ABSTRACT
Bidens radiata (Compositae) Thuill. is an annual, herbaceous plant, widespread in fens and wet ditches; it is about 8 to 60 cm high. 1 Its shoots are erect and glabrous; leaves, opposite and decussate, are often divided into 3 to 5 parts. Capitula, erect on peduncles, are grouped together in a corymb. Yellow florets, all with stamens and pistil, develop in the axil of brown striped membraneous bracts. Foliaceous unequal-shaped bracts constitute the external involucre. The fruit is an achene of 4 to 5 mm length surmounted by 2 teeth.
