This section is from the book "British Wild Flowers - In Their Natural Haunts Vol2-4", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
Although Duckweed is almost ubiquitous in its distribution it is not found, as can hardly perhaps be expected from its small size and fragile nature, in early plant-beds. In Great Britain it is found in every county except Radnor, Peebles, Sutherland, and the Shetlands, that is, it ranges as far north as the Orkneys. In Derbyshire, moreover, it is found at the height of 1200 feet. It is a native of both Ireland and the Channel Islands.
Duckweed is so common that one expects to find it in every aquatic habitat, but it is more addicted to still than running water, as, for instance, that in ditches, drains, ponds, pools, lakes, meres, and that in slow-flowing rivers. It is a member of the floating-leaf association.
There is a single root hanging down from the floating, flat, inversely egg-shaped frond, with no stem or leaf. The frond is subconvex below, and flattened at the sides. The young fronds are seated at first on older ones but become detached. Below they are paler green than above. They are compact, and the cells of the epidermis are lined with wavy walls.
Photo. L. R. J. Horn - Duckweed (Lemna Minor, L.)
The flower, which is rare, is enclosed in a membranous spathe, and is formed in a marginal depression in the frond. There are 2 stamens altogether, each a male flower, with slender anther-stalks, and they develop in succession. The style is long, the anthers didymous. The flowers are reduced to a spathe-like bract, the stamens and pistil in separate flowers.
The plant floats on the surface, being an aquatic. Flowers may be sought in June and July. It is a herbaceous annual, and propagated by offsets, or divisions of the frond.
When it flowers several bloom at once. The flowers are unisexual and monoecious. They are borne in grooves at the margin of the frond-like stems, with 2 male flowers with 1 stamen each, only developed in succession, and 1 female flower of 1 carpel. The anther-stalks are slender, the style is long. The anthers are 2-celled and open transversely and in pairs, with prickly pollen. The plant is adapted to pollination by water-insects, but flowers are rare. The stigma is mature first, but the anthers soon open.
The seeds are dispersed by water, sinking to the bottom in autumn, and remaining during the winter when germinating, to rise in spring, and grow in summer. Lesser Duckweed is aquatic.
Two fungi infest it: Reessia amoeboidea, which is rare, and Olpidium lemnae. A beetle, Donacia lemnae, the small China Mask (Caloclysta lemnata), a Heteropterous insect, Hebrus pusillus, and a fly, Hydrellia albilabris, are found on it.
Lemna, Theophrastus, is the Greek name for Duckweed, and minor refers to its small-sized frond.
Lesser Duckweed is called Creed, Dig-meat, Duck-Meat, Duck-pond Weed, Duckweed, Duke's Meat, Endmete, Greeds, Greens, Groves, Grozens, Jenny Green-teeth, Water Lentils, Mardling Swimming Herb, Toadspit. Jenny Green-teeth was also the name of a well-known Lancashire boggart who was supposed to haunt pits and pools, and from whom it has probably been transferred to the plant. It is called "in Latin Lens palustris or lacustris, in Shoppes Lenticula aquae, in English Water Lentils, in High Douch Lue Sen, in base Almaigne Water Simeen".
It is valuable as food for waterfowl, and for aquaria, aerating the water.1
1 The arrangement of the chlorophyll granules is interesting. In darkness they are ranged along the side and inner walls of the cells, in direct sunlight they lie along the lateral walls, where they are less exposed to intense light, whilst when the light is diffused they lie along the sides and the inner walls.
Essential Specific Characters:313. Lemna minor, L. - Roots blunt, stemless, frond flat, obovate, oblong, compressed, convex below, flowers from a cleft, in a spathe, plant monoecious.