The systematics of Avena sterilis and A. fatua (Gramineae). A critical study.
The hexaploid morphospecies A. sterilis and A. fatua, the wild and the weed oats, and the cultivated crop A. sativa, are commonly regarded as the principal components of a tripartite classification system. It is superior to the two alternatives: (1) to follow a closer biospecies concept in recognizing only a single species, A. sativa, or (2) to subdivide both A. sterilis and A. fatua in three "semispecies", primarily on the basis of micromorphological characters. Consequently, the well-known Avena system is modified here and updated, omitting the cultivars from any taxonomic consideration; the following subspecies are recognized: A. sterilis subsp. sterilis, A. sterilis subsp. atherantha, A. sterilis subsp. ludoviciana, A. fatua subsp. fatua, A. fatua subsp. septentrionalis, A. fatua subsp. meridionalis, A. fatua subsp. aemulans; the combinations A. sterilis subsp. atherantha and A. fatua subsp. aemulans are new. An important macromorphological criterion, useful for scientific and practical purposes, is the abscission scar configuration of the lemmas. The A. sativa fatuoids and steriloids cannot be distinguished clearly from the A. fatua taxa; therefore, they are united together with A. fatua in a single taxonomic group under this name. This procedure is in agreement with the widely accepted hypothesis of the origin of A. fatua in historical times from the cultivated A. sativa, the latter being derived from A. sterilis (monophyletic hypothesis vs. diphyletic hypothesis with A. sterilis and A. fatua as ancestors). A comprehensive identification key for all subspecies is included.