| # The grass genera of the world |

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

### Trikeraia Bor

~ Stipa

Including Stipa sect. Lasiagrostis (Link) Hackel, Achnatherum sect. Trikeraia (Bor) Tsvelev (see Freitag 1985)

Habit, vegetative morphology. Perennial; caespitose. Culms 7.5–20 cm high (T. oreophila), or 60–70(–90) cm high (T. hookeri); herbaceous. Young shoots intravaginal. Leaves non-auriculate. Leaf blades narrow; 1–1.5 mm wide; flat, or rolled (convolute or involute); not pseudopetiolate; without cross venation; persistent. Ligule an unfringed membrane, or a fringed membrane (T. hookeri); truncate; 0.4 mm long (T. oreophila), or 2 mm long (T. hookeri).

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

Inflorescence. Inflorescence paniculate; open, or contracted; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets 7.5–11 mm long; slightly compressed dorsiventrally, or not noticeably compressed; disarticulating above the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present. Callus short (0.5 mm long in T. hookeri); blunt.

Glumes two; more or less equal; about equalling the spikelets, or exceeding the spikelets; long relative to the adjacent lemmas; awnless (sometimes mucronate); non-carinate; very dissimilar to similar (lanceolate, the upper sometimes with a 0.5 mm mucro and two short lobes). Lower glume 3 nerved (T. hookeri), or 5 nerved (T. oreophila). Upper glume 3 nerved. Spikelets with female-fertile florets only; without proximal incomplete florets.

Female-fertile florets 1. Lemmas not convolute (covering only the sides of the palea); without a crown; decidedly firmer than the glumes (membranous); not becoming indurated; incised; 2 lobed (dissected into two conspicuous, acuminate or shortly awned lobes); not deeply cleft; awned. Awns 1 (T. oreophila), or 3; median, or median and lateral (T. hookeri with two short straight lateral awns in addition to the median one); (the median) different in form from the laterals; from a sinus; non-geniculate to geniculate (indistincly unigeniculate in T. hookeri); hairless (scabrous); about as long as the body of the lemma to much longer than the body of the lemma; entered by several veins (3); persistent. The lateral awns of T. hookeri shorter than the median. Awn bases somewhat twisted. Lemmas hairy (on the back, the lobes glabrous); non-carinate; having the margins lying flat on the palea; 3–7 nerved. Palea present; relatively long (slightly shorter than the lemma); not prow-tipped; entire (acute); thinner than the lemma (hyaline); not indurated; 2-nerved; keel-less. Palea back hairy (hairy down the middle like the lemma). Lodicules present; 3. Third lodicule present. Lodicules free; membranous (two ‘stipoid’ and fleshy at the base); glabrous; toothed, or not toothed (?); heavily vascularized. Stamens 3. Anthers 1–1.5 mm long (T. oreophila), or 4–4.5 mm long (T. hookeri); not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; costal and intercostal. Intercostal papillae over-arching the stomata (and obscuring them); several per cell (small, in longitudinal rows on the long-cells). Mid-intercostal long-cells having markedly sinuous walls. Microhairs absent (also absent adaxially). Stomata common; 33–39 microns long. Subsidiaries non-papillate. Intercostal short-cells common; in cork/silica-cell pairs. Costal zones with short-cells. Costal short-cells neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies ‘panicoid-type’; dumb-bell shaped to nodular; not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma. Leaf blade with distinct, prominent adaxial ribs. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups (restricted to the bases of the furrows, small and irregular, cf. Ammophila). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma not all bundle-associated. The ‘extra’ sclerenchyma in a continuous abaxial layer.

Classification. Watson & Dallwitz (1994): Stipoideae; Stipeae. Soreng et al. (2015): Pooideae; Stipeae. 2 species.

Distribution, phytogeography, ecology. Pakistan to Tibet.

Species of open habitats; glycophytic. Montane, by water.

References, etc. Morphological/taxonomic: Bor 1955; Macfarlane and Watson 1980; Freitag 1985; Cope 1988. Leaf anatomical: Metcalfe 1960; studied by us - T. hookeri (Stapf) Bor.

Special comments. Fruit data wanting.

Illustrations. • Trikeraia hookeri and T. pappiformis: Fl. Rep. Pop. Sin. (2016). • Trikeraia hookeri, 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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