Grass Genera of the World

L. Watson and M. J. Dallwitz

Trachys Pers.

Including Trachyozus Reichenb., Trachystachys Dietr.

Habit, vegetative morphology. Diffuse annual; decumbent. Culms 15–30 cm high; herbaceous. Culm nodes hairy. Leaves not basally aggregated; non-auriculate. Leaf blades narrow, or broad; 6–12 mm wide (by 2.5–5 cm long); without cross venation; persistent; a fringe of hairs; 3 mm long.

Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite and sterile, or hermaphrodite, male-only, and sterile (the clusters of complete spikelets surrounded by incomplete ones); overtly heteromorphic (each cluster with proximal barren spikelets, the outermost reduced to thickened, rigid bracts or recurved spines).

Inflorescence. Inflorescence of spicate main branches (of one-sided, winged, spikelike racemes, the underside of each bearing alternating, short-peduncled glomerules, the latter containing 2–3 bisexual spikelets plus ‘bracts’ and spines); usually digitate. Primary inflorescence branches (1–)2–3. Rachides winged. Spikelet-bearing axes very much reduced (to glomerules); disarticulating; falling entire (the glomerules constituting burrs, which fall with the rachis joint, i.e. the main rachides also disarticulate). Spikelets associated with bractiform involucres (spiny, representing the variously reduced sessile/subsessile spikelets surrounding the clusters). The involucres shed with the fertile spikelets. Spikelets secund (the clusters from the midrib on one side of the broad, flat, jointed rachis); subsessile.

Female-fertile spikelets. Spikelets unconventional (or hard to interpret, because of the associated involucral spikelets); 5–6 mm long; compressed dorsiventrally; falling with the glumes (within the cluster). Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; very unequal; shorter than the spikelets; shorter than the adjacent lemmas; the upper hairy; pointed (acuminate); awnless; non-carinate; very dissimilar (the lower small, subulate-lanceolate and glabrous, the upper membranous and lanceolate, hairy). Lower glume 0 nerved. Upper glume 3 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 reduced (tiny). The proximal incomplete florets sterile. The proximal lemmas expanded to form a broadly ovate, involucral scale; awnless (acute); 11–17 nerved; decidedly exceeding the female-fertile lemmas; decidedly firmer than the female-fertile lemmas (leathery); becoming indurated.

Female-fertile florets 1. Lemmas ovate-lanceolate to linear-oblong; similar in texture to the glumes (membranous or papery); not becoming indurated; entire; pointed; awnless; hairless; non-carinate; having the margins lying flat on the palea; with a clear germination flap; 3 nerved. Palea present; relatively long; 2-nerved (membranous); 2-keeled. Lodicules present (tiny); 2; free; fleshy; glabrous; not or scarcely vascularized. Stamens 3. Anthers penicillate; without an apically prolonged connective. Ovary glabrous. Styles fused. Stigmas 2; red pigmented.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small (3 mm long); compressed dorsiventrally. Hilum short. Embryo large; waisted.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Intercostal zones exhibiting many atypical long-cells. Mid-intercostal long-cells having markedly sinuous walls and having straight or only gently undulating walls (mixed). Microhairs present; panicoid-type; 51–57 microns long; 5.1–5.4 microns wide at the septum. Microhair total length/width at septum 9.4–11.2. Microhair apical cells 25.5–27 microns long. Microhair apical cell/total length ratio 0.45–0.5. Stomata common; 23.5–28–33 microns long. Subsidiaries mostly low dome-shaped (sometimes tending to parallel). Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare. With cushion-based macrohairs. Costal zones with short-cells. Costal short-cells conspicuously in long rows (but rather ambiguous, because the costal short-cells rather long!). Costal silica bodies ‘panicoid-type’; mostly dumb-bell shaped; not sharp-pointed.

Transverse section of leaf blade, physiology. C4; XyMS–. Mesophyll with radiate chlorenchyma. Leaf blade adaxially flat (?). Midrib conspicuous; having a conventional arc of bundles (1 large plus 8 small bundles); with colourless mesophyll adaxially. Bulliforms not present in discrete, regular adaxial groups (constituting most of the epidermis). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders absent. Sclerenchyma all associated with vascular bundles.

Taxonomy. Panicoideae; Panicodae; Paniceae.

Distribution, ecology, phytogeography. 1 species; southern India & Burma, especially coastal. Species of open habitats; halophytic, or glycophytic. Mainly in coastal sand.

Paleotropical. Indomalesian. Indian and Indo-Chinese.

References, etc. Leaf anatomical: this project.

Illustrations. • Abaxial epidermis of leaf blade

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).