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The grass genera of the world

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

Digitaria Haller

From the Latin digitus (finger), alluding to radiating inflorescence branches.

Finger Grasses.

Type species: Type: D. sanguinalis (L.) Scop.

Including Acicarpa Raddi, Digitariella De Winter, Elytroblepharum Steud., Elytroblepharum (Steud.) Schlecht., Eriachne Phil., Gramerium Desv., Sanguinaria Bub., Sanguinella Gleichen, Syntherisma Walt., Trichachne Nees, Valota Adans.

Excluding Acostia, Digitariopsis

Habit, vegetative morphology. Annual, or perennial; rhizomatous, or stoloniferous, or caespitose, or decumbent (sometimes sward forming). Culms (6–)15–300 cm high (or more?); herbaceous; amply to sparsely branched above, or unbranched above. The branching simple. Culm nodes glabrous. Culm leaf sheaths rounded. Culm internodes solid, or hollow. Leaves not basally aggregated; non-auriculate. Leaf blades linear to lanceolate; broad, or narrow; flat, or folded, or rolled; without cross venation; persistent; rolled in bud. Ligule usually an unfringed membrane. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets overtly heteromorphic (sometimes, notably regarding indumentum), or homomorphic. Plants inbreeding; exposed-cleistogamous, or chasmogamous; with hidden cleistogenes (very rarely), or without hidden cleistogenes. The hidden cleistogenes when present, in the leaf sheaths.

Inflorescence. Inflorescence nearly always of spicate main branches (rarely with some secondary branchlets or a single raceme); open, or contracted; digitate, or subdigitate, or non-digitate. Primary inflorescence branches 2–50; borne distichously, or inserted all around the main axis. Rachides hollowed, or flattened, or winged. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary, or paired to in triplets (usually in groups of 2–3); secund; pedicellate (except for two Malaysian species). Pedicel apices truncate, or discoid, or cupuliform. Spikelets imbricate, or not imbricate; consistently in ‘long-and-short’ combinations (and the longer-pedicelled members sometimes larger and/or hairier), or not in distinct ‘long-and-short’ combinations. The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets hermaphrodite.

Female-fertile spikelets. Spikelets elliptic, or lanceolate, or ovate, or obovate; abaxial; compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes one per spikelet, or two; very unequal (the lower tiny or suppressed); shorter than the adjacent lemmas, or long relative to the adjacent lemmas (i.e., the upper, sometimes); free; dorsiventral to the rachis; pointed, or not pointed; awnless; non-carinate; very dissimilar. Lower glume 0–0.4 times the length of the upper glume; when present, much shorter than half length of lowest lemma; 0–1 nerved, or 3 nerved (at the base). Upper glume gibbous or not; 3–7 nerved (rarely nerveless). Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; paleate, or epaleate. Palea of the proximal incomplete florets when present, reduced. The proximal incomplete florets sterile, or male. The proximal lemmas usually as long as the spikelet, usually hairy, the hairs between the first and second lateral nerves and along the margins (contrast with Stereochlaena); awnless; 3–7(–11) nerved; exceeded by the female-fertile lemmas to decidedly exceeding the female-fertile lemmas; less firm than the female-fertile lemmas; not becoming indurated.

Female-fertile florets 1. Lemmas similar in texture to the glumes to decidedly firmer than the glumes (cartilaginous); smooth to striate; yellow in fruit, or brown in fruit, or black in fruit; entire; pointed (mostly subacute to acuminate); awnless (but often apiculate); hairless (no more than minutely striate-papillate); non-carinate, or carinate (Section Monodactylae, where some species have a pronounced median keel); having the margins lying flat on the palea; with a clear germination flap; obscurely 1–3 nerved. Palea present; relatively long (about equalling the lemma); tightly clasped by the lemma; entire; awnless, without apical setae; textured like the lemma; 2-nerved. Lodicules present; 2; joined, or free; fleshy; glabrous. Stamens 3. Anthers not penicillate. Ovary apically glabrous. Styles fused, or free to their bases. Stigmas 2; red pigmented.

Fruit, embryo and seedling. Fruit small; compressed dorsiventrally. Hilum short. Embryo large; waisted. Endosperm hard; without lipid; containing compound starch grains. Embryo without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.

