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The grass genera of the world

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

Diplachne P. Beauv.

From the Greek diploos (double) and achne (a glume), referring to the two-lobed lemma.

~ Leptochloa

Type species: Type: D. fascicularis (Lam.) P.Beauv.

Excluding Kengia

Habit, vegetative morphology. Perennial; stoloniferous, or caespitose (some tall). Culms 30–270 cm high; herbaceous; unbranched above. Culm nodes glabrous. Culm internodes hollow. Leaves mostly basal, or not basally aggregated; non-auriculate. Leaf blades linear; broad, or narrow; flat, or rolled (often involute); without abaxial multicellular glands; without cross venation; persistent; rolled in bud. Ligule an unfringed membrane, or a fringed membrane, or a fringe of hairs (D. chloridiformis, D. monticola). Contra-ligule present (of hairs), or absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets; exposed-cleistogamous, or chasmogamous; with hidden cleistogenes, or without hidden cleistogenes. The hidden cleistogenes when present, in the leaf sheaths.

Inflorescence. Inflorescence of spicate main branches (a contracted panicle of spikelike racemes), or a single raceme (rarely), or paniculate; open; with capillary branchlets, or without capillary branchlets; digitate, or non-digitate; espatheate; not comprising ‘partial inflorescences’ and foliar organs. The racemes spikelet bearing to the base. Spikelet-bearing axes persistent. Spikelets not secund (or scarcely so); biseriate; subsessile to pedicellate; usually more or less not imbricate.

Female-fertile spikelets. Spikelets 6–15 mm long (narrow); not noticeably compressed to compressed dorsiventrally (more or less terete); disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; hairless (glabrous or scaberulous, the internode apices widened and oblique).

Glumes two; relatively large; very unequal to more or less equal; shorter than the spikelets; shorter than the adjacent lemmas; dorsiventral to the rachis, or lateral to the rachis, or displaced; hairless; glabrous; awnless; carinate; similar (membranous). Lower glume shorter than the lowest lemma; 1 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only, or with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets awnless.

Female-fertile florets 5–20. Lemmas not becoming indurated; entire, or incised; blunt; when incised, 2 lobed (bidentate); not deeply cleft; awnless, or mucronate (from the sinus), or awned. Awns when present, 1; from a sinus, or dorsal; from near the top; non-geniculate; much shorter than the body of the lemma. Lemmas hairy (the margins ciliate below, and usually with a tuft of hairs below the middle of the mid-nerve), or hairless. The hairs in tufts (usually), or not in tufts. Lemmas non-carinate (rarely keeled); 3 nerved. Palea present; entire (e.g. D. eleusine), or apically notched; not indurated (membranous); 2-nerved; 2-keeled. Palea keels hairy (ciliate, below). Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2; white.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small; compressed laterally, or compressed dorsiventrally. Hilum short. Pericarp free, or loosely adherent, or fused. Embryo large; not waisted. Endosperm hard; without lipid; containing compound starch grains. Embryo with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins meeting.

Seedling with a short mesocotyl. First seedling leaf with a well-developed lamina. The lamina broad; curved; 7 veined.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; costal, or intercostal, or costal and intercostal. Intercostal papillae not over-arching the stomata; consisting of one symmetrical projection per cell (finger-like). Long-cells similar in shape costally and intercostally (narrowly so); of similar wall thickness costally and intercostally (thin walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; more or less spherical; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs 12–18–19.5 microns long. Microhair basal cells 9 microns long. Microhairs 9 microns wide at the septum. Microhair total length/width at septum 1.3–2.2. Microhair apical cells (6.6–)9–9.6(–10.5) microns long. Microhair apical cell/total length ratio 0.46–0.58. Stomata common; 21–24 microns long. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; not paired (mostly solitary); silicified and not silicified. Intercostal silica bodies absent, or imperfectly developed. Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; saddle shaped.

Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.

C4; XyMS+. PCR sheath outlines even. PCR sheaths of the primary vascular bundles interrupted; interrupted both abaxially and adaxially. PCR sheath extensions absent. PCR cell chloroplasts centripetal. Mesophyll with non-radiate chlorenchyma. Leaf blade ‘nodular’ in section; with the ribs very irregular in sizes. Midrib conspicuous; having a conventional arc of bundles; with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.

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

Phytochemistry. Leaves without flavonoid sulphates (1 species).

Cytology. Chromosome base number, x = 10. 2n = 40 and 60. 4 and 6 ploid.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Eleusininae. 18 species.

Distribution, phytogeography, ecology. Tropical and subtropical.

Commonly adventive. Helophytic, or mesophytic, or xerophytic; shade species and species of open habitats; halophytic and glycophytic. Woodland, savanna, dry and swampy soils.

Economic aspects. Significant weed species: D. fascicularis, D. fusca.

Rusts and smuts. Smuts from Ustilaginaceae. Ustilaginaceae — Ustilago.

References, etc. Leaf anatomical: studied by us - D.e parviflora (R. Br.) Benth.

Illustrations. • D. fusca: Gibbs Russell et al., 1990. • D. muelleri: Gardner, 1952. • D. parviflora, inflorescence and spikelet: E. Hickman. • D. fusca, spikelet: this project. • D. fusca, floret: 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: 11th December 2017.’.