Tribolium Desv.
From the Latin tria (three) and bolus (a fiery meteor in the form of an arrow), possibly referring to three florets encased in the very bristly glumes.
Including Brizopyrum Stapf, Lasiochloa Kunth, Plagiochloa Adamson and Sprague, Urochlaena Nees
Habit, vegetative morphology. Annual, or perennial; rhizomatous, or stoloniferous, or caespitose (mostly). Culms 2–60 cm high; herbaceous; branched above, or unbranched above. Culm nodes glabrous. Culm internodes hollow. Plants unarmed. Young shoots extravaginal (in T. uniolae), or intravaginal (the rest). Leaves mostly basal, or not basally aggregated; non-auriculate; without auricular setae (but sometimes hair-tufted at the mouth of the sheath). The uppermost sheath sometimes (Urochlaena) blade-bearing, broadly winged from the margins in the upper half and clasping the inflorescence. Leaf blades linear; narrow; 0.3–4 mm wide; setaceous, or not setaceous; flat, or rolled; without abaxial multicellular glands; without cross venation; persistent; a fringed membrane, or a fringed membrane to a fringe of hairs; 0.3–2 mm long (the fringe sometimes double, the row of short hairs interspersed with longer ones). Contra-ligule absent.
Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant (in Urochlaena, and sometimes in T. uniolae), or all alike in sexuality; hermaphrodite and sterile (Urochlaena, T. uniolae), or hermaphrodite; overtly heteromorphic (in Urochlaena, those at the bases of the lower branches 1-flowered, or consisting of 2–4 empty glumes), or homomorphic.
Inflorescence. Inflorescence few spikeleted to many spikeleted; a single spike (in T. uniolae, this distichous), or a single raceme (occasionally), or paniculate (generally, and compact, with short pedicels and branches); deciduous in its entirety (in Urochlaena, where the culm disarticulates at the uppermost node, complete with the inflorescence and the uppermost leaf), or not deciduous; contracted; capitate, or more or less ovoid, or spicate (sometimes interrupted); espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; secund, or not secund; biseriate, or distichous (T. uniolae), or not two-ranked; very shortly pedicellate, or subsessile, or sessile; imbricate.
Female-fertile spikelets. Spikelets 2–10 mm long; broadly cuneate, or suborbicular; compressed laterally, or not noticeably compressed; falling with the glumes (and with the whole inflorescence, the adjacent node and its leaf (Urochlaena)), or disarticulating above the glumes (in the rest); tardily disarticulating between the florets; with conventional internode spacings. Rachilla prolonged beyond the uppermost female-fertile floret; hairy, or hairless; the rachilla extension with incomplete florets. Hairy callus absent. Callus absent, or short (glabrous).
Glumes two; very unequal to more or less equal; shorter than the spikelets to exceeding the spikelets; shorter than the adjacent lemmas, or long relative to the adjacent lemmas; dorsiventral to the rachis (when orientation ascertainable); hairy (usually, with glandular, often tubercle-based hairs), or hairless; glabrous, or scabrous; pointed (acute, acuminate or subulate-caudate); awned (the awns to 13 mm in Urochlaaena), or awnless; carinate, or non-carinate; similar (naviculate, membranous to chartaceous). Lower glume shorter than the lowest lemma to much exceeding the lowest lemma; (3–)5(–7) 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 (Urochlaena), or awnless. Spikelets without proximal incomplete florets.
