This octoploid contains the St, Y, W, and H genomes (Zhang et al. 2009). The St genome is derived from Pseudoroegneria, the W genome from Australopyrum, and the H genome from Hordeum. The source of the Y genome is not known, there being no species known in which only the Y genome is present.
Perennial plants with solitary spikelets. Culm elongates and becomes prostrate after setting seed, growing to 2 m or more in length.
Plants perennial, stoloniferous. Culms 66-200 cm, internode below the inflorescence (peduncle) elongating greatly after anthesis and lying along the ground; lowest internode 0.5-1 mm thick
Leaf blades to 1.2-2 mm wide, flat to somewhat involute.
Inflorescence spikelike, 10-15 cm long, with 5-15 nodes; lowest internode with 18-28 mm long; middle internodes 12-20 mm long; rachis tough, prolonged beyond the base of the distal floret; disarticulation below the florets.
Spikelets solitary, tangential to the rachis, 25-40 mm long, with 6-8 florets.
Glumes lanceolate, 3-10 mm, coarsely scabrous, shorter than the adjacent lemmas, 3-veined, tapering into a stiff awn, awn to 5 mm long, scabrous.
Lemmas 6-10 mm long, mostly smooth and glabrous, midvein scabrous distally, awned, awns 15-35 mm long. Paleas 7-10 mm long, tapering to a narrow tip. Lodicules. Anthers 2-3 mm, yellow.
There is only one species. It is currently known as Elymus tenuis.
New Zealand, both islands
The only octoploid from New Zealand is currently treated as Elymus tenuis by all taxonomists.
Zhang, H.-Q., X. Bai, B.R. Lu, H.E. Connor, and Y.H. Zhou. 2009. Genome constitution of allooctoploid Elymus tenuis (Poaceae: Triticeae) from New Zealand. Abstracts, 6th International Triticeae Symposium. National Institute of Agrobiological Sciences (NIAS), Tsukuba, Ibarki, Japan.