| # The grass genera of the world |

L. Watson, T.D. Macfarlane, and M.J. Dallwitz

### Thinopyrum A. Löve

~ Elytrigia, Elymus

Habit, vegetative morphology. Rigid, erect, glaucous perennial; rhizomatous. Culms 25–70 cm high; herbaceous; unbranched above. Young shoots extravaginal. The shoots aromatic. Leaves not basally aggregated; non-auriculate. Leaf blades linear; apically flat; narrow; 6–10 mm wide; rolled (involute); without cross venation; persistent. Ligule an unfringed membrane; truncate. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets; outbreeding, or inbreeding.

Inflorescence. Inflorescence a single spike (the spikelets usually appressed). Rachides flattened (on the side facing the spikelets, and smooth on the main angles). Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes disarticulating (fragile); disarticulating at the joints (the spikelets falling with the internode below). Spikelets solitary; not secund; distichous; sessile to subsessile; usually imbricate.

Female-fertile spikelets. Spikelets compressed laterally; falling with the glumes. Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension with incomplete florets. Hairy callus absent. Callus short (glabrous); pointed.

Glumes two; more or less equal (subequal); shorter than the spikelets; shorter than the adjacent lemmas; lateral to the rachis; pointed to not pointed (obtuse, acute or truncate); not subulate; awnless; non-carinate; similar. Lower glume 4–12 nerved. Upper glume 4–12 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped. Spikelets without proximal incomplete florets.

Female-fertile florets 2–10. Lemmas similar in texture to the glumes (leathery); entire; blunt; awnless; hairless; glabrous; non-carinate (except towards the tip); without a germination flap; 5 nerved; with the nerves confluent towards the tip. Palea present; relatively long; awnless, without apical setae; 2-nerved; 2-keeled. Lodicules present; 2; free; membranous; ciliate; ‘usually one-lobed’. Stamens 3. Anthers 4–12 mm long. Ovary apically hairy. Styles free to their bases. Stigmas 2; white.

Fruit, embryo and seedling. Fruit free from both lemma and palea; medium sized to large; longitudinally grooved; compressed dorsiventrally; with hairs confined to a terminal tuft. Hilum long-linear. Embryo small. Endosperm hard; without lipid.

Abaxial leaf blade epidermis. Costal/intercostal zonation lacking. Papillae absent. Long-cells similar in shape costally and intercostally (indistinguishable); of similar wall thickness costally and intercostally (fairly thick walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls (and pitted). Microhairs absent. Stomata absent or very rare; 29–39 microns long. Intercostal short-cells common; not paired (solitary). Costal short-cells neither distinctly grouped into long rows nor predominantly paired (solitary). Costal silica bodies absent, or poorly developed; tall-and-narrow (sometimes present).

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade. Leaf blade with distinct, prominent adaxial ribs; with the ribs very irregular in sizes (large, flat topped ribs alternating with small round topped ones). Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups (in the furrows). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with the primaries, in the large ribs); forming ‘figures’ (massive anchors with the main bundles). Sclerenchyma not all bundle-associated (there being a continuous abaxial layer, linking the ‘feet’ of the ‘anchors’). The ‘extra’ sclerenchyma in a continuous abaxial layer.

Cytology. Chromosome base number, x = 7. 2n = 14, 28, and 42. 2, 4, and 6 ploid. Haplomic genome content J. Haploid nuclear DNA content 5.5 pg (1 species).

Classification. Watson & Dallwitz (1994): Pooideae; Triticodae; Triticeae. Soreng et al. (2015): Pooideae; Triticodae; Triticeae; Triticinae. 5 species.

Distribution, phytogeography, ecology. Coasts of Europe.

Commonly adventive. Xerophytic; species of open habitats; halophytic. Coastal sands.

Hybrids. Intergeneric hybrids with Leymus and Elytrigia.

References, etc. Morphological/taxonomic: Löve 1984. Leaf anatomical: Metcalfe 1960; studied by us - T. junceiforme.

Illustrations. • General aspect (T. distichum): Gibbs Russell et al., 1990. • Thinopyrum distichum, abaxial epidermis of leaf blade: this project.

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, and classifications. See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., Macfarlane, T.D., and Dallwitz, M.J. 1992 onwards. The grass genera of the world: descriptions, illustrations, identification, and information retrieval; including synonyms, morphology, anatomy, physiology, phytochemistry, cytology, classification, pathogens, world and local distribution, and references. Version: 15th June 2025. delta-intkey.com’.

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