, B. catharticus, B. ciliatus, B. commutatus, B. diandrus, B. hordeaceus, B. inermis, B. japonicus, B. laevipes, B. madritensis, B. orcuttianus, B. pacificus, B. rubens, B. secalinus, B. sitchensis, B. squarrosus, B. sterilis, B. suksdorfii, B. vulgaris
Synonyms	Bromus tectorum var. glabratus, Bromus tectorum var. nudus, Bromus tectorum var. tectorum
Web links	Local floras: BC, CA, OR, WA Local Web sites: CalFlora, CalPhotos, Flora NW, PNW Herbaria WildflowerSearch iNaturalist (observations) USDA Plants Database LBJ Wildflower Center SEINet Plants of the World Online Encyclopedia of Life Wikipedia Google Image Search	Local floras: OR Local Web sites: Flora NW, PNW Herbaria WildflowerSearch iNaturalist (observations) LBJ Wildflower Center SEINet Plants of the World Online Encyclopedia of Life Wikipedia Google Image Search

Poaceae

cheatgrass, downy brome, downy chess

grass family

Habit

Plants annual, 5–90 cm tall.

Plants annual or perennial; cespitose, rhizomatous or stoloniferous.

Culms

puberulent.

usually herbaceous; erect to sprawling;

internodes hollow or solid;

nodes prominent and usually swollen.

Leaves

sheaths densely and softly retrorsely pubescent to pilose; upper sheaths sometimes glabrous;

blades 1–16 cm × 1–6 mm, softly hairy on both surfaces.

alternate, 2-ranked; each consisting of a sheath that encircles the culm and a blade;

sheaths open or closed with margins fused for much or all of their lengths;

auricles present or absent;

ligules usually present at the sheath-blade junction; on the side toward the culm, membranous or of hairs, rarely absent;

blades usually linear to lanceolate with parallel veins.

Inflorescences

5–20 × 3–8 cm; open, nodding;

branches 1–4 cm, drooping, 1-sided and longer than the spikelets, usually at least 1 branch with 4–8 spikelets.

usually complex aggregations of spikelets into panicles; racemes, or spikes, usually with a main axis;

spikelets usually supported on pedicels;

disarticulation above or below the glumes, usually beneath each floret, sometimes in or below the inflorescence axis.

Spikelets

10–20 mm, moderately laterally compressed, not densely crowded, 4–8 florets.

consisting of 2 glumes subtending 1–many florets arranged on either side of the rachilla, laterally or dorsiventrally compressed, occasionally round in cross section.

Glumes

villous, pubescent, or glabrous;

lower glumes 4–9 mm, 1-veined;

upper glumes 7–13 mm, 3–5-veined.

(0)2, with an odd number of veins, sometimes awned.

Stamens

(0)3(6).

Florets

usually bisexual, sometimes pistillate, staminate or sterile, usually consisting of a lemma and palea with the flower between them; the flower itself reduced to stamens; a pistil; and 2 lodicules.

Fruits

usually a caryopsis.

Lemmas

9–12 mm, lanceolate, glabrous or pubescent to pilose, 5–7-veined;

tips acuminate; hyaline; bifid, with teeth 0.8–2(3)mm, awned;

lemma awns 10–18 mm; straight.

usually with an odd number of veins, awned or awnless, with calluses;

lemma awns; if present, arising at the tip; along the back or near the base, sometimes curved; bent, or twisted.

Anthers

0.5–1 mm.

Paleas

usually 2-keeled, often with additional veins.

=14.

Poaceae

Distribution

[WildflowerSearch map]

[BONAP county map]

Discussion

Disturbed areas, sagebrush steppe, degraded grasslands, roadsides. 0–2400 m. BR, BW, Casc, Col, CR, ECas, Lava, Owy, Sisk, WV. CA, ID, NV, WA; throughout North America; worldwide. Exotic.

Bromus tectorum is a relatively short grass with drooping inflorescences. Similar B. sterilis and B. diandrus have longer glumes, lemmas, and awns, and spikelets that hang down at a shallower angle than those of B. tectorum. The introduction of B. tectorum to shrub steppe habitats during a time of massive overgrazing in the late 1800s has made restoration of native plant communities difficult or impossible, even where grazing no longer occurs. Fast-growing B. tectorum seedlings outcompete slower growing native grass seedlings for water in drying soils. At maturity, the awns make B. tectorum unpalatable to livestock.

Cosmopolitan. Approximately 700 genera; 99 genera treated in Flora.

With approximately 11,000 species, Poaceae is the fourth largest plant family in the world and the most economically and ecologically important. Grasses grow in most terrestrial habitats and are dominant or co-dominant in grasslands and savannas. The world’s major grain crops are grasses, including corn, rice, wheat, barley, sorghum, millet, oats, and rye. Some grass species are serious weeds, threatening natural ecosystems, harming livestock, and competing with cultivated crops. Arundo donax, giant reed, has spread very locally from ornamental plantings in Jackson County. Plants are strongly rhizomatous; culms (2)3–10m tall, 2+cm wide near the base; leaves 30–100 × 2–7(9)cm; inflorescence a fluffy panicle; lemmas 8–12 mm with hairs 4–9 mm. Efforts are being made to eradicate this population. It is an invasive weed in California. The following identification hints may be helpful when keying within this family: If the inflorescence is a dense spike, break the inflorescence axis to isolate a node and count the spikelets attached there. Spikelet and lemma measurements exclude the awns. To determine spikelet compression, break off a single spikelet and lay it down. If both glumes are visible at the same time, it is laterally compressed. If only one glume is visible, it is dorsiventrally compressed.

Source

Flora of Oregon, volume 1, page 374
Barbara Wilson, Richard Brainerd, Nick Otting

Flora of Oregon, volume 1, page 331

Sibling taxa