13.18  ΧLEYDEUM Barkworth

Mary E. Barkworth

Plants perennial; rhizomatous, sometimes shortly so. Culms to 140 cm tall, 1–3 mm thick. Spikes 10–15 cm long, 5–12 mm wide, excluding the awns, erect, sometimes lax, nodes with 2–3 spikelets; internodes 3–5 mm; disarticulation in the rachises, sometimes delayed. Spikelets appressed, with 1–3 florets. Glumes equal or unequal, 10–25 mm long, 0.2–1.5 mm wide, tapering from below midlength or subulate from the base; lemmas glabrous or hairy, awned, awns 2–10 mm; anthers 1.8–3 mm long, 0.1–0.3 mm thick. Caryopses not developed.

ΧLeydeum consists of hybrids between Hordeum and Leymus. The number of named ΧLeydeum hybrids is substantially lower than that for hybrids between Hordeum and Elymus; this probably reflects the lower likelihood of such hybrids being formed, because Leymus does not incorporate the H genome of Hordeum, whereas Elymus does. It is also possible that such hybrids are less likely to be recognized, because inland species of Leymus, like Hordeum, have narrow glumes. Of the three species recognized, two involve the coastal species Leymus mollis, which has flat glumes; these hybrids have intermediate glumes and rachises that tend to disarticulate. ΧLeydeum piperi, the only hybrid involving one of the inland species of Leymus, differs from Leymus in its disarticulating rachises, and from Hordeum in having 2 spikelets per node and 2–3 florets in the larger spikelets.

SELECTED REFERENCES Bowden, W.M. 1967. Taxonomy of intergeneric hybrids of the tribe Triticeae from North America. Canad. J. Bot. 45:711–724; Covas, G. 1949. Taxonomic observations on the North American species of Hordeum. Madroρo 9:233–264; Hodgson, H.J. and W.W. Mitchell. 1965. A new Elymordeum hybrid from Alaska. Canad. J. Bot 43: 1355–1358; Hultιn, E. 1968. Comments on the flora of Alaska and Yukon. Ark. Bot., n.s., 7:1–147.

1. ΧLeydeum piperi (Bowden) Barkworth

Plants shortly rhizomatous. Culms to 80 cm tall, about 1.5 mm thick. Leaves evenly distributed; sheaths smooth; auricles to 1.5 mm; ligules 0.5–0.8 mm, truncate to rounded; blades 10–20 cm long, 1.5–2.5 mm wide, tapering from near the base, abaxial surfaces scabridulous, adaxial surfaces scabrous, with about 12 usually more or less equally prominent veins, apices narrowly acute. Spikes 10–15 cm long, 10–15 mm wide including the awns, 5–7 mm wide excluding the awns, lax, nodes with 2(3) spikelets, 1 (central if 3) spikelet sessile, 1(2) spikelet(s) pedicellate, pedicels about 0.2 mm; internodes 3–5 mm, completely or mostly concealed by the spikelets; disarticulation tardy, in the rachises. Spikelets about 15 mm including the awns, about 10 mm excluding the awns, with 1–3 florets, the larger or central spikelets with 2–3 florets, the lateral or smaller spikelets with 1(2) floret(s). Glumes 10–15 mm long, about 0.2 mm wide, subulate, scabrous; lemmas glabrous, mostly smooth, scabrous distally, the largest lemmas of the larger spikelets 6–7 mm, with awns about 9 mm, the largest lemmas of the smaller or lateral spikelets about 5 mm, with awns about 5.5 mm; anthers 1.8–2.2 mm long, about 0.3 mm thick.

Covas (1949) and Bowden (1958) agreed that that the parents of ΧLeydeum piperi are Hordeum jubatum and Leymus triticoides. It is not known how common or widespread it is. It differs from ΧElyhordeum macounii in its subulate, rather than narrowly linear, glumes.

2. ΧLeydeum dutillyanum (Lepage) Barkworth

Plants cespitose, rhizomatous. Culms about 60 cm tall, 2–2.5 mm thick. Leaves evenly distributed on the culms; sheaths smooth, glabrous; auricles absent or to 0.3 mm; ligules 0.2–0.5 mm, truncate, entire; blades 20–30 cm long, 5.5–7 mm wide, glabrous, tapering from below midlength, abaxial surfaces with prominent midveins, all veins more or less equally prominent or a few less prominent, apices narrowly acute. Spikes about 15 cm long, about 25 mm wide including the awns, 10–12 mm wide excluding the awns, nodes with 2 spikelets; internodes 3–5 mm, concealed by the spikelets; disarticulation in the rachises. Spikelets 18–25 mm, with 2–3 florets, the distal floret reduced. Glumes unequal, subulate from the base, to 0.5 mm wide, hairy, hairs about 0.8 mm; lower glumes 13–17 mm; upper glumes 20–25 mm; lemmas 10–12 mm, strigose, hairs about 0.5 mm, awned, awns 8–10 mm; anthers 2–2.4 mm.

ΧLeydeum dutillyanum consists of hybrids between Hordeum jubatum and Leymus mollis (Bowden 1967). It has been reported only from Vieux-Comptoir, Quebec. It appears to disarticulate more readily than ΧL. littorale.

3. ΧLeydeum littorale (H.J. Hodgs. & W.W. Mitch.) Barkworth

Plants rhizomatous. Culms to 140 cm tall, about 3 mm thick. Leaves evenly distributed; sheaths smooth, glabrous; auricles 0.8–1 mm on the lower leaves; ligules 0.2–0.5 mm, truncate, entire; blades to 20 cm long, 6–9 mm wide, glabrous, tapering from near the base, abaxial surfaces smooth, with 20+ veins, veins more or less equally prominent or the primary veins slightly more prominent than the secondary veins, adaxial surfaces scabridulous, apices narrowly acute. Spikes 6.5–15 cm long, 12–15 mm wide including the awns, 8–12 mm wide excluding the awns, nodes with 2–3 spikelets; internodes 3.5–5 mm, concealed by the spikelets; disarticulation in the rachises, possibly also in the spikelets. Spikelets 12–15 mm, with 1–3 florets, the distal florets reduced. Glumes equal, 11–13 mm long, 0.8–1.5 mm wide, 3-veined at midlength, hairy, hairs about 0.5 mm, somewhat divergent, tapering from below midlength, apices awned, awns 3–4 mm long; lemmas 13–15 mm, hairy, awns 1–3 mm; anthers about 2.8 mm long, 0.1–0.3 mm thick.

ΧLeydeum littorale consists of hybrids between Hordeum brachyantherum and Leymus mollis. It has been collected in the Matanuska Valley, Alaska, and on the coast of Vancouver Island, British Columbia; it may be more widespread.