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 wet, gravelly places, marshy places. The habit is prostrate, then ascending. The stem is spreading, much branched, slender. The leaves are narrow, lance-shaped, linear, fringed with hairs, not glandular, the ocreae or stipules close, short, not inflated, fringed with hairs, glandless. The flowers are in greenish-pink, erect or ascending, slender, loose, straight, solitary racemes or spikes, on slender stalks. The outer perianth-segments are glandular at the base only. The styles are 2-3, united half-way. The fruit, a nut, is smooth, shining, small, planoconvex, or 3-angled, flattened, as long as the outer perianth. The plant is 6-18 in. high, flowering in August and September, and is a herbaceous annual.
The habitat of this plant is marshes (hence palustris). The habit is erect. The radical leaves are narrowly lance-shaped, rounded, or run down the stem below, the stem-leaves are linear, lance-shaped, narrow below. The flowers are numerous, in distant, distinct, leafy whorls, yellowish-green. The outer perianth-segments are egg-shaped, oblong, with 2-3 short, bristle-like teeth, not so long as the inner perianth-segments, with a lance-shaped, entire point, and a prominent, narrow, oblong tubercle. The fruit is larger (2-3 times) than in R. maritimus. The plant is 1-2 ft. high, flowering in July and August, and is a herbaceous perennial.
The habitat of this plant is fields and waste places. In habit it is prostrate, rooting below, branched, smooth or glandular, nodes thickened, stalked, spotted red, yellow, green. The leaves are shortly stalked, egg-shaped, or oblong, lance-shaped, not spotted. The flowers are in a cylindrical raceme, terminal or lateral, the flower-stalk rough. The sepals are glandular and rough. The lower ocrese or stipules are loose not fringed, the upper shortly fringed. The styles are free, the stamens 5-6. The anthers do not project. The nut is flattened at the sides. The plant is 1-3 ft. high. It is in flower from July to September, and is a herbaceous annual.
The habitat of this plant is reservoir banks, damp gravelly places, or waste places. The habit is similar to the last, the leaves spotted, broadly lance-shaped, glandular below, wavy. The flowers are in long, slender, crowded racemes, the sepals exceeding the fruit. The ocreae are shortly fringed and loose. The calyx is glandular, and also the flower-stalk. The nut is flattened along the border. The height is from 1 to 3 ft. The flowers are in bloom between July and October. Spotted Persicaria is a herbaceous annual.
This plant is found around towns and villages, or waste places, and woods where game is preserved, being used as food for pheasants, etc. The habit is erect. The plant is not prickly. The leaves are heart-shaped, arrow-shaped, acute. The flowers are in cymose panicles. There are 8 stamens. The nut is 3-angled, acute, the angles entire. The plant is 1-2 ft. high, flowering from July to September, and is a herbaceous annual.
The habitat of this plant is waste places on dry soil, and it may be wild in English pastures. The habit is erect or ascending. The stems are wavy, with slender branches which are spreading, the tips bent-down. The longer leaves are fiddle-shaped, oblong to heart-shaped, blunt, the upper lance-shaped, acute. They soon wither. The margin is scalloped. The leaf-stalk is slender. The flowers are in a panicle with spreading branches, leafy throughout, in distant leafy whorls. The perianth-segments are triangular to ovate, veined, deeply toothed to above the middle, pale, wedge-shaped below, pitted, netted, the teeth short, straight. The tubercle is oblong, prickly. The fruit is ovate, acute. The plant is 6-18 in. high, flowering from July to September, and is a herbaceous perennial.
The habitat of this plant is old walls near houses, waste places. The leaves are spear-shaped to ovate, greyish-green, fiddle-shaped. The perianth-segments are not tubercled, and are more or less round, heart-shaped, entire, membranous. The flowers are green, polygamous. The plant is 1-2 ft. high, flowering in June and July, and is a herbaceous perennial.