Bidens L. is a cosmopolitan genus of about 230 flowering plants in the daisy family (Asteraceae), placed in the tribe Coreopsideae alongside the closely related genus Coreopsis. The plants are commonly known as beggarticks, bur-marigolds, cobbler's pegs, and Spanish needles — names that reflect one of the genus's most distinctive traits: its seeds. Each seed (cypsela) is tipped with two to four stiff, retrorsely barbed awns that cling tenaciously to fur, feathers, and clothing, hitching rides to new habitats. It is this characteristic that gives the genus its Latin name: bi ("two") + dens ("tooth").
Members of the genus range from annual and perennial herbs to occasional shrubs and vines. Leaves are typically opposite and vary from simple to finely dissected. Flower heads are radiate or discoid, most often bearing bright yellow ray florets, though white and pinkish forms occur. The flattened, barbed seeds are a reliable identifying feature across the group.
Bidens is one of the most widely distributed plant genera on Earth. Native populations occur across the Americas, Africa, Europe, and Asia — from wetlands and stream banks to disturbed roadsides and agricultural margins. Several species have followed human activity into introduced ranges, spreading to remote island groups including the Azores, Canary Islands, Fiji, and the Cook Islands. In Western Australia, species such as B. bipinnata and B. pilosa are established aliens. In Switzerland, nine species and subspecies are documented, reflecting the genus's comfort in temperate European habitats.
The zoochorous seed-dispersal strategy is so effective that Bidens colonized remote Pacific islands including Hawaii, where, with no native land mammals to carry barbed seeds, certain lineages evolved reduced burrs and shifted toward wind dispersal — a rare reversal of evolutionary direction. Ecologically, several species serve as honey plants and as larval host plants for various Lepidoptera. Aquatic outliers also exist: B. beckii produces uniquely multifid submerged leaves adapted to life in water.
Etymology
The genus name Bidens is Latin for "two-toothed": bi ("two") + dens ("tooth"). The name refers to the pair of rigid, barbed awns that tip each seed and hook onto passing animals or clothing to achieve dispersal. This feature also gives rise to several of the genus's common names: beggarticks (seeds that beg a ride), cobbler's pegs, and stickseeds. Other vernacular names — burr marigolds and tickseed sunflowers — allude to the yellow, daisy-like flower heads that resemble sunflowers or marigolds.
Distribution
Bidens has one of the broadest natural distributions of any herbaceous genus, with native populations recorded across North America (all US regions, Canada, Central America, the Caribbean), South America (Colombia, Ecuador, Bolivia, Brazil, Chile, Argentina), Africa (Angola, Botswana, Cameroon, Ethiopia, Ghana, and many others), Europe (Great Britain, France, Germany, Austria, Greece, Scandinavia, eastern Europe), and Asia (Afghanistan, China, Bangladesh, Cambodia, East Himalaya). In Switzerland alone, nine species or subspecies are documented, ranging from native waterside plants such as B. cernua and B. tripartita to naturalized introductions like B. frondosa and B. bipinnata.
Introduced populations are particularly widespread in island systems: the Azores, Baleares, Canary Islands, Cape Verde, the Chagos Archipelago, Cook Islands, Cyprus, Fiji, Comoros, and the Gilbert Islands all host introduced Bidens. In Western Australia, B. bipinnata and B. pilosa are both established as alien taxa.
Ecology
The ecological success of Bidens is rooted in its seed-dispersal mechanism. Seeds are zoochorous: the barbed awns hook onto fur, feathers, and clothing, carrying seeds to new locations with minimal energy cost to the plant. This mechanism is efficient enough that the genus colonized remote Pacific islands far from continental source populations.
On the Hawaiian Islands, where no native land mammals existed to act as dispersal vectors, some Bidens lineages independently evolved reduced or absent burrs, shifting toward wind dispersal — a striking case of evolutionary reversal driven by ecological context. Aquatic diversity is also represented: Bidens beckii produces uniquely multifid submerged leaves adapted to freshwater habitats. Most species, however, occupy disturbed ground — roadsides, agricultural fields, stream margins, and wetland edges — where periodic disturbance keeps competition low. Nodding beggarticks (B. cernua) and hairy beggarticks function as honey plants, attracting pollinators, while many species serve as larval host plants for Lepidoptera.
Cultivation
Bidens species suited to garden cultivation prefer full sun and will not tolerate shade. They are adaptable to a wide range of soil textures — light sandy soils to heavy clay — provided moisture is retained. Moderately fertile, well-drained but consistently moist conditions produce the best growth. Hardiness varies by species; ornamental selections generally perform in USDA zones 7–10, surviving short periods down to around -5 to -10°C. In warmer climates many species self-sow freely. Bidens ferulifolia and related ornamental taxa are widely grown as summer bedding and container plants for their continuous display of yellow daisy flowers.
Propagation
Two propagation routes are commonly used for Bidens. Seed is the primary method: surface-sow in a greenhouse or cold frame in spring, keeping the medium consistently moist. Once seedlings are large enough to handle, pot them on individually and harden off before planting out in late spring after frost risk has passed. Most species germinate readily and can also be direct-sown outdoors once conditions are warm. Division is suitable for perennial forms: lift and divide established clumps in spring, replanting divisions promptly.
Cultural Uses
Across various cultures, Bidens species have been valued as food and medicine. The leaves of at least some species are used as a tea substitute, and dried leaves are nutritionally dense — analyses of certain species record approximately 295 kcal/100 g, with exceptional calcium content (around 1,721 mg/100 g) and a high protein fraction (roughly 24.5 g/100 g). Native Hawaiians prepared a traditional herbal tea from the leaves of endemic Hawaiian Bidens species. Nodding and hairy beggarticks also function as honey plants, supporting apiculture in regions where they occur in abundance.
Taxonomy Notes
Bidens was formally described by Carl Linnaeus and is placed in family Asteraceae, tribe Coreopsideae. The genus is most closely allied to Coreopsis, and phylogenetic analyses have shown that neither genus is monophyletic as traditionally circumscribed, indicating that taxonomic revision is ongoing. Species estimates vary: Wikipedia cites roughly 230 species; SEINet references approximately 200 cosmopolitan species; GBIF records 434 descendant taxa including synonyms and infraspecific names. The growth form spans annuals, perennials, shrubs, and vines. In Switzerland, Info Flora recognises nine taxa at species and subspecies rank.
