| # The grass genera of the world |

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

### Psathyrostachys Nevski

From the Greek psathyros (weak, crumbling) and stachys (spike, ‘ear’ of wheat), alluding to fragility of the rachis.

Habit, vegetative morphology. Perennial (with short, creeping rhizomes). Culms 15–100 cm high; herbaceous; unbranched above. Culm internodes hollow. Young shoots intravaginal. Leaves mostly basal, or not basally aggregated; auriculate (usually, at least some of them), or non-auriculate. Sheath margins joined (ramal leaves), or free (cauline leaves). Leaf blades narrowly linear; narrow; 1–4.5 mm wide; folded, or rolled; without cross venation; persistent. Ligule an unfringed membrane; truncate; 0.1–1 mm long. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality (?). Plants outbreeding.

Inflorescence. Inflorescence a false spike, with spikelets on contracted axes (linear, erect); espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes disarticulating; disarticulating at the joints. Spikelets paired, or in triplets, or paired and in triplets; not secund; distichous (the groups distichously arranged on the rachis); sessile.

Female-fertile spikelets. Spikelets 6–16 mm long; compressed laterally to compressed dorsiventrally (?); falling with the glumes; not disarticulating between the florets (the rachilla without joints). Rachilla prolonged beyond the uppermost female-fertile floret; hairy (bristly), or hairless; the rachilla extension with incomplete florets.

Glumes two; more or less equal; free; displaced (borne side by side); densely hairy or scabrid; subulate (subulate-setiform); awned (awn-like); non-carinate; similar (subulate). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with incomplete florets (?). The incomplete florets distal to the female-fertile florets (above the perfect floret(s)). The distal incomplete florets 1; merely underdeveloped. Spikelets without proximal incomplete florets.

Female-fertile florets 1, or 2. Lemmas entire; acuminate pointed; mucronate to awned. Awns 1; median; apical; non-geniculate; much shorter than the body of the lemma to much longer than the body of the lemma (up to 8 mm long). Lemmas non-carinate (dorsally broadly rounded); without a germination flap; 5–7 nerved; with the nerves confluent towards the tip. Palea present; relatively long; 2-nerved; 2-keeled. Lodicules present; 2; free; membranous; ciliate; not toothed (entire); not or scarcely vascularized. Stamens 3. Anthers 1–6 mm long. Ovary apically hairy. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit adhering to lemma and/or palea; small to medium sized (3–7.5 mm long); longitudinally grooved; compressed dorsiventrally; with hairs confined to a terminal tuft. Hilum long-linear. Embryo small.

Seedling with a loose coleoptile.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells differing markedly in wall thickness costally and intercostally (costal walls thicker). Mid-intercostal long-cells rectangular; having straight or only gently undulating walls. Microhairs absent. Stomata common. Subsidiaries parallel-sided. Guard-cells overlapped by the interstomatals (sunken). Intercostal short-cells absent or very rare (their presence excluded by the abundance of prickles). Prickles abundant. Costal short-cells neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies horizontally-elongated crenate/sinuous (large), or horizontally-elongated smooth; not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans (these large, in the furrows). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders absent (abaxial only). 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 = 14. 2 ploid. Haplomic genome content N. Chromosomes ‘large’.

Classification. Watson & Dallwitz (1994): Pooideae; Triticodae; Triticeae. Soreng et al. (2015): Pooideae; Triticodae; Triticeae; Hordeinae. 8 species.

Distribution, phytogeography, ecology. Asia and Southeast Europe.

Xerophytic; species of open habitats. Steppe and semi-desert regions, stony slopes.

Hybrids. Intergeneric hybrids with Leymus (×Leymostachys Tsvelev). See also ×Elymostachys Tsvelev.

References, etc. Morphological/taxonomic: Löve 1984. Leaf anatomical: Metcalfe 1960; studied by us - P. junceus (Fischer) Nevski.

Illustrations. • Psathyrostachys fragilis: Bor, Fl. of Iraq (1968). • Psathyrostachys junceus, 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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