Grass Genera of the World

L. Watson and M. J. Dallwitz

Stenotaphrum Trin.

From the Greek stenos (narrow) and taphros (trench), alluding to cavities in rachides.

Including Diastemenanthe Steud., Ophiurinella Desv.

Habit, vegetative morphology. Annual, or perennial; rhizomatous, or stoloniferous, or caespitose. Culms 10–60 cm high; herbaceous; branched above. Culm nodes glabrous. Leaves not basally aggregated; non-auriculate. The sheaths compressed. Leaf blades lanceolate to elliptic; broad, or narrow; flat, or folded (when young); pseudopetiolate, or not pseudopetiolate; without cross venation; disarticulating from the sheaths, or persistent (rarely); once-folded in bud; ligule present; a fringed membrane.

Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality.

Inflorescence. Inflorescence of spicate main branches, or a false spike, with spikelets on contracted axes (the spikelets 1 to several, in very short spike-like racemes embedded in hollows of the corky or foliaceous common axis, or in longer racemes closely appressed to it); non-digitate. Primary inflorescence branches borne biseriately on one side of the main axis, or borne distichously. Inflorescence axes not ending in spikelets (minutely bare-tipped, when not coalesced with the main axis). Rachides hollowed. Inflorescence spatheate (the small racemes subtended/enclosed by spathes which are laterally adnate to the rachis), or espatheate; a complex of ‘partial inflorescences’ and intervening foliar organs, or not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes very much reduced (sometimes reduced to one spikelet with no rachis extension, or coalesced with the main axis); disarticulating; falling entire (the free racemes falling with the joint of the main axis), or disarticulating at the joints (when the ‘spikelet bearing unit’ consists of a coalesced main axis and branches). Spikelets unaccompanied by bractiform involucres, not associated with setiform vestigial branches; secund.

Female-fertile spikelets. Spikelets elliptic, or lanceolate, or ovate; abaxial; compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; very unequal; (the longer) long relative to the adjacent lemmas, or shorter than the adjacent lemmas; dorsiventral to the rachis; awnless; very dissimilar (lower minute, scale-like, upper large, substantial), or similar (both small, scale-like). Lower glume 0 nerved. Upper glume 5–9 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. The proximal incomplete florets male, or sterile (rarely). The proximal lemmas awnless; 3 nerved, or 7–9 nerved; similar in texture to the female-fertile lemmas, or decidedly firmer than the female-fertile lemmas (leathery or papery); not becoming indurated.

Female-fertile florets 1. Lemmas decidedly firmer than the glumes (papery to subleathery); smooth to striate; not becoming indurated; yellow in fruit; entire; pointed; awnless; hairless; non-carinate; having the margins lying flat on the palea; with a clear germination flap; 3–5 nerved. Palea present; relatively long; entire (pointed); awnless, without apical setae; textured like the lemma; not indurated; 2-nerved. Lodicules present; 2; fleshy. Stamens 3. Anthers not penicillate. Ovary glabrous. Styles fused. Stigmas 2; white, or red pigmented.

Fruit, embryo and seedling. Disseminule comprising the rachis segment and associated structures, or consisting of the disarticulated spikelet-bearing inflorescence unit, or constituted by the complete, deciduous inflorescence. Fruit small; ellipsoid; compressed dorsiventrally. Hilum short. Embryo large; not waisted.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; (45–)54–78(–84) microns long; 9–12(–13.5) microns wide at the septum. Microhair total length/width at septum 6.2–7.7. Microhair apical cells 32–62 microns long. Microhair apical cell/total length ratio 0.61–0.76. Stomata common; (27–)28.5–30(–33) microns long. Subsidiaries low dome-shaped, or triangular, or dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs and not paired (solitary); silicified, or not silicified. Intercostal silica bodies when present, tall-and-narrow. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; cross shaped to dumb-bell shaped, or nodular; not sharp-pointed.

Transverse section of leaf blade, physiology. C4; XyMS–. PCR sheath outlines uneven. PCR sheath extensions absent. PCR cell chloroplasts with reduced grana; centrifugal/peripheral. Mesophyll with radiate chlorenchyma. Leaf blade adaxially flat; with the ribs more or less constant in size. Midrib conspicuous; having a conventional arc of bundles; without colourless mesophyll adaxially (but with colourless cells abaxially instead, here and sometimes with other main bundles). Bulliforms not present in discrete, regular adaxial groups (absent or irregularly disposed, apart from a group over the midrib). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders absent. Sclerenchyma all associated with vascular bundles.

Cytology. Chromosome base number, x = 9. 2n = 18, 20, and 36. 2 and 4 ploid.

Taxonomy. Panicoideae; Panicodae; Paniceae.

Distribution, ecology, phytogeography. 7 species; tropical and subtropical. Commonly adventive. Mesophytic; species of open habitats; halophytic, or glycophytic. Usually in sandy soils near the coast, sometimes inland.

Holarctic, Paleotropical, Neotropical, Cape, and Australian. Boreal. African, Madagascan, Indomalesian, Polynesian, and Neocaledonian. Atlantic North American. Sudano-Angolan. Indian, Indo-Chinese, Malesian, and Papuan. Fijian. Caribbean, Central Brazilian, Pampas, and Andean. North and East Australian. Southern Atlantic North American and Central Grasslands. Sahelo-Sudanian, Somalo-Ethiopian, and South Tropical African. Tropical North and East Australian.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia stenotaphri and ‘Uromycessetariae-italicae. Smuts from Ustilaginaceae. Ustilaginaceae — Sorosporium, Sphacelotheca, and Ustilago.

Economic importance. Significant weed species: S. dimidiatum, S. secundatum. Important native pasture species: S. dimidiatum, S. secundatum. Lawns and/or playing fields: S. secundatum (in warm coastal regions).

References, etc. Morphological/taxonomic: Saur 1972. Leaf anatomical: Metcalfe 1960; this project.

Illustrations. • General aspect, spikelet. • General aspect. • Inflorescence detail. Stenotaphrum secundatum. • Abaxial epidermis of leaf blade. • Abaxial epidermis of leaf blade. • Pollen antigens

Cite this publication as: Watson, L., and Dallwitz, M. J. (1992 onwards). ‘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: 18th August 1999. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993 onwards, 1998), and Watson and Dallwitz (1994), and Watson, Dallwitz, and Johnston (1986) should also be cited (see References).