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The grass genera of the world

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

Louisiella C.E. Hubb. & Léonard

Habit, vegetative morphology. Perennial; rhizomatous, or decumbent. Culms herbaceous; branched above. Culm nodes hairy. Culm internodes spongy. Leaves not basally aggregated; non-auriculate. Leaf blades narrow; without cross venation; persistent. Ligule a fringed membrane (very short).

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

Inflorescence. Inflorescence paniculate; open; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets paired or in short appressed racemelets; secund (?); pedicellate.

Female-fertile spikelets. Spikelets 8–9 mm long; lanceolate; compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; very unequal; (the longer) long relative to the adjacent lemmas; hairless; awnless; non-carinate; very dissimilar (the lower very small, nerveless and truncate, the upper equalling the spikelet, long acuminate, strongly nerved). Lower glume 0 nerved. Upper glume 5–7 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; epaleate; sterile. The proximal lemmas long acuminate; awnless; 7–9 nerved; decidedly exceeding the female-fertile lemmas; similar in texture to the female-fertile lemmas; not becoming indurated.

Female-fertile florets 1. Lemmas lanceolate; similar in texture to the glumes to decidedly firmer than the glumes; not becoming indurated (membranous to leathery); entire; pointed; awnless; hairy to hairless (glabrous, with a scabrid or hairy tip); non-carinate; having the margins lying flat on the palea; with a clear germination flap; 5–7 nerved. Palea present; relatively long; entire (pointed); awnless, without apical setae; textured like the lemma; not indurated; 2-nerved (near the margins); keel-less. Lodicules present; 2; free; fleshy; glabrous; not or scarcely vascularized. Stamens 3. Anthers not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles fused to free to their bases. Stigmas 2; red pigmented.

Fruit, embryo and seedling. Fruit small (2.5 mm long). Hilum long-linear. Embryo large to small (up to 1/3 as long as the grain).

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present. Intercostal papillae over-arching the stomata; several per cell (numerous per cell, in 1-several (average 2) rows, and large and ornamented at the blade margin). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; 27–36 microns long; 15–21 microns wide at the septum. Microhair total length/width at septum 5.3–7.7. Microhair apical cells (3.9–)4.5–5.7(–6) microns long. Microhair apical cell/total length ratio 0.5–0.7. Stomata common; 19–24 microns long. Subsidiaries high dome-shaped and triangular; including both triangular and parallel-sided forms on the same leaf. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs. Costal short-cells neither distinctly grouped into long rows nor predominantly paired (‘short-cells’ much longer than usual, and the files interrupted by prickles). Costal silica bodies ‘panicoid-type’; small, cross shaped and dumb-bell shaped; not sharp-pointed.

Transverse section of leaf blade, physiology. C4; XyMS+. PCR sheath outlines uneven. Mesophyll with radiate chlorenchyma. Leaf blade ‘nodular’ in section; with the ribs more or less constant in size. Midrib not readily distinguishable (one slightly larger bundle); with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Special diagnostic feature. No Eriochloa-type ‘callus’.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Panicinae. 1 species (L. fluitans).

Distribution, phytogeography, ecology. Tropical Africa.

Hydrophytic, or helophytic (floating, or decumbent on mud).

References, etc. Leaf anatomical: studied by us.

Special comments. Fruit data wanting.

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.’.