Avena spp. - Bromus spp. Herbaceous Semi-Natural Alliance
Wild oats and annual brome grasslands

USDA Ecological Section Map

Summary Information

  • Primary Life FormHerb
  • Elevation0-2200 m
  • State RaritySNA
  • Global RarityGNA
  • DistributionUSA: CA, OR?; Mexico (NatureServe)
  • Endemic to CaliforniaNo
  • Invasive species rank See remarks
  • Endemic to California Floristic Province and DesertsNo
  • Date Added2016/12/01

Characteristic Species

Avena barbata, Avena fatua, Brachypodium distachyon, Briza maxima, Bromus diandrus, Bromus hordeaceus and/or Hordeum murinum is dominant or co-dominant with other non-natives in the herbaceous layer such as Atriplex semibaccata and Hordeum spp. Emergent trees and shrubs may be present at low cover.

Vegetation Layers

Herbs < 1.2 m; cover is open to continuous.

Membership Rules

  • Bromus diandrus > 60% relative cover with other non-natives in herbaceous layer and with a variety of annuals at low cover (Klein and Evens 2005).
  • Avena fatua > 50% relative cover, and native herbs relatively low in cover in the herbaceous layer (Keeler-Wolf and Evens 2006).
  • Avena spp. > 50% relative cover, and native herbs < 10% relative cover in the herbaceous layer (Evens and Kentner 2006, Klein et al. 2007).
  • Avena spp. > 75% relative cover; other non-native or native plants < 5% absolute cover, if present, in the herbaceous layer (Evens and San 2004).
  • Brachypodium distachyon > 60% relative cover in the herbaceous layer (Keeler-Wolf et al. 2003a).
  • Bromus diandrus, B. hordeaceus, and/or Brachypodium distachyon > 80% relative cover separately or co-dominant with non-natives; natives usually with low or insignificant cover (Klein et al. 2007).
  • Bromus hordeaceus > 50% relative cover in the herbaceous layer (Jimerson et al. 2000).
  • Avena, Brachypodium, Briza, Bromus diandrus, Bromus hordeaceus and/or Erodium > 50% relative cover individually or in combination (Klein et al. 2015).
  • Avena, Brachypodium, Briza, Bromus, Erodium and/or Hypochaeris > 30% relative cover individually, or share > 50% relative cover in the herbaceous layer (Buck-Diaz et al. 2021, Sikes et al. 2021).


All topographic settings in foothills, waste places, rangelands, openings in woodlands. The USFWS Wetland Inventory (2012 national list) recognizes Bromus hordeaceus as a FACU plant.

Other Habitat, Alliance and Community Groupings

MCV (1995) California annual grassland series
NVCS (2009) Avena fatua herbaceous alliance, Bromus (diandrus, hordeaceus, madritensis) herbaceous alliance
Calveg Annual grasses and forbs, Non-native/ornamental grass
Holland Valley and foothill grassland, Non-native grassland
Munz Valley grassland
WHR Annual grassland
CDFW CA Code 42.027.00

National Vegetation Classification Hierarchy

Formation Class Mesomorphic Shrub and Herb Vegetation (Shrubland and Grassland)
Formation Subclass Mediterranean Scrub and Grassland
Formation Mediterranean Grassland and Forb Meadow
Division California Grassland and Meadow
Macro Group California Annual and Perennial Grassland
Group Mediterranean California naturalized annual and perennial grassland