| | The grass genera of the world |
From the Greek dicha (two, asunder) and anthos (flower), alluding to two kinds of spikelet (male-only or neuter, versus hermaphrodite) found in different parts of an inflorescence.
Bluegrasses.
Including Diplasanthum Desv., Lepeocercis Trin.
Excluding Bothriochloa, Eremopogon
Habit, vegetative morphology. Annual (rarely), or perennial; rhizomatous, or stoloniferous, or caespitose, or decumbent. Culms 15–200 cm high; herbaceous; branched above, or unbranched above. The branching simple. Culm nodes hairy, or glabrous. Culm internodes solid. The shoots aromatic, or not aromatic. Leaves not basally aggregated; non-auriculate. Leaf blades narrow; not cordate, not sagittate; flat; without cross venation; persistent; rolled in bud. Ligule present; an unfringed membrane to a fringed membrane.
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 (the pedicellate spikelets smaller, awnless), or homomorphic; in both homogamous and heterogamous combinations (the lowest pair being imperfect and homogamous). Plants exposed-cleistogamous, or chasmogamous.
Inflorescence. Inflorescence of spicate main branches (many-jointed ‘racemes’), or paniculate (the lower ‘racemes’ being sometimes branched again at the base); digitate, or subdigitate (the racemes often almost palmate, towards the culm tips); spatheate, or espatheate; a complex of ‘partial inflorescences’ and intervening foliar organs, or not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes ‘racemes’; the spikelet-bearing axes usually with more than 10 spikelet-bearing ‘articles’; solitary, or paired, or clustered; with very slender rachides; disarticulating; disarticulating at the joints. The pedicels and rachis internodes without a longitudinal, translucent furrow. ‘Articles’ linear; without a basal callus-knob; not appendaged; disarticulating transversely; densely long-hairy, or somewhat hairy, or glabrous. Spikelets paired (with a terminal triplet); 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 (save at the raceme base, where the spikelet pairs are homogamous). The ‘longer’ spikelets male-only, or sterile.
Female-sterile spikelets. The pedicellate spikelets male or sterile, awnless. The lemmas awnless.
Female-fertile spikelets. Spikelets compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present. Callus blunt.
Glumes two; relatively large; more or less equal; long relative to the adjacent lemmas; awnless; very dissimilar (the lower bicarinate, the upper narrower and naviculate). Lower glume two-keeled; convex on the back to flattened on the back; not pitted; relatively smooth; 5–9 nerved. Upper glume 1–4 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; not becoming indurated.
Female-fertile florets 1. Lemmas reduced to a linear, hyaline stipe, produced into the awn; less firm than the glumes; not becoming indurated; entire; awned. Awns 1; median; apical; geniculate; hairless (glabrous); much longer than the body of the lemma. Lemmas hairless; non-carinate; 1–3 nerved. Palea present, or absent; when present, very reduced; not indurated; nerveless. Lodicules present; 2; free; fleshy; glabrous. Stamens 1–3. 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; compressed dorsiventrally. Hilum short. Embryo large. Endosperm hard.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present. Intercostal papillae over-arching the stomata, or not over-arching the stomata; consisting of one oblique swelling per cell. Intercostal zones with typical long-cells (sometimes?), or exhibiting many atypical long-cells to without typical long-cells. Mid-intercostal long-cells rectangular; having markedly sinuous walls, or having markedly sinuous walls to having straight or only gently undulating walls. Microhairs present; panicoid-type; (42–)48–78(–84) microns long; (4.2–)5.1–6(–7.5) microns wide at the septum. Microhair total length/width at septum 9–14. Microhair apical cells (12–)21–28.5(–32) microns long. Microhair apical cell/total length ratio (0.29–)0.39–0.49(–0.51). Stomata common; 27–30 microns long. Subsidiaries low dome-shaped, or triangular (mostly). Intercostal short-cells common, or absent or very rare; when present, in cork/silica-cell pairs; silicified. Intercostal silica bodies vertically elongated-nodular, or cross-shaped, or oryzoid-type. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; cross shaped, or dumb-bell shaped.
Transverse section of leaf blade, physiology. C4; XyMS–. PCR cell chloroplasts with reduced grana; centrifugal/peripheral. Mesophyll with radiate chlorenchyma. Leaf blade ‘nodular’ in section (rarely), or adaxially flat; with the ribs more or less constant in size (rarely). Midrib conspicuous; with one bundle only, or having a conventional arc of bundles; with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups (sometimes, in places), or not present in discrete, regular adaxial groups (irregularly grouped, or the epidermis extensively bulliform); in simple fans (sometimes), or associated with colourless mesophyll cells to form deeply-penetrating fans (these mostly irregular). 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, or in three or more rings.
Phytochemistry. Leaves without flavonoid sulphates (1 species).
Cytology. Chromosome base number, x = 10. 2n = 20, 40, 50, and 60. 2, 4, 5, and 6 ploid.
Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Anthistiriinae. About 16 species.
Distribution, phytogeography, ecology. Old World Tropics.
Commonly adventive. Helophytic to xerophytic; species of open habitats; glycophytic. Habitats from marshes to subdesert and disturbed ground.
Economic aspects. Significant weed species: D. annulatum, D. aristatum, D. caricosum, D. papillosum. Important native pasture species: D. caricosum, D. sericeum.
Hybrids. Intergeneric hybrids with Bothriochloa.
Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: ‘Uromyces’ clignyi and Puccinia cesatii. Smuts from Ustilaginaceae. Ustilaginaceae — Sphacelotheca and Tolyposporella.
References, etc. Leaf anatomical: Metcalfe 1960; studied by us - D. annulatum (Forssk.) Stapf.
Illustrations. • Dichanthium aristatum, as Andropogon: Kunth (1835). • Dichanthium annulatum: Gibbs Russell et al., 1990. • D. annulatum: Sanchez-Ken, Flora del Valle Tehuacán-Cuicatlán (2011). • Dichanthium fecundum: Gardner, 1952. • Dichanthium sericeum subspecies: Gardner, 1952. • Inflorescence detail (Dichanthium sericeum). • Inflorescence detail (Dichanthium sericeum).
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’.
