Bidens bipinnata aka Spanish Needles

Bidens bipinnata, or Spanish needles, belongs to the daisy family. It grows as an upright annual with fine-cut leaves. Sources differ on where this plant first grew. PFAF lists eastern Asia and eastern North America as native. Useful Tropical Plants suggests an eastern Asian origin. It now grows across many warm and temperate regions. It occurs in woods, fields, roadsides, and disturbed ground.

Garden accounts place its height around 1–4 feet [0.3–1.2 m]. Useful Tropical Plants gives a usual maximum of 5 feet [1.5 m]. Some plants reach about 8 feet [2.5 m]. The upright stems have four angles and raised ridges. Some plants branch thickly, while others have fewer branches. Opposite leaves divide twice into fine sections, called bipinnate leaves. This leaf shape gives the plant a light, fine texture.

Small flower heads have yellow central florets and few outer rays. Some heads have no rays at all. Each head spans about 0.4–0.8 inches [0.01–0.02 m]. PFAF lists flowering from September to October, with seeds ripening in October. Insects pollinate the flowers, which draw bees and butterflies. Small birds also feed on the seeds. The narrow, black fruits have four angles and barbed awns. These hooks catch on fur and clothes, spreading seeds elsewhere.

Grow it in full sun and soil that holds moisture. It accepts sand, loam, and clay of moderate fertility. It also tolerates mildly acid, neutral, and mildly alkaline soil. PFAF says established plants can cope with drought. Moist soil remains its stated preference for growth. PFAF lists USDA hardiness zones 4–11 for this annual. Sow seeds in place in mid- to late spring. Cover them with only a thin layer of soil. Its fast growth and flowers can support wildlife in beds. Yet its wide spread as a weed warrants care. Clinging fruits can also make mature plants awkward to handle.

People cook the leaves and young shoots as greens. They also use them to add flavour to food. The flowering tops provide material for tea. Sources describe the taste in different ways, including bitter and sharp. PFAF warns that the barbed seeds pose an ingestion hazard. Useful Tropical Plants lists no known hazards. Neither statement establishes safety for pets. Records also describe use in folk medicine, including throat remedies. These reports do not establish safe or effective treatment.