Bidens tripartita aka Three Lobe Beggar Ticks

Bidens tripartita is an annual in the daisy family, Asteraceae. Its common names include bur marigold and water agrimony. It is native to Britain and much of Europe. Its range extends through North Africa and Asia to New Guinea. It grows in open, wet places, such as ditches and stream banks. Other habitats include lake shores, wet pastures and rice fields. These sites reflect its need for damp ground and sun.

The plant grows upright and has many branches. Garden references give a height of about 2 feet [0.6 metres]. They give a spread of about 1 foot [0.3 metres]. A broader account describes plants reaching 3.3 feet [1 metre]. Some reach 4.9 feet [1.5 metres], beyond the stated garden size. It flowers from July to September. Each flower has both male and female organs. Bees and hoverflies pollinate the flowers during the flowering season.

The seeds have backward-pointing prickles on their outer coats. These hooks catch on clothes and animal fur. This helps carry the seeds to new places. Both plant accounts warn of a risk near fish ponds. Seeds can catch in goldfish gills and have caused deaths. This is a physical hazard linked to the seed hooks. Burning the flower heads releases a scent like cedar or resin.

Grow it in full sun, in damp or wet soil. The plant does not grow in shade, according to PFAF. It accepts sand, loam and clay with moderate fertility. It also tolerates mildly acid, neutral and mildly alkaline soil. Bog gardens and damp beds suit its growing needs. PFAF lists USDA hardiness zones 5–9 for this annual. Sow seeds where they will grow in early spring. Cover them with only a thin layer of soil. Keep the seedbed damp while waiting for shoots. Germination takes two to three weeks at 15°C.

People cook the young leaves for food. Wild plants also provide medicine and dye materials. Older herbal uses include attempts to stop bleeding. These are records of past use, not proof of treatment safety. PFAF lists no known toxicity hazards, but gives no pet-specific assessment. The plant yields black dye from an unspecified part. Its flowers give a yellow dye when used with alum. Reports also describe burning the herb to repel flies and other insects.