The grass genera of the world
Habit, vegetative morphology. Perennial; caespitose. Culms herbaceous; branched above, or unbranched above. The branching simple. Culm nodes hairy, or glabrous. Leaves mostly basal. Leaf blades narrow; without cross venation; persistent. Ligule an unfringed membrane; not truncate.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality.
Inflorescence. Inflorescence a single raceme (spicate, with a winged rachis which partially embraces the spikelets). Inflorescence axes not ending in spikelets (the spikes apparently bare-tipped). Rachides winged (partially embracing the spikelets). Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary, or paired; secund (often in back to back pairs, in one row along the midrib of the rachis); not two-ranked (in one row); pedicellate; consistently in long-and-short combinations (in T. mosquitiensis), or not in distinct long-and-short combinations; in T. mosquitiensis unequally pedicellate in each combination (the upper pedicel here being longer, though partially adnate to the rachis). Pedicels of the pedicellate spikelets (when in unequally-pedicellate pairs) discernible, but fused with the rachis. The shorter spikelets hermaphrodite. The longer spikelets hermaphrodite.
Female-fertile spikelets. Spikelets 2–4 mm long; alternately abaxial and adaxial; compressed laterally, or not noticeably compressed, or compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent (but with a glabrous swelling involving the glume bases, at the base of the spikelet).
Glumes present; two; very unequal; shorter than the adjacent lemmas, or long relative to the adjacent lemmas; dorsiventral to the rachis; hairy (the upper), or hairless; not pointed; awnless (but the upper sometimes mucronate with produced nerves); non-carinate; very dissimilar (the lower minute and scarious, the upper conspicuous but thin). Lower glume 0 nerved. Upper glume 3–7 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. The proximal incomplete florets male. The proximal lemmas furrowed or bifid; awnless (sometimes mucronate); 5–7 nerved; more or less equalling the female-fertile lemmas; similar in texture to the female-fertile lemmas (firm); not becoming indurated (subindurate).
Female-fertile florets 1. Lemmas decidedly firmer than the glumes; striate; becoming indurated (thinly so); entire; pointed; awnless; hairy (on the apical margin only), or hairless; non-carinate; having the margins inrolled against the palea; with a clear germination flap; faintly 3–5 nerved. Palea present; relatively long; textured like the lemma (firm); 2-nerved; 2-keeled. 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 free to their bases. Stigmas 2; red pigmented.
Fruit, embryo and seedling. Fruit free from both lemma and palea; compressed dorsiventrally. Hilum short to long-linear (elongated, up to half the grain length). Embryo large.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present, or absent. Intercostal papillae over-arching the stomata; consisting of one symmetrical projection per cell. Long-cells similar in shape costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls, or having straight or only gently undulating walls. Microhairs present; panicoid-type; (33–)39–66(–69) microns long; (6–)7.5–9.6(–11.4) microns wide at the septum. Microhair total length/width at septum 3.5–4.2 (in T. reticulata), or 7.5–11 (in T. petrosa and T. thrasyoides). Microhair apical cells (19.5–)21–45(–46.5) microns long. Microhair apical cell/total length ratio 0.54–0.73. Stomata common; (24–)26–39(–42) microns long. Subsidiaries triangular, or dome-shaped and triangular (T. reticulata), or parallel-sided, dome-shaped, and triangular (T. petrosa); including both triangular and parallel-sided forms on the same leaf (e.g. T. petrosa), or not including both parallel-sided and triangular forms on the same leaf (e.g. T. reticulata, T. thrasyoides). Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs (e.g. T. thrasyoides), or not paired (T. petrosa). Costal short-cells predominantly paired to neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies present and well developed to absent (a few in T. reticulata and T. thrasyoides, none in T. petrosa); panicoid-type (e.g. in T. reticulata, and reduced forms in T. thrasyoides); not sharp-pointed.
Transverse section of leaf blade, physiology. C4; XyMS. Mesophyll with radiate chlorenchyma. Leaf blade nodular in section to adaxially flat; with the ribs more or less constant in size. Midrib conspicuous; having a conventional arc of bundles (1 large and about 20 small bundles); with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; in simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; forming figures, or nowhere forming figures. Sclerenchyma all associated with vascular bundles.
Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paspaleae; Paspalinae. About 20 species.
Distribution, phytogeography, ecology. Tropical South America, Trinidad.
Helophytic; species of open habitats. Savanna, on wet sands.
Rusts and smuts. Rusts Puccinia. Taxonomically wide-ranging species: Puccinia levis.
References, etc. Morphological/taxonomic: Davidse and Burman 1987. Leaf anatomical: studied by us - T. petrosa (Trin.) Chase, T. reticulata Swallen, T. thrasyoides (Trin.) Chase.
Special comments. Thrasya is not convincingly distinguished from Paspalum. Illustrations. • T. thrasyoides, as T. hirsuta: Kunth (1835). • T. petrosa, as Tylothrasya: Fl. Brasiliensis 2 (1842). • T. petrosa, abaxial epidermis of leaf blade: this project. • T. petrosa, TS leaf blade midrib: 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: 11th December 2017. delta-intkey.com/grass’.