A taxonomic study of the annual Hordeum depressum and related species

To clarify the limits between H. depressum (Scribner & Smith) Rydberg and its close and remote allies, H. intercedens and H. pusillum, respectively, we carried out morphological and cytological examinations and various statistical analyses including classifactory discriminant analysis, canonical discriminant analysis, and logistic discrimination. We concluded that H. depressum, a tetraploid species, can usually be morphologically separated from H. intercedens, a diploid species with which it is most frequently confused, by the maximum width of the lateral lower glumes. Those of H. depressum are 0.1–0.5 mm wide, whereas those of H. intercedens are 0.4–1.3 mm wide. Very few specimens will fall in the area of overlap between the two species. In these cases morphological identification can be ascertained by the lodicules, which in H. depressum have an obvious and glabrous side lobe, whereas if there is a lobe in H. intercedens, it is rather small and beset with hairs at the margins. Populations of H. depressum are often large and occur in the intermontane region of northern and central California, whereas those of H. intercedens are typically small and occur along the coast of south California and Baja California. These two species are sympatric to a small degree, whereas H. pusillum does not occur in south and Baja California but is found throughout the United States and a few adjacent places in Canada. Other morphological and statistical findings are discussed.