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The grass genera of the world

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

Loudetia Hochst.

Excluding Loudetiopsis sensu lato

Habit, vegetative morphology. Annual (rarely), or perennial; caespitose. Culms (25–)40–500 cm high; herbaceous (usually erect, slender or robust); branched above, or unbranched above. The branching simple. Culm nodes hairy, or glabrous. Culm internodes solid, or hollow. Young shoots intravaginal. Leaves mostly basal, or not basally aggregated; non-auriculate; without auricular setae (but often with auricular hair tufts). Leaf blades linear (often rigid); narrow; not cordate, not sagittate; flat, or rolled (convolute); pseudopetiolate, or not pseudopetiolate; without cross venation; persistent. Ligule a fringed membrane (narrow), or a fringe of hairs; 0.5–3 mm long. Contra-ligule present (of hairs), or absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.

Inflorescence. Inflorescence paniculate; open, or contracted (rarely more or less spiciform); more or less ovoid; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary, or paired (long-pedicelled triplets in L. togoensis); not secund; pedicellate; consistently in ‘long-and-short’ combinations, or not in distinct ‘long-and-short’ combinations.

Female-fertile spikelets. Spikelets 6–25 mm long; brown; compressed laterally to not noticeably compressed; disarticulating above the glumes; disarticulating between the florets (disarticulating between the two florets, less readily or not at all between G2 and L1); with conventional internode spacings. Rachilla prolonged beyond the uppermost female-fertile floret (very rarely), or terminated by a female-fertile floret; hairless; the rachilla extension when present, naked. Hairy callus present. Callus short, or long; pointed, or blunt (oblong to linear, bidentate or obliquely pungent).

Glumes two; relatively large; very unequal; (the upper) long relative to the adjacent lemmas (nearly as long as the spikelet); coarsely hairy (with brown or black hair cushions), or hairless; without conspicuous tufts or rows of hairs; pointed, or not pointed; awned (the G2 may be setaceous-acuminate), or awnless; non-carinate; similar. Lower glume shorter than the lowest lemma; 3 nerved. Upper glume 3(–5) nerved. 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 (L. togoensis). Palea of the proximal incomplete florets when present, fully developed (membranous, two keeled). The proximal incomplete florets male, or sterile. The proximal lemmas awnless (muticous); 3 nerved, or 5 nerved (L. togoensis); more or less equalling the female-fertile lemmas to decidedly exceeding the female-fertile lemmas; less firm than the female-fertile lemmas to similar in texture to the female-fertile lemmas; not becoming indurated (papery to leathery, similar to G2).

Female-fertile florets 1. Lemmas similar in texture to the glumes to decidedly firmer than the glumes; not becoming indurated (more or less leathery); usually incised (shortly so, rarely entire); usually 2 lobed; not deeply cleft; awned. Awns 1; median; from a sinus; geniculate; hairy; much longer than the body of the lemma; entered by one vein; deciduous (usually), or persistent (L. phragmitoides). Lemmas hairy to hairless (pilose to glabrescent). The hairs not in tufts; not in transverse rows. Lemmas non-carinate (rounded on the back); having the margins inrolled against the palea; without a germination flap; 5–9 nerved; with the nerves non-confluent. Palea present (linear); relatively long; apically notched; awnless, without apical setae; thinner than the lemma; not indurated (membranous); 2-nerved; 2-keeled (the keels thick). Palea keels wingless. Lodicules present; 2; free; fleshy; glabrous; not or scarcely vascularized. Stamens 2(–3). Anthers penicillate (L. togoensis), or not penicillate; without an apically prolonged connective. Ovary apically glabrous; without a conspicuous apical appendage. Styles free to their bases. Stigmas 2; brown.

Fruit, embryo and seedling. Fruit slightly longitudinally grooved. Hilum long-linear. Embryo large.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Intercostal zones with typical long-cells, or exhibiting many atypical long-cells, or without typical long-cells (long-cells normal to cubical). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; 60–90(–106) microns long; 5.4–6.6 microns wide at the septum. Microhair total length/width at septum 12–14.5. Microhair apical cells 24–50 microns long. Microhair apical cell/total length ratio 0.37–0.5. Stomata common; 24–30 microns long. Subsidiaries low to high dome-shaped (mostly), or triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common, or absent or very rare (ignoring cells associated with macrohair bases). Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; mostly dumb-bell shaped; not sharp-pointed.

Transverse section of leaf blade, physiology. C4. The anatomical organization conventional (usually), or unconventional. Organization of PCR tissue when unconventional, Arundinella type. XyMS–. PCR sheath outlines uneven. PCR sheath extensions present. Maximum number of extension cells 1–5. PCR cell chloroplasts centrifugal/peripheral. Mesophyll with radiate chlorenchyma; exhibiting ‘circular cells’, or without ‘circular cells’ (absent from L. flavida and L. simplex); traversed by columns of colourless mesophyll cells. 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; in simple fans, or associated with colourless mesophyll cells to form deeply-penetrating fans (commonly linking with traversing columns of colourless cells); associating with colourless mesophyll cells to form arches over small vascular bundles. Many of the smallest vascular bundles unaccompanied by sclerenchyma (in L. simplex), or all the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present. Sclerenchyma all associated with vascular bundles.

Phytochemistry. Leaves without flavonoid sulphates (2 species).

Special diagnostic feature. The lower glume shorter than the female-fertile lemma.

Cytology. Chromosome base number, x = 6 and 12. 2n = 20, 24, 40, and 60.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Arundinelleae. Soreng et al. (2015): Panicoideae; Tristachyideae. About 26 species.

Distribution, phytogeography, ecology. Tropical and southern Africa, Madagascar, with 1 in South America.

Helophytic, or mesophytic, or xerophytic; species of open habitats; glycophytic. In savanna woodland, often on poor shallow soils.

Economic aspects. Significant weed species: L. simplex. Grain crop species: wild L. esculenta harvested in Sudan.

Rusts and smuts. Rusts — Phakopsora and Puccinia. Smuts from Ustilaginaceae. Ustilaginaceae — Sorosporium.

References, etc. Leaf anatomical: Metcalfe 1960; this project; photos of L. flavida and L. simplex provided by R.P. Ellis.

Illustrations. • L. acuminata: Fl. W. Trop. Afr. (1936). • General aspect (L. flavida): Gibbs Russell et al., 1990


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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: 13th November 2017. delta-intkey.com/grass’.

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