Grass Genera of the World

L. Watson and M. J. Dallwitz

Leptochloa sens. lat.

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

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

Excluding Kengia

Habit, vegetative morphology. Annual, or perennial; rhizomatous, or stoloniferous, or caespitose, or decumbent. Culms woody and persistent, or herbaceous; branched above, or unbranched above; 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; without cross venation; persistent; rolled in bud; ligule present; an unfringed membrane to a fringed membrane.

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

Inflorescence. Inflorescence of spicate main branches (spiciform racemes); open; non-digitate (the racemes often whorled), or subdigitate. 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; secund (clearly so, in Leptochloa sensu stricto), or not secund (or scarcely so, in Diplachne); shortly pedicellate; usually more or less imbricate (Leptochloa), or not imbricate (usually, in Diplachne); not in distinct ‘long-and-short’ combinations.

Female-fertile spikelets. Spikelets 1–15 mm long (6–15 in Diplachne, 1–5(–7) in Leptochloa sensu stricto); 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; usually shorter than the spikelets, or about equalling the spikelets, or exceeding 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.

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 (in Leptochloa sensu stricto), or non-carinate (Diplachne); 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 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 short mesocotyl, or with a long mesocotyl. First seedling leaf with a well-developed lamina. The lamina broad; curved; 3–7 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; of similar wall thickness costally and intercostally, or differing markedly in wall thickness costally and 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 (9–)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’; 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, or with non-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, or with the ribs very irregular in sizes. 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 (?); at least sometimes associated with colourless mesophyll cells to form deeply-penetrating 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.

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.

Taxonomy. Chloridoideae; main chloridoid assemblage.

Distribution, ecology, phytogeography. About 45 species; 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.

Holarctic, Paleotropical, Neotropical, and Australian. Boreal, Tethyan, and Madrean. African, Madagascan, Indomalesian, and Neocaledonian. Eastern Asian and Atlantic North American. Mediterranean. Saharo-Sindian, Sudano-Angolan, and West African Rainforest. Indian, Indo-Chinese, Malesian, and Papuan. Caribbean, Amazon, Central Brazilian, Pampas, and Andean. North and East Australian and Central Australian. Southern Atlantic North American and Central Grasslands. Sahelo-Sudanian, Somalo-Ethiopian, South Tropical African, and Kalaharian. Tropical North and East Australian.

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

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

References, etc. Morphological/taxonomic: Lazarides 1980a. Leaf anatomical: Metcalfe 1960; this project.

Special comments. Tendencies previously used to separate Diplachne as a genus or Section of Leptochloa are indicated.

Cite this publication as: Watson, L., and Dallwitz, M. J. (1992 onwards). ‘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: 18th August 1999. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993 onwards, 1998), and Watson and Dallwitz (1994), and Watson, Dallwitz, and Johnston (1986) should also be cited (see References).