Notes on species delimination, species relationships and polyploidy in Avena L.

On the combined evidence from morphology, ecology, and cytogenetics, seven species are recognized in the genus Avena L. 1. A. claudaDur., 2. A. ventricosaBal. 3. A. longiglumisDur, 4. A. strigosaSchreb., 5. A. magnaMurphy et Terr., 6. A. murphyiLadiz. and 7. A. sativa L. The first three species are wild diploids. The fourth is a diploid-tetraploid complex of wild forms, weeds and cultivars. The fifth and sixth are wild tetraploids and the seventh constitutes a hexaploid aggregate of wild forms, weeds and cultivated forms. A short morphological and ecological characterization is given to each species. The cytogenetic, ecological and morphological evidence available on the evolutionary divergence and on the genetic affinities between the seven species is reviewed and discussed. The conclusion in drawn that in Avena there are two independent developments of polyploidy: 1. strigosa tetraploids, where the diploid background is well known; 2. the tetraploid-hexaploid of A. magna, A. murphyi and A. sativa (series Denticulatae). Here the first two species apparently represent the general tetraploid background from which hexaploid A. sativa evolved. It is also argued that it is impossible to explain the morphology, ecology and cytology of series Denticulatae in terms of the known diploid species of Avena, and a yet missing hypothetical diploid ancestor was extrapolated.