| # The grass genera of the world |

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

### Oreochloa Link

~ Sesleria

Habit, vegetative morphology. Montane perennial; rhizomatous, or caespitose. Culms 15–40 cm high; herbaceous. Leaves non-auriculate. Sheath margins joined. Leaf blades linear; narrow; 0.5–2 mm wide; setaceous, or not setaceous; flat, or rolled (involute); without cross venation. Ligule an unfringed membrane; not truncate; 1–6 mm long.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant, or all alike in sexuality; hermaphrodite, or hermaphrodite and sterile (sometimes with small sterile bracts, representing reduced spikelets, at the base of the inflorescence); sometimes overtly heteromorphic (reduced and sterile/fertile).

Inflorescence. Inflorescence paniculate; contracted; more or less ovoid, or spicate; espatheate (ignoring any basal ‘bracts’); not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets secund, or not secund; unilateral or distichous; pedicellate.

Female-fertile spikelets. Spikelets 3–6 mm long; compressed laterally; disarticulating above the glumes. Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension with incomplete florets. Hairy callus absent.

Glumes two; very unequal, or more or less equal; shorter than the adjacent lemmas; pointed (acute); awnless; non-carinate; similar. Lower glume 1(–3) nerved. Upper glume 1(–3) nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets.

Female-fertile florets 3–7. Lemmas similar in texture to the glumes (membranous); not becoming indurated; entire, or incised; when incised, 3 lobed (3-toothed); not deeply cleft; awnless, or mucronate; hairy; carinate; without a germination flap; obscurely 5–7 nerved. Palea present; relatively long; 2-nerved; 2-keeled. Palea keels hairy (ciliate). Lodicules present; 2; free; membranous; glabrous; toothed, or not toothed; not or scarcely vascularized. Stamens 3. Anthers 2–3.5 mm long. Ovary apically glabrous; without a conspicuous apical appendage. Styles fused. Stigmas 2.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small (2 mm long). Hilum short. Embryo small; with an epiblast; without a scutellar tail; with a negligible mesocotyl internode. Embryonic leaf margins meeting.

Abaxial leaf blade epidermis. Costal/intercostal zonation lacking. Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls (thick and pitted). Microhairs absent. Stomata absent or very rare. Intercostal short-cells common; not paired; not silicified. Costal short-cells neither distinctly grouped into long rows nor predominantly paired (mostly solitary). Costal silica bodies absent (in the material seen).

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma. Leaf blade with distinct, prominent adaxial ribs, or ‘nodular’ in section; with the ribs more or less constant in size. Midrib conspicuous (larger bundle and rib); with one bundle only. Bulliforms present in discrete, regular adaxial groups (as well as the ‘midrib hinges’ and Ammophila-type arrangements of small cells in the furrows); in simple fans (sin some of the furrows). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent (each bundle with adaxial and abaxial strands). Sclerenchyma all associated with vascular bundles, or not all bundle-associated.

Cytology. Chromosome base number, x = 7. 2n = 14. 2 ploid. Chromosomes ‘large’.

Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Seslerieae. Soreng et al. (2015): Pooideae; Poodae; Poeae; Sesleriinae. 4 species.

Distribution, phytogeography, ecology. Southern Europe.

Species of open habitats. Mountain rocks, calcifuge.

Rusts and smuts. Smuts from Tilletiaceae. Tilletiaceae — Entyloma.

References, etc. Leaf anatomical: studied by us - O. disticha (Wulf.) Link.

Illustrations. • Oreochloa disticha, as Sesleria confusa: Coincy (1897), Ecloga plantarun Hispanicum 3.

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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