| # The grass genera of the world |

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

### Streptostachys Desv.

Including Keratochlaena (= S. rigidifolia), Oncorachis

Habit, vegetative morphology. Perennial; decumbent. Culms 25–150(–200) cm high; herbaceous; branched above, or unbranched above. The branching simple. Culm nodes hairy, or glabrous. Culm internodes solid, or hollow. Leaves not basally aggregated; non-auriculate. Leaf blades broadly lanceolate, or ovate-lanceolate; broad; 7–30(–43) mm wide; cordate, or not cordate, not sagittate; not pseudopetiolate; without cross venation; persistent. Ligule present, or absent; when present, a fringe of hairs (sometimes with scattered hairs in the ligule position, and marginal tufts). Contra-ligule present (in S. macrantha).

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality. Plants without hidden cleistogenes.

Inflorescence. Inflorescence large, leafy, paniculate (its limits hard to define); open. Rachides sinuous. Inflorescence spatheate, or espatheate (?); a complex of ‘partial inflorescences’ and intervening foliar organs, or not comprising ‘partial inflorescences’ and foliar organs (? - with narrow secondary panicles and racemes). Spikelet-bearing axes ‘racemes’, or spikelike, or paniculate; persistent. Spikelets solitary, or paired; not secund; subsessile to pedicellate.

Female-fertile spikelets. Spikelets 3.6–9.3 mm long; narrowly oblong; abaxial (if ascertainable); compressed dorsiventrally; falling with the glumes; with a distinctly elongated rachilla internode between the glumes, with a distinctly elongated rachilla internode above the glumes, and with distinctly elongated rachilla internodes between the florets (the internodes thickened). The upper floret conspicuously stipitate. The stipe beneath the upper floret filiform (straight); homogeneous. Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; very unequal, or more or less equal; (at least the upper) long relative to the adjacent lemmas (more or less equalling the lower lemma); dorsiventral to the rachis; sparsely hairy (on the back); not pointed (blunt); awnless; non-carinate; very dissimilar to similar (herbaceous, the lower having its thickened base forming a downwardly projecting rim). Lower glume with short, sparse hairs; (1–)3–5(–7) nerved. Upper glume somewhat hooded apically; 5 nerved, or 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, or epaleate. Palea of the proximal incomplete florets (when present) fully developed to reduced. The proximal incomplete florets male, or sterile. The proximal lemmas awnless; (3–)5 nerved, or 7 nerved; more or less equalling the female-fertile lemmas; less firm than the female-fertile lemmas (membranous-herbaceous, sparsely hairy above); not becoming indurated.

Female-fertile florets 1. Lemmas decidedly firmer than the glumes (shiny); becoming indurated (thinly); entire; pointed; awnless; hairless; non-carinate; having the margins lying flat on the palea; with a clear germination flap; 5 nerved. Palea present; relatively long; entire; thinly indurated; indurated; 2-nerved; 2-keeled. Palea keels wingless. Lodicules present; 2; free; fleshy; glabrous; not or scarcely vascularized. Stamens 3. Anthers not penicillate; without an apically prolonged connective (the anthers divaricate). Ovary apically glabrous. Styles fused (S. asperifolia), or free to their bases. Stigmas dark.

Fruit, embryo and seedling. Fruit of S. macrostachya longitudinally grooved. Hilum long-linear. Embryo small (or "less than half the length of the caryopsis").

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; (36–)39–48 microns long; (4.8–)5.1–6.6(–6.9) microns wide at the septum. Microhair total length/width at septum 6.1–9.4. Microhair apical cells (18–)19–27(–33) microns long. Microhair apical cell/total length ratio 0.5–0.73. Stomata common; (28.5–)30–42 microns long. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; mostly cross shaped; not sharp-pointed.

Transverse section of leaf blade, physiology. C4 (S. macrantha, S. ramosa), or C3 (S. asperifolia); XyMS+. Mesophyll with radiate chlorenchyma, or with non-radiate chlorenchyma; with adaxial palisade (seemingly, in S. asperifolia), or without adaxial palisade; Isachne-type (perhaps, somewhat, in S. asperifolia), or not Isachne-type; with arm cells (a few); with fusoids (in S. asperifolia), or without fusoids. The fusoids external to the PBS. Leaf blade adaxially flat. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma (in the C4 species), or all the vascular bundles accompanied by sclerenchyma (S. asperifolia). Combined sclerenchyma girders present; forming ‘figures’ (I’s in S. macrantha, T’s in S. ramosa), or nowhere forming ‘figures’ (S. asperifolia). Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paspaleae; Paspalinae, or Arthropogoninae (?). 3 species.

Distribution, phytogeography, ecology. North tropical South America, Trinidad.

Savanna.

References, etc. Morphological/taxonomic: Morrone and Zuloaga 1991. Leaf anatomical: studied by us - S. asperifolia Desf.; Morrone and Zuloaga 1991.

Special comments. Streptostachys as carefully re-circumscribed by Morrone and Zuloaga (i.e. with ‘S. aucuminata’ referred to Urochloa, and ‘S. robusta’ excluded) continues to present a wonderful blend of panicoid and bambusoid features, and is very unusual in including both C3 and C4 species. Fruit data wanting.

Illustrations. • Strerptostachys macrantha, as Panicum vaginatum: Kunth (1835). • S. asperifolia, as S. hirsuta: P. Beauv. (1812). • Streptostachys asperifolia, abaxial epidermis of leaf blade: this project. • Streptostachys asperifolia, TS 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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