Avena barbata largely reproduces by selfing in natural populations, with very low rates of outcrossing.

As an introduced species it also occurs in other Mediterranean-like habitats of New Zealand, Australia, South Africa, Argentina, Chile, Brazil, and Uruguay.

[5] Genetic evidence indicates that A. barbata in Argentina and California originated from Spain, during the Spanish colonization of the Americas.

[6] Californian populations of Avena barbata represent one of the most extensively studied examples of putative "ecotypes" in the plant literature.

[22][23] The general pattern that emerged from these earlier studies was that throughout the Central Valley of California, consisting of semiarid grasslands and oak savannahs, and extending south to San Diego, populations of this species were dominated by a monomorphic phenotype possessing dark/black seeds with hairy lemmas, as well as smooth leaf sheaths; these morphological characters were correlated with a specific isozyme pattern as well as a specific ribosomal DNA genotype.

Populations outside the Central Valley, along the coastal strip, the intermontane regions of the coast ranges, and the higher foothills of the Sierra Nevada mountains, were either monomorphic for white seeds with generally smooth lemmas and hairy leaf sheaths or were polymorphic with varying mixtures of the seed and leaf sheath characters.

The mesic type has never apparently been observed south of approximately the same latitude as Monterey, either in coastal ranges, the Central Valley, or the foothills of the Sierras.

When the morphological traits as well as the allozyme and ribosomal DNA genotypes were considered together, it is argued that there are six ecotypes in the otherwise "mesic" classification.

Davis, Pèrez de la Vega and Pedro Garcia of the University of Leon, and E. Nevo in Israel ([27][28][29]).