Seedling with a long mesocotyl; with a loose coleoptile. First seedling leaf with a well-developed lamina. The lamina broad; erect, or curved, or supine; 13–20 veined.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; (34–)42–75(–78) microns long; 3.6–7.5 microns wide at the septum. Microhair total length/width at septum 8–18.3. Microhair apical cells (17–)22–48(–50) microns long. Microhair apical cell/total length ratio 0.44–0.67. Stomata common; 24–36 microns long. Subsidiaries high to low dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare (scarce); not paired (solitary when seen); when seen, not silicified. Prickles sometimes common. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; cross shaped, or butterfly shaped, or dumb-bell shaped.

Transverse section of leaf blade, physiology. C4; biochemical type NADP–ME (D. sanguinalis); XyMS–. PCR sheath outlines uneven. PCR sheath extensions absent. PCR cells with a suberised lamella. PCR cell chloroplasts with reduced grana; centrifugal/peripheral. Mesophyll with radiate chlorenchyma. Leaf blade with distinct, prominent adaxial ribs, or ‘nodular’ in section, or adaxially flat; with the ribs more or less constant in size. 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. Bulliforms present in discrete, regular adaxial groups, or not present in discrete, regular adaxial groups (commonly in irregular groups); when regularly grouped, in simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present (rarely), or absent; nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.

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

Phytochemistry. Tissues of the culm bases with little or no starch (D. sanguinalis). Leaves without flavonoid sulphates (4 species).

Cytology. Chromosome base number, x = 9, 15, and 17. 2n = 18, 30, 36, 45, 54, 60, 70, 72, and 76, or 108. Chromosomes ‘small’. Nucleoli persistent.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Anthephorinae. 220 species.

Distribution, phytogeography, ecology. Mainly in warm regions.

Commonly adventive. Mesophytic, or xerophytic; mostly species of open habitats. Diverse habitats, including weedy ground and sandy beaches.

Economic aspects. Significant weed species: ‘crabgrasses’ -D. adscendens, D. decumbens, D. ciliaris, D. fuscescens, D. horizontalis, D. ischaemum, D. longiflora, D. radicosa, D. sanguinalis, D. scalarum, D. setigera, D. ternata, D. violascens. Cultivated fodder: D. decumbens, D. eriantha (Pangola). Important native pasture species: D. aridicola, D. didactyla, D. gazensis, D. longiflora, D. milanjiana, D. nodosa, D. pearsonii, D. velutina and others. Grain crop species: minor west African cereals on infertile soils: D. exilis (Achna, Fonio), D. iburua. Lawns and/or playing fields: D. didactyla, D. longiflora, D. swazilandensis, D. timorensis.

Rusts and smuts. Rusts — Physopella and Puccinia. Taxonomically wide-ranging species: Puccinia levis, Puccinia substriata, and Puccinia esclavensis. Smuts from Tilletiaceae and from Ustilaginaceae. Tilletiaceae — Tilletia. Ustilaginaceae — Sorosporium, Sphacelotheca, and Ustilago.

References, etc. Leaf anatomical: Metcalfe 1960; studied by us - D. aequiglumis (Hackel ex Arechav.) Parodi, D. ammophila (F. Muell.) Hughes, D. bicornis (Lam.) Roem. & Schult., D. breviglumis (Domin) Henr., D. brownii (Roemer & Schultes) Hughes, D. coenicola (F. Muell.) Hughes, D. divaricatissima (R. Br.) Hughes, D. milanjiana (Rendle) Stapf, D. parviflora (R. Br.) Hughes, D. sanguinalis (L.) Scop.

Illustrations. • D. gibbosa, as Panicum: Kunth (1835). • D. exilis: Hook. Ic. Pl. 31 (1916). • D. iburua: Hook. Ic. Pl. 31 (1916). • D. sanguinalis: Gardner, 1952. • D. sanguinalis: Gibbs Russell et al., 1990. • D. tricholaenoides: Wood, Natal Plants 2 (1904). • D. ischaemum (as humifusum), general aspect: Eng. Bot. (1872). • Ligule of D. sanguinalis. • Back of rachis of D. sanguinalis. • ‘Front’ of rachis of D. sanguinalis. • Female-fertile lemmas: Webster (1983). • D. bicornis, abaxial epidermis of leaf blade: this project. • D. longiflora, abaxial epidermis of leaf blade: this project. • D. sanguinalis, abaxial epidermis of leaf blade: this project. • D. brownii, abaxial epidermis of leaf blade: this project. • D. brownii, TS leaf blade - mature minor bundles: this project. • D. parviflora, T.S. leaf blade midrib: this project. • D. parviflora, T.S. lateral part 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: 11th December 2017.’.