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 525 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; a fringe of hairs.
Reproductive organization. Plants bisexual, 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 34 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 59 nerved (with three main veins). Upper glume 59 nerved (34 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; 57 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; 57 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 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)5760(66) microns long; 911.4 microns wide at the septum. Microhair total length/width at septum 56.9. Microhair apical cells (34)3641(45) microns long. Microhair apical cell/total length ratio 0.60.68. Stomata common; 2127 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.
Taxonomy. Panicoideae; Panicodae; Isachneae.
Distribution, ecology, phytogeography. 1 species; India. Hydrophytic (in tanks, forming a thick mass of tangled stems on the surface).
Paleotropical. Indomalesian. Indian.
References, etc. Morphological/taxonomic: Hubbard 1943. Leaf anatomical: this project.
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.’ http://biodiversity.uno.edu/delta/. 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).