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The grass genera of the world

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

Torreyochloa Church

Habit, vegetative morphology. Perennial; stoloniferous, or caespitose. Culms 20–50 cm high; herbaceous. Culm internodes hollow. Leaves non-auriculate. Sheath margins free. Leaf blades linear; 1–2.5 mm wide; flat; not pseudopetiolate; rolled in bud. Ligule an unfringed membrane; not truncate; 0.5–5 mm long.

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

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

Female-fertile spikelets. Spikelets 2–6 mm long; compressed laterally to not noticeably compressed; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret. Hairy callus absent.

Glumes two; very unequal; shorter than the adjacent lemmas; not pointed (apically rounded); awnless; non-carinate; similar. Lower glume 1 nerved, or 3 nerved. Upper glume 1–3 nerved. Spikelets with female-fertile florets only, or with incomplete florets. The incomplete florets distal to the female-fertile florets. Spikelets without proximal incomplete florets.

Female-fertile florets 3–7. Lemmas decidedly firmer than the glumes; not becoming indurated; entire, or incised; when entire, blunt; when incised, not deeply cleft (denticulate); awnless; hairless; non-carinate; without a germination flap; 5–7 nerved (these prominent, scaberulous). Palea present; relatively long; 2-nerved; 2-keeled. Lodicules present; 2; free; membranous; glabrous; toothed, or not toothed; not or scarcely vascularized. Stamens 3. Anthers 0.3–0.6 mm long. Ovary apically glabrous (rarely), or apically hairy. Styles free to their bases. Stigmas 2; white.

Fruit, embryo and seedling. Fruit free from both lemma and palea; compressed laterally; with hairs confined to a terminal tuft. Hilum short. Embryo small. Endosperm hard; containing compound starch grains. Embryo with an epiblast; without a scutellar tail; with a negligible mesocotyl internode. Embryonic leaf margins meeting.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular, or fusiform; having straight or only gently undulating walls. Microhairs absent. Stomata common; 27–38 microns long. Subsidiaries parallel-sided. Guard-cells overlapped by the interstomatals. Intercostal short-cells absent or very rare. Costal short-cells neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies horizontally-elongated crenate/sinuous (mostly), or horizontally-elongated smooth (a few), or ‘panicoid-type’ (a few); sometimes nodular; not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups (in the furrows); in simple fans (the fans wide). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present. Sclerenchyma all associated with vascular bundles.

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

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

Distribution, phytogeography, ecology. Northern Asia, North America.

Helophytic; species of open habitats; glycophytic. Wet meadows and in shallow water.

References, etc. Leaf anatomical: this project.

Illustrations. • T. pallida (as Glyceria): Hitchcock and Chase (1950). • T. fernaldii (as Glyceria): Hitchcock and Chase (1950)


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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