AN AMPHIDIPLOID OF × STIPORYZOPSIS

Abstract

THIS STUDY has resulted from the continued observations made upon some of the native and exotic grasses that are of economic importance in the northern Great Plains. Earlier studies resulted in the recognition of the sterile intergeneric hybrid XStiporyzopsis caduca (Beal) B. L. Johnson and Rogler (1943). More reCently, however, a single seedling was obtained by planting large numbers of what were assumed to be the empty florets from the sterile hybrid. This seedling developed into a highly fertile, true-breeding plant from which five generations of progenies have been grown in the breeding nurseries at the Northern Great Plains Field Station, Mandan, North Dakota. The history, the gross morphological features of the descendants and certain cytological and breeding characteristics of this amphidiploid are dealt with in this paper. An extensive bibliography has resulted from the reports concerning interspecific and intergeneric hybrids among the Gramineae. Myers (1947) has stated that over 200 instances of such hybridizations have been recorded. His tabulation included reports of presumed hybrids that had arisen spontaneously in nature, as well as those that had resulted from artificial crosses. Intergeneric hybridization involving Stipa yiridula Trin. and Oryzopsis hymenoides (Roem. and Schult.) Ricker was first suggested by Johnson and Rogler (1943) to explain certain taxonomically difficult specimens, as well as the sterile plants that had been taken from natural populations in the northern Great Plains and from the breeding nurseries at Mandan, North Dakota. Their conclusions were based upon the following facts: (1) the morphological characteristics of the presumed hybrids were intermediate between those of the species mentioned, and the hybrids were also both seed and pollen sterile; (2) the somatic chromosome number (2n = 65 ) was equal to the gametic complements of Stipa viridula (2n = 82) and Oryzopsis hymenoides (2n = 48); and (3) irregularity was observed during the meiotic divisions, this being particularly apparent at anaphase I and telophase I. The combination XStiporyzopsis caduca (Beal) B. L. Johnson and Rogler was established to recognize the parentage of the hybrid plants. The specific epithet was based upon Oryzopsis caduca Beal. Johnson (1945b) subsequently reported the recognition of additional hybrids of Oryzopsis hymenoides with the following Stipa species: S. thurberiana Piper, S. californica Merr. and Davy, S. scribneri Vasey, S. robusas (Vasey) Scribn., S. columbiana Macoun, and S. occidentalis Thurb. Stipa bloomeri Boland. was recognized as being of