Elyhordeum Iowense, a New Intergeneric Hybrid in the Triticeae

Abstract

The "generic" name X Elyhordeum is used for hybrids between various species of Elymus and Hordeum. It has recently been reviewed by Bowden (Canad. J. Bot. 36: 101-123. 1958) who listed eight hybrids. The plants discussed below conform to the generic description of X Elyhordeum. They have the general aspect of Hordeum jubatum L., with which they grow. A specimen was brought in for identification by Mr. Charles Crane, a student in Ames High School, who found the stand. In their fragile rachis, spikelet triads, and slender awns, the plants are similar to Hordeum jubatum, but are sterile. They occur along the grassy road ditch of a, gravelled county road, adjacent to a cornfield in the vicinity of Ames. These apparent hybrids were first seen by me in September, 1964, and have been observed repeatedly since. At least 75 of the plants have been counted along 300 m of the roadside. They occur in the road ditch, in dense turf with such species as Poa pratensis L., Spartina pectinata Link, and Calamagrostis canadensis (MVlichx.) Beauv. Scattered plants of Elymus canadensis L. and a few dicotyledonous herbs are also present. This roadside, like all others in the county, has been repeatedly sprayed with herbicides over a period of years, and the vegetation consisted primarily of grasses. At each point where clumps of the hybrids were observed, Elymus villosus Muhl. ex Willd. and Hordeum jubatum also grew. No trees were present in the immediate vicinity, and from the soil type and topography, it is possible to determine that the original vegetation was prarie. The occurrence of Elymus villosus in such an open habitat is unusual, since this is largely a woodland species. These hybrids are completely sterile and can spread only by the gradual stooling of the clumps. Since the plants are distributed over about 300 m of roadside and occur on both sides of a gravelled road, it is very unlikely that they are the products of a single isolated hybridization, propagated by vegetative spread. In observing the habitat, I found hybrids only immediately adjacent to both parents. Clumps of all sizes and apparent ages can be found, from those consisting of only one or two. culms to vigorous individuals as much as 20 cm across at the base and with many inflorescences. It seems evident, therefore, that this cross occurs readily and repeatedly at this site and that the hybrids establish adjacent to the parents. This. particular hybridization has not been reported before, and we have no indication from Iowa herbarium specimens that it occurs elsewhere in the state. Since theparents cross so freely at this location, the genetic barriers between these parental species must be weak. However, the habitats occupied by Hordeum jubatum and Elymus villosus are very different, and these species may not ordinarily cross because of their ecological differences. Hordeum jubatum usually occupies disturbed roadsides and overgrazed pastures, whereas E. villosus is almost universally foundc