CVIII. LEMNACEJE 
545 
Common throughout India, ascending to 9000 ft. — All regions (Britain, 
Lesser Duckweed). 
2. Lemna gibba, Linn. ; FI. Br. Ind. vi. 556. Root-fibre 
single. Fronds J in. diam., orbicular, upper surface flat, lower 
swollen, almost hemispherical. Stamens 2. Ovules 2-7. 
Still waters throughout India, ascending to 7000 ft. — All regions (Britain, 
Gibbous Duckweed). 
3. Lemna polyrhiza, Linn. ; FI. Br. Ind. vi. 557. Root-fibres 
several, clustered. Fronds in. diam., broadly ovate or 
orbicular, both surfaces nearly flat. Stamens 2. Ovules 1 or 2. 
Common throughout India, ascending to 5000 ft. — Temperate and tropical 
regions (Britain, Greater Duckweed). 
2. WOLFFIA. In honour of J. F. Wolff, a writer on Lemna. 
— Inhabits nearly all regions. 
Wolffia arrhiza, Wimm. ; FI. Br. Ind. vi. 557. Root-fibres 
none. Fronds less than ~ in. diam., upper surface flat, lower 
swollen. Flowers bursting through the upper surface ; spathe 
none. Anther 1, sessile. Ovule 1. 
Common, probably throughout India. — Europe (Britain, Rootless Duckweed). 
The smallest flowering plant in Britain. 
CIX. ALISMACE^E 
Marsh or aquatic herbs ; stems erect. Leaves radical, undivided. 
Flowers small, 2-sexual, paniculate. Perianth inferior ; segments 
6, free, in two series, the outer green, the inner petal-like. Sta- 
mens 6, hypogynous. Ovaries numerous, free, 1-celled, 1-ovuled, 
arranged in a ring or head. Achenes surrounded by the persistent, 
outer perianth-segments. — Nearly all parts of the world. 
ALISMA. Origin of name doubtful. — Temperate and tropical 
regions. 
Alisma Plantago, Linn. ; FI. Br. Ind. vi. 559. A scapose, 
aquatic herb ; root fibrous ; stems 1^-3 ft., base swollen. Leaves 
radical, undivided, entire, ovate-lanceolate, about 3| X 1^ in., base 
tapering or slightly cordate ; stalks 1|-10 in. Flowers small, 2- 
sexual, on long, slender, unequal stalks in bracteate whorls forming 
a large, terminal, pyramidal panicle. Perianth inferior ; segments 
6, free, in two series ; the outer small, green, persistent ; the inner 
larger, petal-like, pale pink, with yellow claws. Stamens 6. Ovaries 
2n 
