The grass genera of the world
Type species: Type: U. truncatum (Maiden & Betche) Stapf.
Habit, vegetative morphology. Annual (or short-lived perennial); caespitose. Culms 15–50 cm high; herbaceous; flattened; branched above. Culm nodes hairy. Culm leaf sheaths rounded. Culm internodes hollow. Leaves not basally aggregated; non-auriculate. Leaf blades linear; narrow; about 4 mm wide; flat (soft); not pseudopetiolate; without cross venation; persistent. Ligule a fringed membrane to a fringe of hairs; 0.75–1.5 mm long.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence of spicate main branches (of short spikes, each of 2–4 spikelets, the spikes on a common, flattened cartilaginous axis); contracted. Primary inflorescence branches borne distichously. Inflorescence with axes ending in spikelets (but these rudimentary), or axes not ending in spikelets (often ending in a flattened bristle). Rachides flattened (i.e., the common axis). Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes disarticulating; falling entire (the short spikes falling with the adjacent internode of the fragile common axis). Spikelets solitary; not secund; sessile. Pedicel apices discoid.
Female-fertile spikelets. Spikelets 8–10 mm long; lanceolate; compressed dorsiventrally; falling with the glumes (and with the spike). Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension naked. Hairy callus absent.
Glumes two; relatively large; very unequal; shorter than the adjacent lemmas (the upper 1/2, the lower 1/4 its length); hairless; glabrous; not pointed; awnless; similar (firmly chartaceous, truncate). Lower glume 3–7 nerved. Upper glume distinctly saccate (gibbous); 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 (2-keeled). The proximal incomplete florets sterile. The proximal lemmas membranous along the midline, leathery on the sides, caudate-acuminate; awnless (but caudate-acuminate); 3–5 nerved; not becoming indurated (but cartilaginous between the outer nerves).
Female-fertile florets 1. Lemmas ovate-elliptic, subulate-caudate above; decidedly firmer than the glumes; smooth; becoming indurated (thinly); yellow in fruit; entire; pointed; awned. Awns 1; median; apical; non-geniculate. Lemmas hairless; non-carinate; having the margins lying flat on the palea; 5 nerved. Palea present; entire (apically prolonged, the tip caudate); with apical setae; textured like the lemma; indurated; 2-nerved. Lodicules present; 2; fleshy. Stamens 3. Anthers about 0.5 mm long. Ovary apically glabrous. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit small. Hilum short. Embryo large.
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; (66–)69–75(–81) microns long; 6–7.5 microns wide at the septum. Microhair total length/width at septum 9.2–11.9. Microhair apical cells (30–)33–42(–43.5) microns long. Microhair apical cell/total length ratio 0.43–0.57. Stomata common; 34.5–36 microns long. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies mainly cross-shaped. Prickles abundant. Costal zones with short-cells. Costal short-cells conspicuously in long rows. Costal silica bodies panicoid-type; not sharp-pointed.
Transverse section of leaf blade, physiology. C4; XyMS. Mesophyll with radiate chlorenchyma. Leaf blade adaxially with numerous large, thin walled, blunt macrohairs; with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only. Bulliforms not present in discrete, regular adaxial groups (the epidermis extensively, irregularly bulliform). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders absent (the large bundles with heavy strands simulate combined girders in collapsed material, but there always appear to be thin walled, colourless cells intevening between the PCR sheath and the fibre groups). Sclerenchyma all associated with vascular bundles.
Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Cenchrinae. 1 species (U. truncatum).
Distribution, phytogeography, ecology. Australia.
Xerophytic; species of open habitats. Grassland on clay.
References, etc. Leaf anatomical: studied by us.
Illustrations. • U. truncatum: Hook. Ic. Pl. 31 (1916). • U. truncatum: Lazarides (1981). • U. truncatum, abaxial epidermis of leaf blade: this project. • U. truncatum, 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’.