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The grass genera of the world

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

Leptochloa P. Beauv. sensu stricto

From the Greek leptos (slender) and chloë (a grass), referring to inflorescences.

Including Anoplia Steud., Baldomiria Herter, Diachroa Nutt, Diacisperma Kuntze, Disakisperma Steud., Ipnum Phil., Leptostachys Meyer, Oxydenia Nutt, Rabdochloa P. Beauv.

Excluding Diplachne, Kengia, Trichloris

Habit, vegetative morphology. Annual, or perennial; rhizomatous, or stoloniferous, or caespitose, or decumbent. Culms woody and persistent, or herbaceous; usually sparsely branched above, or unbranched above. The branching simple. Culms tuberous, or not tuberous. Culm nodes glabrous. Culm internodes solid, or hollow. Leaves mostly basal, or not basally aggregated; non-auriculate. Leaf blades linear, or linear-lanceolate; narrow; flat, or rolled; without abaxial multicellular glands; not pseudopetiolate; 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 all alike in sexuality. Plants exposed-cleistogamous, or chasmogamous; without hidden cleistogenes.

Inflorescence. Inflorescence of spicate main branches (spiciform racemes); open; non-digitate (the racemes often whorled), or subdigitate. Inflorescence with axes ending in spikelets. Rachides hollowed, or flattened, or neither flattened nor hollowed, not winged. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. The racemes spikelet bearing to the base. Spikelet-bearing axes with very slender rachides; persistent. Spikelets solitary; clearly secund; shortly pedicellate; usually imbricate; not in distinct ‘long-and-short’ combinations.

Female-fertile spikelets. Spikelets 1–5 mm long (rarely up to 7 mm); adaxial; compressed laterally to not noticeably compressed; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; hairless. Hairy callus present, or absent. Callus short (minute); blunt.

Glumes two; very unequal to more or less equal; shorter than the spikelets; usually shorter than the adjacent lemmas; free (narrow, membranous); dorsiventral to the rachis (the lower often asymmetric); hairless; pointed; awnless; carinate. 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. Spikelets without proximal incomplete florets.

Female-fertile florets (1–)3–6. Lemmas less firm than the glumes to similar in texture to the glumes (membranous to hyaline); not becoming indurated; entire (rarely), or incised; when entire, blunt; when incised, 2 lobed (bidentate); when incised, not deeply cleft; awnless, or mucronate, or awned. Awns when present, 1; from a sinus; non-geniculate; much shorter than the body of the lemma. Lemmas hairy (with appressed hairs on the lateral nerves), or hairless; usually more or less carinate; 3 nerved. Palea present; entire to apically notched; awnless, without apical setae; not indurated (membranous); 2-nerved; 2-keeled (often glabrous between the keels, but hairy outside them). Lodicules present; 2; free; fleshy. Stamens 2–3. Anthers not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit adhering to lemma and/or palea, or free from both lemma and palea; small (0.5–2 mm long); compressed laterally, or compressed dorsiventrally; smooth (or striolate). 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 long mesocotyl. First seedling leaf with a well-developed lamina. The lamina broad; curved; 3–5 veined.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae nearly always present; intercostal. Intercostal papillae over-arching the stomata, or not over-arching the stomata; consisting of one oblique swelling per cell, or consisting of one symmetrical projection per cell. Long-cells similar in shape costally and intercostally; differing markedly in wall thickness costally and intercostally (thicker intercostally). Intercostal zones with typical long-cells, or exhibiting many atypical long-cells (many long-cells very short). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; more or less spherical to elongated; nearly always clearly two-celled, or ostensibly one-celled (rarely); chloridoid-type (of various forms, but very rarely of the ostensibly one-celled type). Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs with ‘partitioning membranes’ (in L. digitata). The ‘partitioning membranes’ in the basal cell. Microhairs (13–)19.5–36(–42) microns long. Microhair basal cells 27–30 microns long. Microhairs (5.4–)9–10(–18) microns wide at the septum. Microhair total length/width at septum 1.3–3.3. Microhair apical cells (6–)7–15(–16.5) microns long. Microhair apical cell/total length ratio 0.21–0.7(–1). Stomata common; 15–25.5 microns long. Subsidiaries low dome-shaped to triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs, or not paired (solitary); silicified, or not silicified. Intercostal silica bodies absent, or imperfectly developed. 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; saddle shaped, or tall-and-narrow to crescentic, or ‘panicoid-type’; when panicoid type, cross shaped, or dumb-bell shaped; not sharp-pointed.

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

C4; biochemical type PCK (L. ciliolata), or NAD–ME (L. digitata); XyMS+. PCR sheath outlines uneven, or even. PCR sheaths of the primary vascular bundles interrupted; interrupted both abaxially and adaxially. PCR sheath extensions present, or absent. Maximum number of extension cells when present, 1. PCR cells with a suberised lamella, or without a suberised lamella. PCR cell chloroplasts ovoid, or elongated; with well developed grana; centrifugal/peripheral (L. ciliolata), or centripetal. Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells, or not traversed by colourless columns. Leaf blade ‘nodular’ in section; 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 (?); in simple fans, or associated with colourless mesophyll cells to form deeply-penetrating fans (at least sometimes). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.

Phytochemistry. Leaves without flavonoid sulphates (1 species). Leaf blade chlorophyll a:b ratio 3.41–4.26.

Cytology. Chromosome base number, x = 10. 2n = 20, 40, and 60. 2, 4, and 6 ploid. Nucleoli persistent.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae. 27 species.

Distribution, phytogeography, ecology. Tropical and subtropical.

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

Economic aspects. Significant weed species: L. chinensis, L. coerulescens, L. fascicularis, L. filiformis, L. panicea, L scabra, L. uninervia, L. virgata. Important native pasture species: e.g. L. chinensis, L. dubia, L. obtusiflora, L. panicea.

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

References, etc. Morphological/taxonomic: Lazarides 1980a. Leaf anatomical: Metcalfe 1960; studied by us - L. decipiens (R. Br.) Stapf ex Maiden, L. digitata (R. Br.) Domin, L. filiformis (Lam.) Beauv., L. neesii (Thw.) Benth., L. panicea (Retz.) Ohwi, L. virgata (L.) P. Beauv.

Special comments. Note that there are serious taxonomic problems involving Leptochloa, Trichoneura, Diplachne, etc. Illustrations. • L. virgata: P. Beauv. (1812). • L. digitata: Gardner, 1952. • General aspect (L. panicea): Gibbs Russell et al., 1990. • Spikelet close-up (L. digitata). • L. digitata, abaxial epidermis of leaf blade: this project. • L. digitata, TS of leaf blade: this project. • Microhairs of L. digitata and Eleusine indica: 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.’.