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The grass genera of the world

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

Ortachne Nees ex Steud.

~ Stipa, cf. Lorenzochloa

Excluding Lorenzochloa

Habit, vegetative morphology. Perennial. Culms 5–35 cm high (?); herbaceous; unbranched above. Leaf blades filiform; narrow; rolled and acicular; without cross venation.

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

Inflorescence. Inflorescence many spikeleted (at least, usually of 10 or more, by contrast with Aciachne); paniculate (borne well above the leaves); open; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets not noticeably compressed (the floret cylindrical); disarticulating above the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present. Callus short; pointed.

Glumes two; shorter than the spikelets; shorter than the adjacent lemmas; pointed, or not pointed (truncate or acute); awnless; similar (membranous). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only.

Female-fertile florets 1. Lemmas covering only the margins of the palea; not convolute; not saccate; without a crown; similar in texture to the glumes (membranous); not becoming indurated; entire; awned. Awns 1; median; apical (from the acuminate lemma); non-geniculate; persistent. Awn bases slightly twisted. Lemmas non-carinate; 5 nerved. Palea present; relatively long; prow-tipped, or not prow-tipped (?); membranous; 2-nerved; keel-less, or one-keeled (?). Lodicules present; 3. Stamens 3.

Abaxial leaf blade epidermis. Costal/intercostal zonation lacking. Papillae absent (though abundant adaxially). Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally (thick walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls (these very heavily pitted). Microhairs absent. Stomata absent or very rare (seen adaxially only, with parallel-sided subsidiaries). Intercostal short-cells common. Costal short-cells neither distinctly grouped into long rows nor predominantly paired (frequently in short rows). Costal silica bodies seemingly ‘panicoid-type’ (but very hard to observe in the material available); not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Leaf blade with distinct, prominent adaxial ribs; with the ribs very irregular in sizes. Midrib not readily distinguishable; with one bundle only. Bulliforms not present in discrete, regular adaxial groups (not seen). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with the primaries); forming ‘figures’. Sclerenchyma not all bundle-associated. The ‘extra’ sclerenchyma in a continuous abaxial layer (this submerging the ‘feet’ of the ‘anchors’).

Cytology. Chromosome base number, x = 11. 2n = 22. 2 ploid.

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

Distribution, phytogeography, ecology. Chile.

Xerophytic; species of open habitats. Montane.

References, etc. Morphological/taxonomic: Hughes 1923; Reeder and Reeder 1968. Leaf anatomical: this project.

Special comments. Fruit data wanting. Illustrations. • O. rariflora (as Muhlenbergia): Hooker, Fl. Antarctica (1844)


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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