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The grass genera of the world

L. Watson, T.D. Macfarlane, and M.J. Dallwitz

Urochlaena Nees

~ Tribolium

Type species: U. pusilla Nees.

Habit, vegetative morphology. Annual; caespitose. Culms 7–20 cm high; herbaceous (glabrous); much branched from the base. Culm nodes glabrous. Culm internodes hollow. Plants unarmed. Young shoots intravaginal. Leaves not basally aggregated; non-auriculate; without auricular setae (but hair-tufted at the mouth of the sheath). The uppermost sheath blade-bearing, broadly winged from the margins in the upper half and clasping the inflorescence. Leaf blades linear; narrow; 0.5–2 mm wide (to 3 cm long); flat, or rolled; without cross venation; persistent. Ligule a fringed membrane; not truncate (acute); 0.5 mm long. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite and sterile; overtly heteromorphic (those at the bases of the lower branches 1-flowered, or consisting of 2–4 empty glumes).

Inflorescence. Inflorescence paniculate; deciduous in its entirety (the culm disarticulating at the uppermost node, complete with the inflorescence and the uppermost leaf); contracted (to 2.5 cm long); more or less ovoid (small, embraced at the base by the sheath of the uppermost leaf and deciduous with it); not comprising ‘partial inflorescences’ and foliar organs. Spikelets solitary; not secund.

Female-fertile spikelets. Spikelets 4 mm long; slightly compressed laterally; falling with the glumes (and with the whole inflorescence, the adjacent node and its leaf); with conventional internode spacings. Rachilla prolonged beyond the uppermost female-fertile floret; hairy; the rachilla extension with incomplete florets. Callus absent.

Glumes two; relatively large; more or less equal; shorter than the spikelets; hairy (at least, the upper margins with tubercle based hairs); pointed; awned (acuminate into scabrid 8–13 mm awns); non-carinate (dorsally rounded); similar (ovate-oblong, acuminate, membranous). Lower glume shorter than the lowest lemma; 4–6 nerved. Upper glume 5–7 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped; awned.

Female-fertile florets 3–7. Lemmas similar in texture to the glumes; not becoming indurated; entire; pointed; awned (tapering into the awn). Awns 1; median; apical; non-geniculate; recurving; much shorter than the body of the lemma to much longer than the body of the lemma (but shorter than the glume awns); entered by several veins. Lemmas hairy (with fine tubercle-based marginal hairs above, and club-shaped hairs on the mid-nerve); non-carinate (somewhat rounded on the back); without a germination flap; 7–9 nerved; with the nerves confluent towards the tip. Palea present (linear-oblong); relatively long (equalling the lemma); apically notched; awnless, without apical setae; thinner than the lemma (membranous); not indurated; 2-nerved; 2-keeled. Palea keels wingless; hairy. Lodicules present (minute); 2; fleshy; glabrous. Stamens 3. Anthers about 3 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases (short). Stigmas 2; white.

Fruit, embryo and seedling. Fruit free from both lemma and palea (enclosed by little-altered lemma and palea); small (1–2 mm long); compressed dorsiventrally (and obscurely concave on the front). Hilum short (but relatively large). Pericarp free. Embryo large; without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins meeting.

Ovule, embryology. Micropyle not noticeably oblique. Outer integument covering no more than the chalazal half of the ovule; two cells thick at the micropylar margin. Inner integument discontinuous distally; not thickened around the micropyle. Synergids haustorial; exhibiting large, globular starch grains.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally to markedly different in shape costally and intercostally (the costals narrower); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type. Stomata common. Subsidiaries dome-shaped (mainly), or triangular. Intercostal short-cells common. Costal zones with short-cells. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; small, dumb-bell shaped and nodular; not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with radiate chlorenchyma (somewhat so); without adaxial palisade; tending to Isachne-type (loose). Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size (low, round-topped). Midrib not readily distinguishable; with one bundle only. Bulliforms not present in discrete, regular adaxial groups (the bulliforms in conspicuously irregular groups). Combined sclerenchyma girders absent. Sclerenchyma all associated with vascular bundles.

Cytology. Chromosome base number, x = 7.

Classification. Watson & Dallwitz (1994): Arundinoideae; Danthonieae (?). Soreng et al. (2015): Danthonioideae (as a synonym); Danthonieae. 1 species (U. pusilla).

Distribution, phytogeography, ecology. South Africa.

Xerophytic; species of open habitats; glycophytic. In Karoo.

References, etc. Leaf anatomical: photos provided by R.P. Ellis.

Illustrations. • U. pusilla: Hook. Ic. Pl. 14 (1881). • Inflorescence of U. pusilla: Gibbs Russell et al., 1990

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.’.