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.
Aquatic but delicate, no evidence of its occurrence in early beds is forthcoming. It is found in the N. Temperate Zone in Europe and N. Asia. In Great Britain it does not grow in Cornwall or N. Devon; in the Peninsula and Channel provinces; not in Wilts or Isle of Wight, N. Hants; but in the whole of the Thames province, Anglia, Severn province, except in Mid Lancs; in the Humber province, except in S.E. Yorks, i.e. from Durham to Devon and Kent. It is local in Ireland.
This is one of those local plants which have been further rendered scarce owing to lack of suitable habitat by modern drainage. It is found in little pools and ditches of a still nature, leading into larger rivers and estuaries, many of which originate in flood time, but afterwards disappear, hence doubtless its mode of reproduction. It is found also in isolated ponds.
Frogbit is a floating plant with only erect flowering stems, and leaves in clusters at points where roots strike downward and root deeply in the mud below; or it may be floating loose, especially in deeper water. The plant multiplies largely by hibernacula, or stolons, or short shoots, with fibrous roots developing shoots and new leaves which fall off and sink to the bottom. The leaves are stalked, rounded, kidney-shaped, fleshy, and smooth.
The plant is dioecious, and the flowers are erect, white, large, with a yellow patch at the base, and yellow anthers. The petals are delicate, inversely egg-shaped. The flowers spring in pairs from a transparent membranous sheath at the base of the flower-stalk. Frog-bit, however, does not always flower, and seldom produces any seed.
The flower-stems are 3-4 in. Frogbit blooms in July and August. It is a herbaceous perennial, propagated by division.
The flowers are dioecious and produced on the surface. The 12 stamens are partly without anthers (3-6). The anthers are fixed by the base. The plant is usually pollinated by the wind, but is largely propagated by bulbils, being stoloniferous. In winter it is kept alive by buds from the stolons or hibernacula. Honey is also secreted in 3 glands in the crown of the ovary or base of the petals, and is half concealed, but insects do not often visit the flower.
Photo. J. J. Ward - Frogbit (Hydrocharis Morsus-ranae, L.)
Ripe fruit is almost unknown. The manner of opening is irregular, and the small seeds are blown out from their lightness. But the plant does not often produce fruit and seeds, as it seldom flowers.
The plant is aquatic, being a member of the floating-leaf association.
Two beetles, Galeruca sagittarii and Donacia menyanthidis, are found on it.
Hydrocharis, Linnaeus, is from the Greek hudor, water, charis, elegance, grace. Morsus-ranae, Dodonaeus, is from morsus, bitten, rana, frog, because the margin was supposed to be bitten by frogs.
The only name by which it is known is Frogbit.
Essential Specific Characters:288. Hydrocharis morsus-ranae, L. - Plant floating with runners, leaves tufted, reniform, entire, smooth, purplish below, flowers white, from a pellucid sheath, sepals green.