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The grass genera of the world

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

Limnopoa C.E. Hubb.

From the Greek limne (pool, lake) and poa (grass), re habitat.

Habit, vegetative morphology. Annual, or perennial; forming floating mats. Culms 5–25 cm high; herbaceous; branched above. Culm nodes glabrous. Leaves not basally aggregated; non-auriculate. Sheath margins free. The sheaths rather inflated. Leaf blades narrow (short); setaceous (towards the tips); without cross venation; persistent. Ligule a fringe of hairs.

Reproductive organization. Plants bisexual, all with bisexual spikelets; without hermaphrodite florets (the lower of the two in each spikelet male, the upper female).

Inflorescence. Inflorescence a single raceme (unilateral); contracted (reduced, spicate, terminal, the sessile spikelets embedded, the pedicellate ones closely applied to the hollowed rachis). Rachides hollowed. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets paired; secund; pedicellate; consistently in ‘long-and-short’ combinations. The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets hermaphrodite.

Female-fertile spikelets. Spikelets 3–4 mm long; abaxial; compressed dorsiventrally; disarticulating above the glumes; disarticulating between the florets. Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; more or less equal; shorter than the adjacent lemmas (but exceeding the small L2); dorsiventral to the rachis; hairless; awnless; non-carinate; similar (ovate, membranous). Lower glume 5–9 nerved (with three main veins). Upper glume 5–9 nerved (3–4 main veins). Spikelets with incomplete florets (with 2 florets, the lower male, the upper female). The incomplete florets proximal to the female-fertile florets. The proximal incomplete florets 1; paleate. Palea of the proximal incomplete florets fully developed. The proximal incomplete florets male. The proximal lemmas narrowly ovate, glabrous; awnless; 5–7 nerved; decidedly exceeding the female-fertile lemmas; less firm than the female-fertile lemmas (membranous); not becoming indurated.

Female-fertile florets 1. Lemmas elliptic, puberulous, about 2/3 the length of L1; decidedly firmer than the glumes; not becoming indurated (cartilaginous); entire; blunt; awnless; hairy (woolly); non-carinate; having the margins inrolled against the palea; with a clear germination flap; 5–7 nerved. Palea present; relatively long; entire; awnless, without apical setae; cartilaginous, hairy; about 5; 2-keeled. Lodicules present; 2; free; fleshy; glabrous; not or scarcely vascularized. Stamens 0 (three with long non-penicillate anthers, in the lower floret only). Ovary apically glabrous. Styles fused to free to their bases. Stigmas 2; red pigmented.

Fruit, embryo and seedling. Fruit small; compressed dorsiventrally. Hilum long-linear. Embryo small; not waisted.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present. Intercostal papillae over-arching the stomata; consisting of one symmetrical projection per cell. Intercostal zones exhibiting many atypical long-cells. Mid-intercostal long-cells rectangular, or fusiform; having straight or only gently undulating walls. Microhairs present (but very scarce); panicoid-type; (51–)57–60(–66) microns long; 9–11.4 microns wide at the septum. Microhair total length/width at septum 5–6.9. Microhair apical cells (34–)36–41(–45) microns long. Microhair apical cell/total length ratio 0.6–0.68. Stomata common; 21–27 microns long. Subsidiaries mostly dome-shaped. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; cross shaped and dumb-bell shaped (with sharp points - prickly); sharp-pointed (prickly crosses & dumb-bells).

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll Isachne-type. Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size. Midrib not readily distinguishable (but mid-zone of leaf distinguished by presence of air-spaces); with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent. Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Isachneae. Soreng et al. (2015): Micrairoideae; Isachneae. 1 species (L. meeboldii).

Distribution, phytogeography, ecology. India.

Hydrophytic (in tanks, forming a thick mass of tangled stems on the surface).

References, etc. Morphological/taxonomic: Hubbard 1943. Leaf anatomical: studied by us.

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.’.