Bidens is a genus of flower in the daisy family, Asteraceae. It has about 200 species covering a wide geographical range, with common names including beggarticks, burr-marigolds, stickseeds, and tickseed sunflowers. These names reference the plants' method of dispersal, burrs that stick to clothing or fur, allowing them to be carried over long distances. The burrs are thought to resemble ticks and could be carried over long distances on a beggar's clothing. Bidens plants growing in limited areas, especially those on islands, often have reduced burrs and have developed features promoting wind dispersal of seeds.
These plants are fairly easy to grow in a garden, and many people enjoy their appearance, though they are also often considered weeds. The plants resemble daisies, with bright yellow or white flowers. Bidens are usually grown in containers, often as a filler plant. It is important to keep the soil well moisturized and fertilized, and to immediately cut off dead flowers to promote abundant blooms. The plants tolerate heat moderately and prefer full sunlight.
Bidens species are also used in Traditional Chinese Medicine (TCM) to treat dysentery, poisonous bites, and skin conditions. B. pilosa, or Spanish needle, and B. tripartita, or three-lobed beggarticks, are sometimes used as food, with the shoots and leaves cooked and eaten as vegetables. B. pilosa is also used as a honey plant, along with B. cernua or the nodding burr-marigold.
In Hawaii, Bidens are called koko'olau and are sometimes used as a tea. Many species have a very limited range and are threatened with extinction. These include B. amplectens or the wai'anae koko'olau, found only on the island of Oahu, and B. molokaiensis or the Moloka'i beggarticks, found only on the island of Moloka'i. Additional threatened species of Hawaii are B. cosmoides or the cosmosflower beggarticks, endemic to Kauai, and B. conjuncta or bog beggarticks, which grows only in western Maui. All of these species are threatened by habitat loss, particularly caused by brushfires and invasive weeds.
Some other Bidens species with very limited ranges are B. mannii, endemic to Cameroon, and B. simplicifolia, endemic to Ecuador. Some species of Bidens, on the other hand, have become invasive when introduced to new environments. B. frondosa, commonly called devil's beggarticks or pitchfork weed, is classified as an invasive alien plant by the European and Mediterranean Plant Protection Organization (EPPO) and as an environmental weed in New Zealand.
