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The grass genera of the world

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

Themeda Forssk.

From Arabic thaemed (a small quantity of water preserved in a ditch against a time of need) - the allusion obscure.

Including Androscepia Brong., Anthistiria L. f., Aristaria Jungh., Heterelytron Jungh., Perobachne Presl

Habit, vegetative morphology. Annual, or perennial; caespitose (coarse, very rarely stoloniferous). Culms 30–310 cm high; herbaceous; amply branched above, or unbranched above. The branching simple. Culm nodes hairy, or glabrous. Culm internodes solid, or hollow. Leaves not basally aggregated; non-auriculate. Leaf blades linear; narrow; flat, or folded; not pseudopetiolate; without cross venation; persistent; rolled in bud, or once-folded in bud. Ligule an unfringed membrane to a fringed membrane. 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 male-only, or hermaphrodite and sterile; overtly heteromorphic; in both homogamous and heterogamous combinations (the lower pairs homogamous, homomorphic, forming an involucre under the terminal triad). Apomictic, or reproducing sexually.

Inflorescence. Inflorescence paniculate (leafy, comprising short racemes in spatheate, hard-to-interpret clusters); open; spatheate; a complex of ‘partial inflorescences’ and intervening foliar organs (composed of short racemes in spatheate clusters: each cluster terminated by 1–3 pairs of spikelets, one of each pair sessile and bisexual, the other pedicelled and male-or-sterile (or a triplet of 1 terminal sessile spikelet with 2 pedicellate ones), the whole surrounded by a whorl of 4 male or sterile, sessile spikelets constituting an involucre). Spikelet-bearing axes very much reduced; clustered (the racemes solitary in their spatheoles, these units in groups of three or more in short capituliform glomerules); disarticulating; disarticulating at the joints (each raceme disarticulating at the level of the female-fertile spikelets). Spikelets associated with bractiform involucres (constituted by the four imperfect spikelets). The involucres persistent on the rachis. Spikelets paired and in triplets; the clusters secund, or not secund; sessile and pedicellate; consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets free of the rachis. The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets male-only, or sterile.

Female-fertile spikelets. Spikelets not noticeably compressed to compressed dorsiventrally; falling with the glumes (the clusters disarticulating immediately above the involucres). Rachilla terminated by a female-fertile floret. Hairy callus present (usually acute to pungent). Callus pointed.

Glumes two; more or less equal; long relative to the adjacent lemmas; awnless; with the keel conspicuously winged, or without a median keel-wing; leathery. Lower glume not two-keeled; convex on the back; not pitted; relatively smooth; 7–11 nerved. Upper glume 1–5 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. The proximal incomplete florets 1; epaleate; sterile. The proximal lemmas awnless; 0 nerved; similar in texture to the female-fertile lemmas (hyaline); not becoming indurated.

Female-fertile florets 1. Lemmas hyaline, stipitate beneath the awn; less firm than the glumes; not becoming indurated; usually entire; not deeply cleft; awned. Awns 1; median; usually apical; geniculate; hairy; much shorter than the body of the lemma to much longer than the body of the lemma. Lemmas hairless; non-carinate; 1 nerved. Palea present, or absent; when present, conspicuous but relatively short, or very reduced; not indurated (hyaline); nerveless. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2; red pigmented.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small; longitudinally grooved (channelled down one side); compressed dorsiventrally. Hilum short. Embryo large. Endosperm hard; without lipid; containing compound starch grains. Embryo without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.

Seedling with a long mesocotyl. First seedling leaf with a well-developed lamina. The lamina broad; curved; 21–30 veined.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present. Intercostal papillae over-arching the stomata; several per cell (finger-like projections). Long-cells similar in shape costally and intercostally; differing markedly in wall thickness costally and intercostally (the costals thicker-walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; (26–)38–64(–72) microns long; 4.2–6.6 microns wide at the septum. Microhair total length/width at septum 7.8–14.3. Microhair apical cells (10–)13–19.5(–22.5) microns long. Microhair apical cell/total length ratio 0.35–0.44. Stomata common; 24–30 microns long. Subsidiaries papillate; low dome-shaped and triangular, or triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common, or absent or very rare; in cork/silica-cell pairs and not paired; silicified (rarely), or not silicified. Intercostal silica bodies tall-and-narrow, or vertically elongated-nodular, or cross-shaped. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; cross shaped to dumb-bell shaped, or nodular; not sharp-pointed.

Transverse section of leaf blade, physiology. C4; XyMS–. PCR sheath outlines uneven. PCR cell chloroplasts with reduced grana; centrifugal/peripheral. Mesophyll with radiate chlorenchyma. Leaf blade ‘nodular’ in section, or adaxially flat; with the ribs more or less constant in size. Midrib conspicuous; with one bundle only, or having a conventional arc of bundles. Bulliforms not present in discrete, regular adaxial groups (constituting most of the epidermis, irregular save for a large fan over the keel). 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.

Culm anatomy. Culm internode bundles in one or two rings.

Phytochemistry. Tissues of the culm bases with abundant starch. Leaves without flavonoid sulphates (1 species).

Cytology. Chromosome base number, x = 5 and 10. 2n = 20, 40, 60, and 80 (and aneuploids).

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Anthistiriinae. 18 species.

Distribution, phytogeography, ecology. Warm Africa, Asia, Australia.

Commonly adventive. Mesophytic; species of open habitats; glycophytic. Savanna.

Economic aspects. Significant weed species: T. arguens, T. villosa. Important native pasture species: T. anathera, T. australis, T. cymbaria, T. triandra.

Rusts and smuts. Rusts — Phakopsora and Puccinia. Taxonomically wide-ranging species: Phakopsora incompleta, Puccinia versicolor, and ‘Uromycesclignyi. Smuts from Ustilaginaceae. Ustilaginaceae — Sorosporium, Sphacelotheca, Tolyposporium, and Ustilago.

References, etc. Leaf anatomical: Metcalfe 1960; studied by us - T. australis (R. Br.) Stapf.

Illustrations. • T. triandra: Gardner, 1952. • General aspect (T. triandra): Gibbs Russell et al., 1990. • Spikelet cluster of T. triandra. • Spikelet cluster detail of T. triandra. • Themeda triandra (as Anthistiria): Hooker, Fl. Tasmaniae (1860). • T. arundinacea, as Anthistiria: Kunth (1835). • T. triandra, abaxial epidermis of leaf blade: this project. • T. triandra, abaxial epidermis of leaf blade: this project. • Pollen antigens: Watson and Knox (1976)

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.’.