The grass genera of the world
Excluding Monium, Pobeguinea, Anadelphia scyphofera
Habit, vegetative morphology. Annual, or perennial; caespitose (when perennial). Culms 20–200 cm high; herbaceous; branched above, or unbranched above. Culm nodes exposed; glabrous. Culm leaves present. Young shoots intravaginal. Leaves mostly basal, or not basally aggregated; auriculate (or seemingly so, by virtue of the ligule), or non-auriculate. Leaf blades linear; narrow; 0.5–5 mm wide; setaceous (e.g. A. pumila), or not setaceous; flat, or acicular; without cross venation; persistent. Ligule an unfringed membrane (sometimes laterally hardened, the margins auricle-like, when the blade narrow); truncate; about 1 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 (occasionally seemingly all so, by suppression of the pedicelled members), or hermaphrodite and male-only, or hermaphrodite and sterile. The male and female-fertile spikelets mixed in the inflorescence. The spikelets overtly heteromorphic (pedicellate awnless, sessile awned); all in heterogamous combinations. Plants seemingly outbreeding, or inbreeding; seemingly chasmogamous (the racemes usually long-peduncled and exserted from the spatheoles), or exposed-cleistogamous (seemingly, in A. trepidaria, in which the reduced raceme is enclosed in the spatheole, cf. Monium).
Inflorescence. Inflorescence paniculate; open, or contracted; with capillary branchlets; spatheate (and spatheolate); a complex of partial inflorescences and intervening foliar organs. Spikelet-bearing axes racemes (usually), or very much reduced (to one sessile spikelet with one more or less vestigial partner, in A. trepidaria - cf. Monium); the spikelet-bearing axes with 23 spikelet-bearing articles, or with 45 spikelet-bearing articles, or with only one spikelet-bearing article (A. trepidaria); solitary; with very slender rachides; disarticulating; disarticulating at the joints. Articles linear; without a basal callus-knob; not appendaged; disarticulating transversely to disarticulating obliquely (less obviously oblique than in Monium); densely long-hairy, or somewhat hairy, or glabrous. Spikelets solitary (sometimes, at least seemingly, in A. trepidaria), or solitary and paired (the pedicelled members - including their pedicels - often missing, vestigial or much reduced and concealed in the callus hairs, at least in parts of the raceme); not secund; sessile and pedicellate (but the pedicellate members not always conspicuous); consistently in long-and-short combinations (probably usually, if evidence of the pedicelled members is diligently sought), or not in distinct long-and-short combinations (often ostensibly solitary, sometimes genuinely so); when paired, 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-sterile spikelets. The pedicellate spikelets very variable in development and size, those of (e.g.) A. pumila and A. leptocoma larger than their sessile partner; awnless or the upper glume shortly awned. The lemmas awnless.
Female-fertile spikelets. Spikelets 3.5–5 mm long; compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present. Callus usually short; blunt (usually), or pointed.
Glumes two; more or less equal; long relative to the adjacent lemmas; hairy, or hairless; without conspicuous tufts or rows of hairs; awned (G1 bidentate to bi-setaceous at tip, G2 more or less long-awned); more or less carinate (G2), or non-carinate (G1); very dissimilar (both hardened, the G1 dorsally rounded or flattened, acuminate and slightly bicarinate towards the tip, the G2 naviculate and keeled towards the tip, its slender awn sometimes long and twisted around the more substantial one of the lemma). Lower glume not two-keeled (except towards the tip); convex on the back to concave on the back; not pitted; relatively smooth; 5–7 nerved (sometimes obscurely so, the median inconspicuous or absent). Upper glume 3 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; epaleate; sterile. The proximal lemmas awnless (truncate to pointed); 0 nerved, or 2 nerved (palea-like); more or less equalling the female-fertile lemmas to decidedly exceeding the female-fertile lemmas; similar in texture to the female-fertile lemmas (hyaline); not becoming indurated.
