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The grass genera of the world

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

Orinus A. Hitchc.

From the Greek oreinos (a mountaineer), alluding to habitat.

Habit, vegetative morphology. Perennial; rhizomatous and caespitose. Culms 30–50 cm high; herbaceous. Rhizomes pachymorph. Plants unarmed. Leaves non-auriculate. Leaf blades narrow; 2–5 mm wide (by 3–10 cm long, sparsely pilose); becoming involute; with setiform, slightly pungent tips; exhibiting multicellular glands abaxially. The abaxial leaf blade glands intercostal. Leaf blades not pseudopetiolate; without cross venation. Ligule thin, lacerate; 1 mm long.

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

Inflorescence. Inflorescence of spicate main branches (erect or ascending racemes); non-digitate (the axis elongate). Primary inflorescence branches 5–8. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; secund (the rachides dorsiventral); not two-ranked (in one row, on one side of the rachis, appressed); shortly pedicellate.

Female-fertile spikelets. Spikelets 6 mm long; pale or leaden-purplish tinged; disarticulating above the glumes; disarticulating between the florets; with distinctly elongated rachilla internodes between the florets (a 1 mm internode between the first and second florets). Rachilla prolonged beyond the uppermost female-fertile floret; hairless (glabrous).

Glumes two; relatively large (4–5 mm long); more or less equal (only slightly unequal); shorter than the adjacent lemmas; hairy (sparsely villous to nearly glabrous); without conspicuous tufts or rows of hairs; pointed (acute); awnless; similar (pale, membranous). Lower glume shorter than the lowest lemma; 1 nerved. Upper glume 3 nerved. Spikelets with female-fertile florets only, or 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 2–3 (-4). Lemmas similar in texture to the glumes (the tips hyaline); not becoming indurated; entire; blunt, or pointed; awnless, or mucronate (but only slightly so); hairy (with villous hairs all over, not confined to the nerves as in Leptochloa and Trichoneura); indistinctly carinate; 3 nerved (somewhat concave between the nerves). Palea present; relatively long; awnless, without apical setae; 2-keeled. Palea keels hairy. Stamens 3; with free filaments. Anthers 2.5–2.75 mm long. Stigmas 2.

Fruit, embryo and seedling. Fruit small (2.5 mm long); not noticeably compressed (cylindrical). Hilum short. Pericarp fused. Embryo large (about 1/3 the grain length).

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present (very abundant); costal and intercostal. Intercostal papillae over-arching the stomata; consisting of one symmetrical projection per cell. Intercostal zones with typical long-cells (or these rather short). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs 21–24–25.5 microns long. Microhair basal cells 24 microns long. Microhairs (9.3–)10.5–11.4(–15) microns wide at the septum. Microhair total length/width at septum 1.6–2.6. Microhair apical cells 10.5–12–16.5 microns long. Microhair apical cell/total length ratio 0.41–0.68. Stomata common (alongside the veins); 21–22.5(–25.5) microns long. Subsidiaries triangular (though not readily observable). Intercostal short-cells common; in cork/silica-cell pairs and not paired (some solitary); not silicified. Intercostal silica bodies absent. Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; ‘panicoid-type’; limited to cross shaped and butterfly shaped; not sharp-pointed.

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 absent. Leaf blade ‘nodular’ in section to adaxially flat. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans (these predominating, with large, deeply penetrating median cells), or associated with colourless mesophyll cells to form deeply-penetrating fans (a few). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with all the bundles); forming ‘figures’ (all bundles with small I’s). 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. 2 species.

Distribution, phytogeography, ecology. Western Himalayas.

Xerophytic; species of open habitats. Desert sand dunes at high altitude.

References, etc. Morphological/taxonomic: Hitchcock 1933. Leaf anatomical: this project.

Illustrations. • O. thoroldii, abaxial epidermis of leaf blade: this project. • O. thoroldii, TS leaf blade including midrib region: 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: 13th November 2017. delta-intkey.com/grass’.

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