Female-fertile florets 2–9(–14). Lemmas less firm than the glumes to similar in texture to the glumes (membranous to chartaceous); not becoming indurated; entire (sometimes emarginate, scarcely incised); pointed to blunt (acute to emarginate); not deeply cleft; awnless to mucronate (sometimes with minute terminal or lateral awns), or awned (in Urochlaena, tapering into the awn). Awns in Urochlaena, 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 (usually with clavate hairs), or hairless; carinate (usually), or non-carinate (sometimes); without a germination flap; (5–)7 nerved, or 9 nerved; with the nerves confluent towards the tip. Palea present; relatively long; apically notched; awnless, without apical setae; thinner than the lemma; not indurated (membranous); 2-nerved; 2-keeled. Palea keels winged, or wingless; scabrous, or hairy. Lodicules present; 2; free; fleshy; ciliate, or glabrous; heavily vascularized, or not or scarcely vascularized. Stamens 3. Anthers 1–3 mm long; not penicillate; without an apically prolonged connective. Ovary glabrous. Styles free to their bases. Stigmas 2; white, or brown.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small (1–2 mm long); yellow-brown; obovate; compressed dorsiventrally. Hilum short. Pericarp fairly loosely adherent, or free (Urochlaena). Embryo large (Urochlaena), or small; waisted; 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 (Urochlaena pusilla); more than two cells thick at the micropylar margin (T. obliterum), or two cells thick at the micropylar margin (Urochlaena pusilla). Inner integument discontinuous distally; not thickened around the micropyle. Synergids haustorial (strongly developed); exhibiting large, globular starch grains.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally, or markedly different in shape costally and intercostally (when the costals are much narrower); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular to fusiform; having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; panicoid-type. Microhair apical cell wall thinner than that of the basal cell and often collapsed. Microhairs (58.5–)64–84(–99) microns long. Microhair basal cells 30–36 microns long. Microhairs 9.6–16.5 microns wide at the septum. Microhair total length/width at septum 3.8–8.3. Microhair apical cells (30–)34–50(–60) microns long. Microhair apical cell/total length ratio 0.48–0.66. Stomata absent or very rare, or common; 21–33 microns long. Subsidiaries high dome-shaped, or dome-shaped and triangular. Guard-cells overlapped by the interstomatals (slightly), or overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs (but often apparently solitary, through overlapping); silicified. Intercostal silica bodies present and perfectly developed. Costal zones with short-cells. Costal short-cells conspicuously in long rows. Costal silica bodies present throughout the costal zones; rounded (few), or ‘panicoid-type’; predominantly cross shaped and dumb-bell shaped (short), or dumb-bell shaped and nodular; not sharp-pointed.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C3; XyMS+. Mesophyll with radiate chlorenchyma (somewhat so, in Urochlaena), or with non-radiate chlorenchyma (the chlorenchyma closely packed); without adaxial palisade; tending to Isachne-type (loose, in Urochlaena), or not Isachne-type. Leaf blade with distinct, prominent adaxial ribs to adaxially flat; with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups, or not present in discrete, regular adaxial groups (in Urochlaena, the bulliforms in conspicuously irregular groups); in simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma, or all the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present, or absent (but then with strong adaxial and abaxial strands); forming ‘figures’ (most major bundles with narrow I’s). Sclerenchyma all associated with vascular bundles, or not all bundle-associated. The ‘extra’ sclerenchyma in abaxial groups. The lamina margins with fibres.
Phytochemistry. Tissues of the culm bases with abundant starch, or with little or no starch.
Cytology. Chromosome base number, x = 6, or 7 (Urochlaena). 2n = 12. 2–6 ploid.
Taxonomy. Arundinoideae; Danthonieae.
Distribution, ecology, phytogeography. 10 species; South Africa. Commonly adventive. Mesophytic to xerophytic (winter rainfall); species of open habitats; glycophytic. Fynbos and Karoo.
Paleotropical and Cape. African. Namib-Karoo and Ascension and St. Helena.
Rusts and smuts. Smuts from Ustilaginaceae. Ustilaginaceae — Ustilago.
References, etc. Morphological/taxonomic: Renvoize 1985(c); Linder and Davidse 1997. Leaf anatomical: this project; photos of Urochlaena pusilla provided by R.P. Ellis.
Special comments. Linder and Davidse (1997) include the very aberrant T. pusillum here on cladistic grounds; arguing that because its numerous characteristics are interpreted as unique autapomorphies, recognition of the monotypic genus Urochlaena renders Tribolium paraphyletic. Such rather startling applications of cladistic theory are at odds with the practical requirement that taxonomic systems should facilitate making generalisations; and in view of the well known difficulties regarding extent of sampling and interpretations of morphological characters and character states, and taxonomic sampling limitations (notably, lack of information on extinct forms), corrobarative evidence from nucleic acid sequencing seems essential. In this instance, the latter may exist, but seemingly remains unpublished.
Illustrations. • General aspect. • Inflorescence. • Transverse section 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.’ http://biodiversity.uno.edu/delta/. 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).
