The grass genera of the world
Habit, vegetative morphology. Perennial; caespitose (with densely villous cataphylls). Culms 40–100 cm high; herbaceous; unbranched above. Culm nodes hairy. Young shoots intravaginal. Leaves not basally aggregated; non-auriculate. Leaf blades linear-lanceolate (acuminate, those of the upper leaves reduced); narrow; 2–4 mm wide; flat, or rolled; without cross venation; persistent. Ligule a fringe of hairs; 0.3–0.4 mm long.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality.
Inflorescence. Inflorescence paniculate; open (pyramidal, many-flowered); with capillary branchlets; espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate (the pedicels flexuous). Pedicel apices oblique.
Female-fertile spikelets. Spikelets 4–4.5 mm long (silvery-villous); compressed dorsiventrally; falling with the glumes; with a distinctly elongated rachilla internode between the glumes and with distinctly elongated rachilla internodes between the florets. The upper floret not stipitate (at least, not like Ichnanthus). Rachilla terminated by a female-fertile floret. Hairy callus present (via the falcate pedicel tip). Callus short.
Glumes present; two; very unequal; (the upper) long relative to the adjacent lemmas; hairy (silvery-villous); without conspicuous tufts or rows of hairs; pointed (acute); awnless; non-carinate; similar. Lower glume longer than half length of lowest lemma; 3–5 nerved. Upper glume 5–7 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 (two winged, hyaline); not becoming conspicuously hardened and enlarged laterally. The proximal incomplete florets male, or sterile. The proximal lemmas awnless; 5–7 nerved; more or less equalling the female-fertile lemmas to decidedly exceeding the female-fertile lemmas; less firm than the female-fertile lemmas (herbaceous, hairy, similar to the glumes); not becoming indurated.
Female-fertile florets 1. Lemmas ellipsoid; decidedly firmer than the glumes; smooth (shining, pale); becoming indurated; entire; pointed, or blunt; awnless; hairless; glabrous; non-carinate; having the margins inrolled against the palea; with a clear germination flap (?). Palea present; relatively long; entire; awnless, without apical setae; textured like the lemma; indurated; 2-nerved; keel-less. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers 1–1.4 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Stigmas 2.
Fruit, embryo and seedling. Fruit small (2.2 mm long); longitudinally grooved; compressed dorsiventrally. Hilum long-linear. Embryo large.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals more regularly rectangular); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular (though mostly somewhat narrowed at the ends); having markedly sinuous walls. Microhairs present (and abundant); of peculiar form, not reliably interpretable in surface view: the apical cell relatively thick walled and darkly pigmented, usually more or less bent over and often pyriform, the basal cell apparently more or less sunken. Stomata common; 48–51 microns long. Subsidiaries low dome-shaped (mostly), or triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies crescentic and oryzoid-type. Costal short-cells predominantly paired. Costal silica bodies rounded, or tall-and-narrow (common), or crescentic (commonly broadly D-shaped); not sharp-pointed.
Transverse section of leaf blade, physiology. C4. The anatomical organization somewhat unconventional (in exhibiting numerous small, peculiarly positioned vascular bundles). XyMS+. PCR sheath outlines even. PCR sheath extensions absent. Mesophyll without adaxial palisade. Leaf blade nodular in section (peculiarly so: each half-blade with flat bottomed abaxial ribs corresponding with each main bundle, the adaxial surface with a wide, triangular marginal rib and internal to it one broad rib incorporating two costal zones and the intercostal region between them). Midrib and blade having complex vascularization (there being numerous small bundles, including some aligned vertically adjoining the abaxial girders of the primary bundles, and some occurring adaxially to the two primaries which are incorporated in the blade margin). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; forming figures (all the primaries having a short adaxial girder and an elongated abaxial one, the combination constituting a massive I). Sclerenchyma all associated with vascular bundles.
Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae (probably). Soreng et al. (2015): Panicoideae; Panicodae; Paspaleae; Arthropogoninae. 1 species (T. arnactites).
Distribution, phytogeography, ecology. Brazil.
Species of open habitats. Savanna.
References, etc. Leaf anatomical: studied by us, and described here from poorly preserved material, with a disintegrating midrib which could not be observed. The peculiar vascular bundle pattern and the unusual microhairs need further, detailed study.
Illustrations. • T. arnactites, abaxial epidermis of 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: 11th December 2017. delta-intkey.com/grass’.