- Name also: Bur Marigold, Three-lobe Beggarticks, Threelobe Beggarticks, Three-part Beggarticks, Leafy-bracted Beggarticks
- Family: Daisy Family – Compositae, subfamily Asteroideae
(formerly Aster Family – Asteraceae)
- Growing form: Annual herb.
- Height: 10–60 cm (4–25 in.). Stem usually almost glabrous, dark brown–reddish brown.
- Flower: Single flower-like approx. 1–2 cm (0.4–0.8 in.) capitula surrounded by involucral bracts. Capitula’s ray-florets lacking; disc florets brownish yellow, tubular, small. Stamens 5. Pistil of 2 fused carpels. Involucral bracts in 2 rows, outer bracts (5–9) large, leafy, varying in size, green, with hairy and sometimes with toothed margins, inner bracts small, brown, with green edges, membranous–with membranous margins. Capitula solitary or borne in a corymbose cluster, erect.
- Leaves: Opposite, short-stalked, lowest stalks winged. Blade dark green, with three or sometimes more lobes (occasionally entire), lobes lowest ovate, large-toothed, teeth straight.
- Fruit: 4-edged, descending bristles along edges, dull, greyish greenish brown, approx. 5–8 mm (0.2–0.32 in.) long achene, tip with 2 (occasionally 3) barbed bristles.
- Habitat: Shores, ditches, puddles, wasteland, yards, fallow fields, field tracks, paths, seaweed piles.
- Flowering time: August–September.
Trifid bur marigold probably only spread to the wild with people, but nowadays it is more common than native greater bur-marigold (B. radiata). The species bear a close resemblance to each other. Trifid bur marigold is dark green and its leafy involucral bracts, which surround the capitula, are not as numerous as greater bur-marigold’s. The achene is also longer, dull and greyish brown. Unfortunately at the beginning of summer these features have not yet developed and trying to tell the species apart based on only the leaves can be difficult. Trifid bur-marigold and greater bur-marigold can also cross-breed in common habitats, and the offspring are usually large (see last photo).
Trifid bur-marigold is fonder than greater bur-marigold of man-made habitats. It clearly exploits the nitrogenous soil and thrives in eutrophied wetlands or water that is affected by manure. It has a tendency, however, to move into the wild to sea-shores and waterside meadows which are prone to flooding. Trifid bur-marigold has at least temporarily taken over habitats north of the Arctic Circle: separate stands that grow beyond the pale have been noted in Rovaniemi, Savukoski and Enontekiö.
Bur-marigolds spread mainly across water via their floating achenes, but the fruits have also adapted to be spread by animals as their hooked spines attach very tightly to the fur of passing animals. From the plant’s point of view a trouser-leg will do just as well and the achenes stick themselves on securely to any that pass. At some stage the tips break off and the achene falls to the ground – hopefully in a suitable place. Trifid bur-marigold’s achenes might be a nuisance, but the plant has also been used to good effect as a medicinal herb and for dying sheets.