This section is from the book "British Wild Flowers - In Their Natural Haunts Vol5-6", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
The habitat of this plant is marshes and bogs. The habit is prostrate. The stem is creeping or floating, white. The leaves are shield-shaped (hence Hydrocoiyle), rounded, scalloped, glossy, g-veined. The leaf-stalk is hairy, exceeding the flower-stalks. The flowers are small, purplish-green, stalkless (like the fruit, which is seldom produced), forming a head. The umbels or heads are simple, proliferous in the centre, with a second head, 5-flowered, notched below, axillary. The bracts are very small, triangular, hollow. The fruit is small, the carpels having resinous points, purplish dots with 2 ridges on each face. The styles are slender on a flattened disk. The plant is creeping, flowering from May to August, and is a herbaceous perennial.
The habitat of this species is ditch-banks and brooks, marshy, watery places. The plant is prostrate in habit, then erect. The stem is rooting at the base, and slender. The leaves are pinnate, or trifoliate. The leaflets are stalkless, egg-shaped, lance-shaped, oblong, unequally bluntly toothed, or lobed. The flowers are small, white, in more or less stalkless or stalked umbels, with leaves opposite, longer than the flower-stalks, with a partial involucre of several leaves. The rays are unequal. The bracteoles are numerous, oblong, with a membranous margin. There are no bracts, or 1-2. The general involucre of 1-3 leaflets soon falls. The fruit is small. The styles are short, spreading. The plant is 1-3 ft. in height, and flowers in July and August, being a herbaceous perennial.
The habitat of this plant is marshes, fresh and salt. The habit is erect. The root fibres are not tuberous, but club-shaped, fleshy (tapering at both ends), cylindrical. The stem is slightly branched. The radical leaves are bi-pinnate, soon disappearing, the segments are bluntly lobed, oblong, wedge-shaped, the leaflets 2-3 lobed, the lower stem-leaves are 2-3 times pinnate, the leaflets linear, acute, the upper leaves are pinnate. The flowers are white. The partial umbels are loose, spherical, distinct. The general involucre consists of many leaves, and is sometimes wanting. The partial involucre consists of many leaves not so long as the barren florets. The outer florets are long-stalked, barren as a rule. The inner are more or less stalkless, fertile. The petals, radiant, are inversely heart-shaped, round, with a short, narrow stalk, divided to the middle. The fruit is oblong, not corky below, rounded above, inversely egg-shaped, rounded and narrowed above. The styles are short and slender, as are the ultimate flower-stalks. The plant is 1-4 ft. high, flowering from July to September, and is a herbaceous perennial.
The habitat of this species is marshes and ditches. The habit is erect. The rootstock consists of large spindle-shaped tubers. The juice is yellow or colourless. The leaves are large, triangular. The stem is much branched, 3-4 times pinnate, the radical leaves 2-3 pinnate, the stem-leaves deeply divided to the base. The leaflets are broad, stalked, wedge-shaped, 2-3 lobed, oblong, round, cut, the lobes of the upper leaves not so broad. The leaf-stalks are sheathing, large. The flowers are white, in numerous large umbels with many rays. The bracts and bracteoles are numerous or wanting. The involucral leaves vary in number and shape. The fruit is entire, narrow, oblong, more or less cylindrical, furrowed, longer than the fruit-stalk, which is not thickened. The plant is 2-5 ft. high, flowering in July and August, and is a herbaceous perennial.