The grass genera of the world

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

Pascopyrum A. Löve

~ ‘Agropyron smithii’, Elymus, Elytrigia

Habit, vegetative morphology. Strongly glaucous perennial; rhizomatous. Culms 30–90 cm high; herbaceous; unbranched above. Leaves not basally aggregated; auriculate (slender, pointed, on some of the sheaths). Sheath margins free. Leaf blades narrow; 2–7 mm wide; flat, or rolled (stiff, involute when dry); not pseudopetiolate; without cross venation; persistent. Ligule an unfringed membrane; truncate; 1 mm long.

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

Inflorescence. Inflorescence a single spike, or a false spike, with spikelets on contracted axes (erect, 7–15 cm long, the ‘clusters’ reduced to one or two spikelets per node); espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary (at all nodes), or solitary and paired (with a few pairs at the middle nodes); not secund; distichous; sessile; imbricate (not pectinate).

Female-fertile spikelets. Spikelets mostly 15–25 mm long; compressed laterally; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension with incomplete florets.

Glumes two; more or less equal (to slightly unequal); shorter than the spikelets; long relative to the adjacent lemmas (the G2 generally equalling or exceeding the L1); lateral to the rachis; hairless; glabrous; pointed (tapering); not subulate (lanceolate and tapering, by contrast with those of Leymus -but subulate when dry); awned, or awnless (tapering into an acute or short-awned apex); non-carinate; similar (rigid, with scarious margins). Lower glume 3–7 nerved. Upper glume 3–7 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped.

Female-fertile florets 4–9. Lemmas similar in texture to the glumes (firm, pale); not becoming indurated; entire; pointed, or blunt; awnless, or mucronate, or awned. Awns when present, 1; median; apical; non-geniculate; much shorter than the body of the lemma; entered by several veins. Lemmas glabrous, or basally pubescent; non-carinate; without a germination flap; ‘obscurely nerved’; with the nerves confluent towards the tip. Palea present; relatively long; 2-nerved; 2-keeled. Palea back hairy (pubescent). Stamens 3. Anthers 4–6 mm long. Styles free to their bases. Stigmas 2; white.

Abaxial leaf blade epidermis. Costal/intercostal zonation fairly conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally (fairly thick walled, pitted). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs absent. Stomata common; (72–)75–81(–84) microns long. Subsidiaries low dome-shaped, or parallel-sided. Guard-cells overlapped by the interstomatals (slightly). Intercostal short-cells common; in cork/silica-cell pairs (and solitary); silicified (occasionally only). Intercostal silica bodies rounded and tall-and-narrow. Crown cells absent (from the material seen, though it shows a few crown cell-like prickles near the margins). Costal short-cells neither distinctly grouped into long rows nor predominantly paired (solitary, paired and a few threes). Costal silica bodies crescentic; not sharp-pointed.

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 (there being a decidedly smaller rib intercalated between the large, round-topped ones towards the margin on either side). Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups (in the furrows); exclusively in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with all the main veins, the minor ones having small abaxial strands only); forming ‘figures’ (I’s to T’s in the main bundles). Sclerenchyma all associated with vascular bundles.

Phytochemistry. Tissues of the culm bases with little or no starch. Fructosans predominantly short-chain.

Cytology. Chromosome base number, x = 7. 2n = 56. 8 ploid. Nucleoli disappearing before metaphase.

Classification. Watson & Dallwitz (1994): Pooideae; Triticodae; Triticeae. Soreng et al. (2015): Pooideae; Triticodae; Triticeae; Hordeinae. 1 species (P. smithii).

Distribution, phytogeography, ecology. North America.

Mesophytic; halophytic (in heavy, saline-alkaline soils).

References, etc. Morphological/taxonomic: Löve 1984. Leaf anatomical: studied by us.

Special comments. Fruit data wanting. Illustrations. • P. smithii (as Agropyron): Hitchcock and Chase (1950). • P. smithii, 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: 11th December 2017.’.