I. Three-lobed Butterbur (Bidens tripartita, L.). 2. Coltsfoot (Tussilago Farfara, L.). 3. Butterbur (Petasites ova/us, Hill; officinalis, Maench). 4. .Marsh Ragwort (Senecio aquatius, Hill). 5. Marsh Thistle (Cnicuts palustris, Willd.). 6. Great Yellow Loosestrife (Lysimachia vulgaris, L.).

The plant is aquatic or semi-aquatic, and a peat-loving plant requiring a peaty soil, growing in the reed swamp.

Two flies, Tephritis elongatula, Chromatomyia albiceps, are found on it.

Bidens, Linnaeus, is from the Latin bis, twice, dens, a tooth, in allusion to the two or more teeth or awns crowning the fruit, and the second Latin name refers to the 3-lobed leaf characters.

Water Agrimony and Bur Marigold Double-tooth are the common names in most general use.

It has been used to dye linen and wool a yellow colour, yarn and flax being first steeped in alum water, dried, and steeped in a preparation of this plant, and then boiled in it.

Essential Specific Characters:156. Bidens tripartita, L. - Stem branched, branches opposite, leaves petiolate, trifid, flowerheads small, yellow, suberect, solitary, terminal.