| # The grass genera of the world |

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

### Otachyrium Nees

Habit, vegetative morphology. Perennial; rhizomatous and caespitose. Culms 20–150 cm high; herbaceous; branched above, or unbranched above. The branching simple. Culm nodes hairy (usually). The shoots not aromatic. Leaves not basally aggregated; non-auriculate. Leaf blades linear to linear-lanceolate; narrow; 1–9 mm wide; setaceous, or not setaceous; flat, or rolled, or acicular; without cross venation. Ligule a fringed membrane; truncate.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets, or without hermaphrodite florets (the upper floret may be female-only in two species). The spikelets all alike in sexuality.

Inflorescence. Inflorescence of spicate main branches, or paniculate; open, or contracted; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets paired (usually); not secund; not two-ranked; pedicellate. Pedicel apices cupuliform. Spikelets consistently in ‘long-and-short’ combinations; unequally pedicellate in each combination.

Female-fertile spikelets. Spikelets 2–8.5 mm long; compressed laterally to compressed dorsiventrally; falling with the glumes; with conventional internode spacings. The upper floret not stipitate. Rachilla terminated by a female-fertile floret (though one species occasionally has a third, terminal, abortive floret). Hairy callus absent.

Glumes two; more or less equal (subequal); shorter than the spikelets (1/4 to 1/2 as long); shorter than the adjacent lemmas; hairy, or hairless; awnless; carinate; similar (membranous). Lower glume 1–3 nerved. Upper glume 1–7 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; paleate. Palea of the proximal incomplete florets fully developed; becoming conspicuously hardened and enlarged laterally (greatly enlarged and often winged, expanding widely beyond the spikelet when mature, and adhering to the upper floret). The proximal incomplete florets male. The proximal lemmas sometimes sulcate; awnless; 3 nerved; more or less equalling the female-fertile lemmas to decidedly exceeding the female-fertile lemmas; less firm than the female-fertile lemmas (membranous); not becoming indurated.

Female-fertile florets 1. Lemmas acute; decidedly firmer than the glumes; smooth (and shining), or striate; becoming indurated to not becoming indurated (from papery to crustaceous); pallid to black; entire; pointed; awnless; hairless; non-carinate (convex or gibbous); having the margins inrolled against the palea; without a germination flap; 3–5 nerved. Palea present; relatively long; entire; awnless, without apical setae; textured like the lemma; indurated, or not indurated; 2-nerved; 2-keeled. Palea keels winged (in four of the species), or wingless. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit small (1.5 – 2.5 mm long); ellipsoid; compressed dorsiventrally (plano-convex). Hilum short. Embryo large; not waisted.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals longer and narrower); of similar wall thickness costally and intercostally (quite thin walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; 34.5–36–42 microns long; 7.5–9 microns wide at the septum. Microhair total length/width at septum 4–5.6. Microhair apical cells 21–24–27 microns long. Microhair apical cell/total length ratio 0.57–0.75. Stomata common; (30–)36–42 microns long. Subsidiaries mostly triangular (low, with small points). Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; not paired (solitary); not silicified. Intercostal prickles abundant. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; cross shaped, dumb-bell shaped, and nodular; not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll without adaxial palisade; with fusoids (?- a suspicion of these, not confirmable in available material). Leaf blade ‘nodular’ in section to adaxially flat. Midrib conspicuous; with one bundle only, or having a conventional arc of bundles (depending on the limits set on the midrib); with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with the main bundles); forming ‘figures’ (the main bundles with small I’s). Sclerenchyma all associated with vascular bundles.

Cytology. Chromosome base number, x = 9; 2 ploid.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paspaleae; Otachyriinae. 7 species.

Distribution, phytogeography, ecology. Tropical South America, West Indies.

Helophytic, or mesophytic; glycophytic.

References, etc. Morphological/taxonomic: Sendulsky and Soderstrom 1984. Leaf anatomical: studied by us - O. succisum (Swallen) Sendulsky & Soderstrom.

Illustrations. • Otachyrium versicolor: Nicora & Rúgolo de Agrasar (1987).

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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