Shepherd's needles

Appearance

''Bidens alba'' is a vascular plant. It has a similar root and stem system to others in the dicot family ''Asteraceae''. After germinating, the roots progress into a tap root that grows vertically in the ground. The primary tissue of the apical meristems increases the length of the plant and the secondary roots of the lateral meristems give rise to the width. ''B. alba'' grows to a height of approximately five feet tall.

The stem of ''B. alba'' plant emerges from the taproot, yet the bent stem at the base also has the ability to grow into roots at the lower nodes. Stems are mostly hairless and green to purplish in color. The vascular bundle provides nutrients throughout the plant, with the phloem transporting water from the roots and the xylem obtaining food from the leaves.

''Bidens alba'' leaves, which are simple on the opposite side and compound on the underneath, are 2–10 centimetres long and 1.0–3.5 cm wide. The underside leaf is hairy, and has toothed edges. The leaves may be lobed, depending on the species. Some have teeth and some do not; each node produces two leaves along the stem.

Each flowering head of ''B. alba'', which is small, appears in radial symmetry. The flowers on this plant are depicted as daisy-like due to the larger white petals and the very small yellow flowers which are located at the end of the branches. Colors of the flower-heads of ''Bidens alba'' vary depending on the subspecies; some ''B. alba'' have yellow, tubular central blossoms and others may have flower-heads with white or cream petals ; eventually they form black linear seeds, yielding approximately 1200 seeds per plant.

Naming

''Bidens'' means two- toothed, describing the two projections found at the top of the seeds, and ''alba'' refers to the white ray florets.

Distribution

This plant is found in tropical and subtropical regions of North America, Asia, South America, and Africa, situated in gardens, road sides, farm fields and disturbed sites. ''B. alba'' is an annual or short-lived perennial, which is considered an weed in the United States.

Uses

People in South Africa, Zulus and Indians consume the fresh or dried leaves by boiling them. Young leaves of ''B. alba'' may also be eaten as a salad.