Natural and Artificial × Elymordeum Hybrids

× Elymordeum Lepage is a validly published name for hybrids of Elymus L. × Hordeum L.; × Hordelymus should not be used as a name for these hybrids. Eight × Elymordeum hybrids are listed in this paper: × Elymordeum dutillyanum Lepage (Elymus mollis subsp. mollis × Hordeum jubatum); × Elymordeumschaackianum hybr. nov. (Elymus hirsutus × Hordeum brachyantherum); × Elymordeumpiperi hybr. nov. (Hordeum jubatum × Elymus triticoides); × Elymordeumdakotense hybr. nov. (Hordeum jubatum × Elymus canadensis); !× Elymordeumtriploideum hybr. nov. (2n = 21) (Hordeum distichon × Elymus racemosus var. racemosus); !× Elymordeumstebbinsianum hybr. nov. (Hordeum brachyantherum × Elymus glaucus); !× Elymordeumberkeleyanum hybr. nov. (Hordeum brachyantherum × Elymus condensatus); and !× Elymordeummontanense (Scribn. in Beal) comb. nov. (Elymus virginicus × Hordeum jubatum). Most specimens of !× Elymordeum montanense are nm. montanense; two specimens with pubescent lemma backs are nm. pubescens nm. nov. The parentages of the four hybrids designated by !× have been experimentally confirmed.Most of the parental species of Elymus and Hordeum were tetraploid (2n = 28); the exception was the diploid, (2n = 14), Hordeum distichon. One artificial hybrid, !× E. triploideum, was from Russia; the other hybrids were natural or artificial hybrids from North America. Seven of the parental species of Elymus and Hordeum are native in North America; two occur in Northeastern Asia and North America, one is native in Central Asia and one parent is a cultivated barley. In natural and artificial F1× Elymordeum hybrids, the anthers did not dehisce, the pollen was completely bad, and the spikes never set seed.The natural hybrids of !× Elymordeum montanense occur rarely and sporadically from Montana to Nova Scotia. An artificial F1hybrid was produced in 1954–55 from the cross, Elymus virginicus L. f. virginicus × Hordeum jubatum L. var. jubatum. The artificial hybrid was identical with the natural hybrid from Lower Onslow, Nova Scotia. The hybrids and parental plants were tetraploid, 2n = 28, and there were many meiotic irregularities in the pollen mother cells.