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The grass genera of the world

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

Streptochaeta Schrad.

Including Lepideilema Trin.

Habit, vegetative morphology. Perennial; rhizomatous (the internodes crowded). The flowering culms leafy. Culms 35–105 cm high; woody and persistent; to 0.3 cm in diameter; branched above, or unbranched above. The branching simple. Culm nodes glabrous. Culm internodes hollow. Pluricaespitose. Rhizomes pachymorph. Plants unarmed. Leaves not basally aggregated; spirally disposed; auriculate (from the sheath); with auricular setae. The juncture of blade and sheath a smooth, dark band of tissue covered by cilia abaxially. Leaf blades lanceolate to ovate; broad; (5–)10–95 mm wide; pseudopetiolate; palmately veined to pinnately veined (in that the veins converge into the midrib from a distance of several cm above the base of the lamina); cross veined; disarticulating from the sheaths. Ligule a fringe of hairs. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. Not viviparous.

Inflorescence. Inflorescence determinate; with pseudospikelets, or without pseudospikelets (depending on interpretation: buds sometimes present in the ‘bract’ axils, but these seemingly not proliferating); a single raceme (or a raceme of spikes, if the ‘spikelet’ be so interpreted). Inflorescence with axes ending in spikelets, or axes not ending in spikelets (sometimes ending in a tuft of hairs). Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes spikes; persistent (tough). Spikelets solitary; not secund; not two-ranked (the raceme many-sided); pedicellate. Pedicel apices cupuliform.

Female-fertile spikelets. Spikelets unconventional (with 5 spirally arranged, dentate ‘bracts’ (?glumes, sometimes with axillary buds), a sixth produced into a very long, coiled awn, 7 and 8 side by side opposing 6, and 9–11 whorled to form a central cone, lemma, palea and lodicules absent); 10–20 mm long; not noticeably compressed; falling with the glumes (all the pseudospikelets of the inflorescence often shed as a unit, entangled via the long awns of their G6’s which are deflected by the central cones into the cleft between bracts 7 and eight). Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes present; several (in the form of 11 or twelve ‘bracts’, as described elsewhere, the lowermost to 4 mm long, the uppermost to 15 mm); very unequal; hairless; awned (the G6 with a long, coiled, terminal awn), or awnless (the rest); non-carinate. Spikelets with female-fertile florets only.

Female-fertile florets 1. Lemmas absent, or at least unrecognisable. Palea present; convolute around the flower, or not convolute. Lodicules absent. Stamens 6; monadelphous. Anthers not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles fused. Stigmas 3.

Fruit, embryo and seedling. Fruit free from both lemma and palea; linear; not grooved; not noticeably compressed (terete). Hilum long-linear. Pericarp loosely adherent to fused. Embryo small. Endosperm hard; containing compound starch grains. Embryo without an epiblast; with a scutellar tail; with a negligible mesocotyl internode; with more than one scutellum bundle. Embryonic leaf margins overlapping.

Seedling with a short mesocotyl; with a loose coleoptile. First seedling leaf without a lamina.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells of similar wall thickness costally and intercostally (walls of medium thickness). Mid-intercostal long-cells rectangular and fusiform (but the latter forms asymmetric, reflecting oblique end-walls); having markedly sinuous walls. Microhairs present; panicoid-type; (84–)90–96(–99) microns long; (6–)7.5–9 microns wide at the septum. Microhair total length/width at septum 9.3–13.2. Microhair apical cells (43.5–)58.5–66(–69) microns long. Microhair apical cell/total length ratio 0.52–0.72. Stomata common; 24–33 microns long. Subsidiaries high dome-shaped, or parallel-sided. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare. Costal short-cells neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies exclusively saddle shaped; not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without arm cells (or at least without conspicuous arm cells, in the material seen); with fusoids. The fusoids external to the PBS. Leaf blade adaxially flat. Midrib conspicuous (via a T-shaped adaxial rib and a small, rounded, abaxial keel); having complex vascularization (there being a small bundle adaxial to the main one); with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups (these large and wide); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles.

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

Classification. Watson & Dallwitz (1994): Bambusoideae; Bambusodae; Streptochaeteae. Soreng et al. (2015): Anomochlooideae; Streptochaeteae. 3 species.

Distribution, phytogeography, ecology. Mexicoto Argentina.

Shade species.

References, etc. Morphological/taxonomic: Judziewicz and Soderstrom 1989. Leaf anatomical: Metcalfe 1960; this project.

Illustrations. • S. spicata, general aspect: Trinius (1836), Species Graminum 3. • S. spicata, technical details: Trinius (1836), Species Graminum 3. • S. spicata: Nicora & Rúgolo de Agrasar (1987)


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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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