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The grass genera of the world

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

Dactyloctenium Willd.

From the Greek daktylos (finger) and ktenion (a little comb), alluding to the digitate inflorescences.

Type species: Type: D. aegyptium (L.) Willd. as D. aegyptiacum.

Habit, vegetative morphology. Annual, or perennial; rhizomatous, or stoloniferous, or caespitose, or decumbent (mostly low, sometimes sward-forming). Culms 5–100(–160) cm high; herbaceous. The branching suffrutescent (D. robechii), or simple. Culm nodes glabrous. Culm internodes solid, or hollow. Leaves not basally aggregated; non-auriculate. Leaf blades linear to linear-lanceolate (sometimes pungent); narrow; flat, or rolled; not needle-like; without abaxial multicellular glands; without cross venation; persistent; once-folded in bud. Ligule a fringed membrane (narrow), or a fringe of hairs.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality (or terminal spikelets sterile). Plants exposed-cleistogamous, or chasmogamous.

Inflorescence. Inflorescence of spicate main branches (the mature spikelets sometimes almost at right-angles to the rachides); digitate. Primary inflorescence branches 2–11. Inflorescence axes not ending in spikelets (produced into a flattened point). Rachides flattened. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes with substantial rachides; disarticulating (sometimes very tardily); falling entire. Spikelets secund; biseriate; imbricate (sometimes becoming pectinate).

Female-fertile spikelets. Spikelets 2.3–8 mm long; adaxial; compressed laterally; disarticulating above the glumes; usually not disarticulating between the florets (the rachilla tough). Rachilla prolonged beyond the uppermost female-fertile floret; hairless; the rachilla extension with incomplete florets. Hairy callus absent.

Glumes two (persistent, membranous, laterally compressed); more or less equal; shorter than the spikelets; shorter than the adjacent lemmas; lateral to the rachis (the lower side-on); hairless; the upper awned (or mucronate from just below the tip), or awnless (the lower); carinate; very dissimilar (membranous, the lower muticate, the upper obliquely awned or mucronate from just below the tip). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets.

Female-fertile florets 3–6. Lemmas acute to shortly awned, often recurved at the tip; not becoming indurated (thinly membranous); entire, or incised; awnless, or mucronate, or awned. Awns when present, 1; median; apical; non-geniculate; straight, or recurving; much shorter than the body of the lemma. Lemmas hairless; glabrous; strongly carinate; having the margins lying flat on the palea; 1–3 nerved. Palea present; relatively long; apically notched; awnless, without apical setae; 2-nerved; 2-keeled. Palea keels winged (often), or wingless. Lodicules present; 2; fleshy. Stamens 3. Anthers 0.25–2.3 mm long; not penicillate. Ovary apically glabrous. Styles fused. Stigmas 2.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small (0.7–1.1 mm long); ellipsoid to subglobose; obtusely triquetrous; sculptured. Hilum short. Pericarp thin (hyaline); free. Embryo large; not waisted. Endosperm containing compound starch grains. Embryo with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins meeting.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; costal and intercostal. Intercostal papillae over-arching the stomata; consisting of one oblique swelling per cell to consisting of one symmetrical projection per cell (large and thick walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls and having straight or only gently undulating walls. Microhairs present; more or less spherical; ostensibly one-celled, or clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs with ‘partitioning membranes’ (in D. aegyptium). The ‘partitioning membranes’ in the basal cell. Microhairs 13–17 microns long. Microhair basal cells 15 microns long. Microhair total length/width at septum 1–1.5. Microhair apical cell/total length ratio 0.4. Stomata common. Subsidiaries low dome-shaped, or dome-shaped and triangular. Guard-cells overlapped by the interstomatals (regardless of the overlapping papillae). Intercostal short-cells common (rarely), or absent or very rare; not paired. Intercostal silica bodies absent. Costal short-cells conspicuously in long rows, or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies present in alternate cell files of the costal zones; consistently saddle shaped, or horizontally-elongated smooth and saddle shaped (sometimes, then the saddles predominating).

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 complete. PCR sheath extensions present. Maximum number of extension cells 1. PCR cell chloroplasts with well developed grana; centrifugal/peripheral. Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells, or not traversed by colourless columns. Leaf blade adaxially flat. Midrib conspicuous; having a conventional arc of bundles; with colourless mesophyll adaxially (the colourless tissue extending laterally across the adaxial part of the blade). Bulliforms present in discrete, regular adaxial groups; in simple fans, or associated with colourless mesophyll cells to form deeply-penetrating fans (the material of D. aegyptium seen having deep-penetrating simple fans only). All the vascular bundles accompanied 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 and 12. 2n = 20, 36, and 48. 2, 3, and 4 ploid.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae. 13 species.

Distribution, phytogeography, ecology. In warm regions.

Commonly adventive. Mesophytic to xerophytic; species of open habitats; halophytic and glycophytic. Sometimes in saline habitats or dunes, mostly in dry sandy soils.

Economic aspects. Significant weed species: D. aegyptium. Cultivated fodder: D. giganteum. Important native pasture species: D. aegyptium (in arid and semiarid places). Lawns and/or playing fields: D. aegyptium (Crowfoot, Durban grass).

Rusts and smuts. Rusts — Puccinia. Smuts from Tilletiaceae and from Ustilaginaceae. Tilletiaceae — Tilletia. Ustilaginaceae — Ustilago.

References, etc. Leaf anatomical: Metcalfe 1960; studied by us - D. aegyptium (L.) Beauv.

Illustrations. • D. radulans: Gardner, 1952. • D. giganteum: Gibbs Russell et al., 1990. • Inflorescence (D.radulans). Dactyloctenium radulans. Digitate racemes with naked tips. • Dorsiventral rachis (D. radulans). Dactyloctenium radulans. Rachis tip naked, flattened. • Fruit (D. australe). • Spikelet (D. australe). • Upper glume (D. australe). • Microhairs of D. aegyptium and Sporobolus elongatus: longitudinal EM sections (Amarasinghe)

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.’.