The grass genera of the world
Type species: Type: D. arabica Jacq. = D. retroflexa (Vahl) Panz.
Excluding Drake-Brockmania, Heterocarpha
Habit, vegetative morphology. Annual; caespitose to decumbent. Culms 15–120 cm high; herbaceous; unbranched above. Culm nodes glabrous. Culm internodes hollow. Young shoots intravaginal. Leaves not basally aggregated; non-auriculate. Leaf blades broad (rarely), or narrow; usually flat; without abaxial multicellular glands; without cross venation; persistent; rolled in bud. Ligule a fringed membrane (very narrow). Contra-ligule absent.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence of spicate main branches, or paniculate (a raceme of numerous small spikes which become deflexed at maturity, the lower spikelets of each spike often replaced by small deciduous branchlets); non-digitate. Inflorescence with axes ending in spikelets. Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes with substantial rachides; disarticulating, or persistent; when disarticulating, falling entire (the smaller laterals deciduous). Spikelets solitary; secund; biseriate; sessile.
Female-fertile spikelets. Spikelets 3.5–10 mm long; cuneate; adaxial; compressed laterally; disarticulating above the glumes; when with two or more florets, disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; hairless; the rachilla extension with incomplete florets. Hairy callus absent.
Glumes present; two; more or less equal; exceeding the spikelets; long relative to the adjacent lemmas (much exceeding them); dorsiventral to the rachis; pointed; awned (acuminate-aristate); carinate (subulate); very dissimilar, or similar (leathery or membranous, the lower often very asymmetrical). Lower glume much exceeding the lowest lemma; 1–2 nerved. Upper glume 1–2 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets.
Female-fertile florets 1–3. Lemmas pointed to incised; less firm than the glumes to similar in texture to the glumes (thinly membranous); not becoming indurated; not deeply cleft (acute to emarginate); awnless to mucronate; hairy (usually, pilose on the nerves), or hairless (glabrous in D. retroflexa); carinate (slightly), or non-carinate; 3 nerved. Palea present; awnless, without apical setae; 2-nerved. Lodicules present; 2; free; fleshy; glabrous; toothed. 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; ellipsoid; shallowly concave on the hilar side; trigonous. Hilum short. Pericarp fused. Embryo large. Endosperm hard; without lipid; containing compound starch grains. Embryo with an epiblast; with a scutellar tail; with an elongated mesocotyl internode; with one scutellum bundle. Embryonic leaf margins meeting.
Seedling with a long mesocotyl; with a loose coleoptile. First seedling leaf with a well-developed lamina. The lamina broad; curved; 9 veined.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; intercostal. Intercostal papillae not over-arching the stomata; consisting of one oblique swelling per cell to consisting of one symmetrical projection per cell (most intercostal long-cells with a papilla at one end). Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally (thin walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; more or less spherical to elongated; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs 30–34.5 microns long. Microhair basal cells 24 microns long. Microhairs 12(–13.5) microns wide at the septum. Microhair total length/width at septum 2.5–2.9. Microhair apical cells 7.5–10.5 microns long. Microhair apical cell/total length ratio 0.2–0.27. Stomata common; 45–46.5 microns long. Subsidiaries non-papillate; triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare; not paired. Intercostal silica bodies absent. Prickles common. Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; panicoid-type; cross shaped, or dumb-bell shaped, or nodular; sharp-pointed (via points on dumb-bell ends), or not sharp-pointed.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4; XyMS+. PCR sheath outlines uneven. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only. PCR sheath extensions absent. PCR cell chloroplasts centrifugal/peripheral. Mesophyll with radiate chlorenchyma. Leaf blade adaxially flat. Midrib not readily distinguishable; with one bundle only. Bulliforms in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; nowhere forming figures. Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 10. 2n = 20. 2 ploid.
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Eleusininae. 3 species.
Distribution, phytogeography, ecology. Tropical Africa, Asia.
Commonly adventive. Helophytic to mesophytic (in seasonally wet places); shade species, or species of open habitats; glycophytic. Savanna.
Economic aspects. Significant weed species: D. retroflexa.
References, etc. Leaf anatomical: this project.
Illustrations. • D. retroflexa: Gibbs Russell et al., 1990. • D. retroflexa, inflorescence detail: this project. • D. retroflexa, embryo LS: this project. Dinebra retroflexa. Epiblast, elongated mesocotylar internode. • D. retroflexa, abaxial epidermis of leaf blade: this project
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: 13th November 2017. delta-intkey.com/grass’.