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.
This common aquatic plant, like other members of pratal and paludal formations, is found in Preglacial, Interglacial, and Late Glacial beds. In Arctic Europe, North Africa, West Asia, N.W. India, N. America it is found in the North Temperate and Arctic Zones. In Great Britain it is found in the Peninsula province, in the Channel, Thames, and Anglia provinces, except in Hunts; in the Severn province; in S. Wales, except in Radnor and Pembroke; in N. Wales, except in Montgomery and Merioneth; in the Trent, in the Mersey province, Humber, Tyne, and Lakes provinces. In the West Lowlands it is found generally, except in Kirkcudbright; in Edinburgh, Linlithgow, and in the E. Highlands, except in Fife, Stirling, Perth, and Elgin.
Three-lobed Butterbur is found by the sides of most rivers and even by streams, but always in moist places; often overgrown by the wealth of Willow-herbs, Bur Reed, Flag, or Horsetail, which vie with each other for the guardianship of the waterway. The stem is erect, with opposite, rather spreading branches, giving it a somewhat characteristic appearance. The leaves, as implied in the second Latin name, are 3-lobed, opposite, stalked, united below, with coarsely toothed segments.
Photo. Flatters & Garnett - Three-lobed Butterbur (Bidens Tripartita)
The flowerheads are erect, with terminal, nearly erect, not nodding, yellowish florets, which are solitary. The fruit is provided with 2-5 bristles or awns, a feature intended to be noted in the first Latin name.
The plant is usually 2-3 ft. high. The flowers are in bloom between July and September. Three-lobed Butterbur is deciduous, herbaceous, and perennial.
The flowerheads are inconspicuous, not always possessing a ray (in which the florets are female, ligulate), with bell-shaped disk florets. The lobes of the style are linear, and tipped with papillae. The plant grows amongst herbage, where it is unlikely to be visited by insects to any extent, and must therefore rely on self-pollination for the most part.
It is provided with pappus or awns, covered with turned-down prickles, for wind dispersal of its achenes. It is also furnished with hooks, which aid in dispersing the seeds by means of animals, the burs catching in the wool of sheep, etc.