| | The grass genera of the world |
From the Greek opsis (appearance) and Danthonia (another grass genus, q.v.), alluding to likeness.
Including Gazachloa Phipps, Jacquesfelixia Phipps, Petrina Phipps, Pleioneura (C. E. Hubb.) Phipps, Rattraya Phipps, Xerodanthia Phipps
Habit, vegetative morphology. Annual (rarely), or perennial; caespitose (sometimes densely so). Culms 25–200 cm high; herbaceous; sparsely branched above, or unbranched above. The branching simple. Culm nodes hairy, or glabrous. Culm internodes solid, or hollow. Plants unarmed. Young shoots intravaginal. Leaves not basally aggregated; non-auriculate. Leaf blades linear to lanceolate; broad, or narrow; 1.5–18 mm wide; flat, or rolled (but only slightly so); pseudopetiolate (D. petiolata), or not pseudopetiolate; without cross venation; persistent. Ligule a fringe of hairs; 0.5–2.5 mm long. Contra-ligule present (as an irregular line of hairs), or absent (rarely).
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence paniculate (the spikelets in twos and threes); open, or contracted; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets in triplets (rarely), or paired; not secund; pedicellate.
Female-fertile spikelets. Spikelets 5–20 mm long; purplish; compressed laterally; disarticulating above the glumes; disarticulating between the florets; with conventional internode spacings. Rachilla terminated by a female-fertile floret; hairy. Hairy callus present. Callus short; blunt (bidentate in D. barbata).
Glumes two; very unequal; (the longer) long relative to the adjacent lemmas; hairless; nearly always glabrous; awnless, or awned (G2 sometimes aristate); non-carinate (abaxially rounded); very dissimilar (G1 acute to acuminate, G2 with the tip extended). Lower glume shorter than the lowest lemma; 3–5 nerved. Upper glume 3–5 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 (membranous between its two narrowly winged keels). The proximal incomplete florets male. The proximal lemmas awnless; (3–)5–9 nerved.
Female-fertile florets 1. Lemmas usually but not always with 2–8 transverse rows of hairs or tufts; similar in texture to the glumes (to slightly firmer); incised; 2 lobed; deeply cleft; awned. Awns 1 (usually), or 3; median, or median and lateral (D. chimanimaniensis); the median different in form from the laterals (when laterals present); from a sinus; geniculate; hairless (scabrous); much longer than the body of the lemma; entered by several veins; deciduous. The lateral awns when present, shorter than the median (in the form of short, scaberulous bristles). Awn bases twisted; flattened. Lemmas hairy (usually), or hairless (sometimes glabrous). The hairs in tufts, or not in tufts; in transverse rows, or not in transverse rows (in Sect. Pleioneura). Lemmas non-carinate; having the margins inrolled against the palea; with a clear germination flap (this just above the callus, often hidden by hairs); 7–9 nerved; with the nerves non-confluent. Palea present; relatively long (about equalling the lemma); apically notched; awnless, without apical setae; textured like the lemma; not indurated; 2-nerved; 2-keeled. Palea keels winged (the wings clasped by the inrolled lemma margins, often terminating in a clavate swelling or auricle); glabrous, or scabrous. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers 1.7–4 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2; white, or red pigmented (purple).
Fruit, embryo and seedling. Hilum long-linear. Embryo large.
Seedling with a loose coleoptile. First seedling leaf with a well-developed lamina. The lamina broad; curved.
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 (the costals narrower); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls, or having straight or only gently undulating walls (the sinuosity sporadically apparent only at the outermost optical section, in D. occidentalis). Microhairs present; elongated; clearly two-celled; panicoid-type; 57–60 microns long; 6–7.5 microns wide at the septum. Microhair total length/width at septum 8–10. Microhair apical cells 24–30 microns long. Microhair apical cell/total length ratio 0.4–0.5. Stomata common; 30–34.5 microns long. Subsidiaries non-papillate; low to medium dome-shaped and triangular (in D. occidentalis, mostly with a small point). Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies in D. occidentalis, nearly all crescentic and oryzoid-type (small and irregularly shaped, but mostly more or less crescentic). Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; cross shaped (bordering the costal zones, in D. occidentalis), or dumb-bell shaped.
Transverse section of leaf blade, physiology. C4. The anatomical organization conventional (usually), or unconventional. Organization of PCR tissue when unconventional, Arundinella type. XyMS+ (in D. occidentalis, the mestome sheath 2–3 cells wide at the XyMs position), or XyMS–. PCR sheath outlines even. PCR cell chloroplasts centrifugal/peripheral. Mesophyll with radiate chlorenchyma; without adaxial palisade; exhibiting ‘circular cells’ (?), or without ‘circular cells’ (D. barbata, D. dinteri, D. occidentalis, D. pruinosa); not traversed by colourless columns. Leaf blade ‘nodular’ in section (slightly), or adaxially flat (usually more conspicuously ribbed abaxially). Midrib conspicuous, or not readily distinguishable; with one bundle only, or having a conventional arc of bundles; with colourless mesophyll adaxially, or without colourless mesophyll adaxially (D. occidentalis with an adaxial mass of colourless cells between each pair of major bundles, over each of the intervening small bundles). Bulliforms present in discrete, regular adaxial groups (the groups large); in simple fans, or associated with colourless mesophyll cells to form deeply-penetrating fans; associating with colourless mesophyll cells to form arches over small vascular bundles (in D. occidentalis), or nowhere involved in bulliform-plus-colourless mesophyll arches. Many of the smallest vascular bundles unaccompanied by sclerenchyma (all of them, in D. occidentalis), or all the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with all the large bundles, in D. occidentalis), or absent; in D. occidentalis forming ‘figures’ (forming T’s, in places). Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 9, or 12 (?). 2n = 18, 24, and 36. 2 and 4 ploid.
Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Arundinelleae. Soreng et al. (2015): Panicoideae; Tristachyideae. About 20 species.
Distribution, phytogeography, ecology. Africa, Arabia.
Commonly adventive. Mesophytic to xerophytic; species of open habitats; glycophytic. Savanna woodland and desert fringes.
Rusts and smuts. Rusts — Puccinia.
References, etc. Morphological/taxonomic: Phipps 1967. Leaf anatomical: Metcalfe 1960; studied by us - D. barbata (Nees) C.E. Hubb., D. occidentalis Jac.-Fél.; photos of D. dinteri and D. pruinosa provided by R.P. Ellis.
Illustrations. • Danthoniopsis viridis, as D. gossweileri: Hook. Ic. Pl. 31 (1916). • D. dinteri: Gibbs Russell et al., 1990. • Spikelet of Danthoniopsis occidentalis. • Disarticulated spikelet of Danthoniopsis occidentalis.
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: 25th January 2024. delta-intkey.com’.
