Spanish Needles
Bidens pilosa
A head of mature seeds, ready to be dispersed, of Spanish Needles. Photographed in a small corn field near Eldoret, Rift Valley Province, Kenya. 14 October 2010.
Two barbed spurs at the corners of the flattened seeds have served to carry
this weedy annual from its original home in tropical America to most places in
the tropics and subtropics around the World. In the photo at left about 30
mature seeds each represent what was a single small flower or floret. The
florets and thus the seeds are grouped together in a compact head. The florets
were of two types in the composite head: rays displaying a white strap-like
petal, and yellow disc florets with five, very short petals. The size and
number of the white rays vary considerably between populations of Bidens pilosa;
sometimes no rays are apparent. In Kenya Spanish Needles is an important weed
in farms and gardens where it has a major detrimental impact on crop yields, but they are a source of
nectar for butterflies. A Chief at Kakamega, below.
