| # The grass genera of the world |

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

### Halopyrum Stapf

Habit, vegetative morphology. Perennial; stoloniferous and caespitose. Culms herbaceous (tough); sparsely branched above. The branching simple. Leaves non-auriculate. Leaf blades narrow (junciform); rolled (convolute, stiff, filiform-tipped); not needle-like; without abaxial multicellular glands; not pseudopetiolate; without cross venation; disarticulating from the sheaths. Ligule a fringe of hairs.

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

Inflorescence. Inflorescence of spicate main branches (the short, erect branches being themselves unbranched), or paniculate (elongated, contracted); non-digitate; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; not secund.

Female-fertile spikelets. Spikelets 10–30 mm long; compressed laterally; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; hairy (the internodes bearded at the tip, with long hairs up to half the lemma length); the rachilla extension with incomplete florets. Hairy callus present.

Glumes two; more or less equal (subequal); shorter than the spikelets; shorter than the adjacent lemmas to long relative to the adjacent lemmas; hairless; pointed (acuminate); awnless; carinate; similar (leathery, ovate-lanceolate). Lower glume shorter than the lowest lemma to about equalling the lowest lemma; 3–5 nerved. Upper glume 5–7 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped.

Female-fertile florets 6–20. Lemmas ovate-oblong, acute; similar in texture to the glumes (leathery); entire, or incised; pointed; if incised 2 lobed; not deeply cleft (bidenticulate); mucronate; hairy (asperulous or minutely hairy); carinate; 3 nerved. Palea present; relatively long; entire; awnless, without apical setae; 2-nerved; 2-keeled (the keels scaberulous). Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit ellipsoid; longitudinally grooved; compressed dorsiventrally (concavo-convex). Hilum short. Pericarp fused. Embryo large; with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins meeting.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present (in the deep grooves, and abundant adaxially); intercostal. Intercostal papillae over-arching the stomata; consisting of one oblique swelling per cell, or consisting of one symmetrical projection per cell (finger-like). Long-cells differing markedly in wall thickness costally and intercostally (the costals thick-walled). Microhairs present (in deep intercostal grooves); more or less spherical; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs 27–33–34.5 microns long; 21–22.5 microns wide at the septum. Microhair total length/width at septum 1.2–1.6. Microhair apical cells 17.4–27 microns long. Microhair apical cell/total length ratio 0.54–0.78. Stomata absent or very rare. Intercostal silica bodies absent. Costal short-cells neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies present throughout the costal zones; saddle shaped (mainly), or tall-and-narrow, or ‘panicoid-type’ (a few).

Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.

C4; XyMS+. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only. PCR sheath extensions present. Maximum number of extension cells 1–5. Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells. Leaf blade ‘nodular’ in section; with the ribs very irregular in sizes. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans and associated with colourless mesophyll cells to form deeply-penetrating fans (sometimes linked with traversing columns of colourless cells). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae. 1 species (H. mucronatum).

Distribution, phytogeography, ecology. Coastal Indian Ocean.

Xerophytic; species of open habitats; halophytic. A coastal sand stabilizer.

References, etc. Morphological/taxonomic: Stapf 1896. Leaf anatomical: studied by us.

Illustrations. • Halopyrum mucronatum: Hook. Ic. Pl 25 (1896).

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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