Female-fertile florets 1. Lemmas less firm than the glumes (i.e. the wings and lobes of the stipe hyaline); not becoming indurated; incised; 2 lobed; deeply cleft; awned. Awns 1; median; from a sinus; geniculate; hairless; much longer than the body of the lemma (8–50 mm long); entered by one vein. Awn bases twisted; not flattened. Lemmas hairless (sometimes ciliate); non-carinate; without a germination flap; emphatically only 1 nerved. Palea absent. Lodicules present (small); 2; free; fleshy; glabrous; not or scarcely vascularized. Stamens 3. Anthers about 2 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles fused (basally); joined below. Stigmas 2.
Fruit, embryo and seedling. Fruit compressed dorsiventrally (somewhat, at least in A. bigeniculata), or not noticeably compressed; glabrous. Hilum short. Embryo large.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present, or absent (A. pumila); intercostal. Intercostal papillae over-arching the stomata to not over-arching the stomata; consisting of one oblique swelling per cell, or consisting of one symmetrical projection per cell (large, fairly thick walled, surface-ornamented in A. leptocoma). Long-cells markedly different in shape costally and intercostally (the costals narrower and more regularly rectangular); of similar wall thickness costally and intercostally (fairly thin walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls (A. pumila), or having straight or only gently undulating walls, or having markedly sinuous walls and having straight or only gently undulating walls (then sinuous only adjoining the costae). Microhairs present; elongated; clearly two-celled; panicoid-type; 33–45 microns long; 6–6.3 microns wide at the septum. Microhair total length/width at septum 5.5–7.1. Microhair apical cells 20–30 microns long. Microhair apical cell/total length ratio 0.59–0.67. Stomata common; 21–29 microns long. Subsidiaries non-papillate; variously dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common (A. pumila), or absent or very rare; of A. pumila in cork/silica-cell pairs and not paired. Costal short-cells conspicuously in long rows. Costal silica bodies present and well developed; panicoid-type; dumb-bell shaped.
Transverse section of leaf blade, physiology. C4; XyMS (but the presumed PCR sheath very thick walled and mestome-sheath like in A. pumila and A. bigeniculata). Mesophyll traversed by columns of colourless mesophyll cells (A. leptocoma), or not traversed by colourless columns. Leaf blade nodular in section. Midrib conspicuous; with one bundle only to having a conventional arc of bundles (A. bigeniculata), or having a conventional arc of bundles; with colourless mesophyll adaxially (this represented by only a few cells in A. bigeniculata). The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups (A. leptocoma), or not present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans (these linked with the traversing colourless columns, in A. leptocoma); associating with colourless mesophyll cells to form arches over small vascular bundles (seemingly, e.g. in A. bigeniculata), or nowhere involved in bulliform-plus-colourless mesophyll arches. Many of the smallest vascular bundles unaccompanied by sclerenchyma, or all the vascular bundles accompanied by sclerenchyma (A. leptocoma). Combined sclerenchyma girders present; forming figures, or nowhere forming figures. Sclerenchyma all associated with vascular bundles.
Cytology. 2n = 20.
Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Anthistiriinae. 13 species.
Distribution, phytogeography, ecology. Tropical Africa.
Savanna, often on shallow soils.
References, etc. Leaf anatomical: studied by us - A. bigeniculata W.D. Clayton, A. leptocoma Pilger, A. pumila Jac.-Fél., A. trepidaria (Stapf) Stapf.
Special comments. Contrast the treatments of Jacques-Félix 1962 and Clayton 1966: an effective resolution of generic limits (involving Anadelphia, Monium and Pobeguinea) awaits acqisition and proper analysis of dependable comparative data - meanwhile, the present descriptions are based on the incomplete sample examined (see the accompanying file). Illustrations. • A. leptocoma (as A. longifolia): Jacques-Félix, 1962. • A. afzeliana, as A. arrecta: Hook. Ic. Pl. 31 (1922)
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’.