PlantFiles: Shepherd's Needles, Butterfly Needles, Romerillo
Bidens alba var. radiata

On one hand, this plant is great for attracting butterflies and puts on a nice show of blooms. On the other hand, it reseeds VIGOROUSLY. If cultivated, be sure to deadhead reigiously or you'll regret it in ensuing years. A tender perennial usually grown as an annual (or a weed, depending on your perspective.)

Like its relatives, this Bidens disperses seed via seeds that cling to anything brushing against the seedheads.

This is a major weed in central Florida, and many other areas of the tropics and subtropics. It really loves our sandy soils, and seedlings come up thickly as soon as the soil is disturbed. Left alone and with something to support it, it can easily reach 6 to 8 feet tall in a few months, setting thousands more seeds. I pull thousands of these every year to keep it under control.

As both noted above, it's a weed and it grows very well and almost everywhere there's moisture.
However in it's favor, during the winter months when there are not many nectar flowers for the butterflies that are around, this plant is in full bloom providing the nectar they need.
I purposly leave my yard unmowed December & January so these weeds will grow and bloom. They are a favorite of the many really small butterflies I get in my yard. I also transplanted three of them next to my Monarch area so the little butterflies would have access to them now that I am mowing again.
This plant is a Florida native.
Art

This is the most abundant native plant in my yard. I have THOUSANDS of the seedlings in all areas of full sun to deep shade. It seems that every seed that hits the ground is able to grow! I pull up as many as I can, but l leave some to grow along the back of flower beds since their year-round flowering does provide a nectar source for butterflies at times when nothing else is in bloom. The flower is an attractive, miniature "daisy" and would probably have value as an ornamental if the plant were not so prolific in self-seeding. At the back of the flower beds, it grows to about 4 ft high and blends in nicely with other plants.

Although I can't look around w/out seeing these, or step into my backyard without getting it's seeds on some clothing, I would never give up this native for anything. It's easily mowed down, so I keep a section of the yard for these alone, and guess what? When the sun is out, I cannot walk by without seeing at least 2 butterfly species, some small moth-looking things which may also be butterflies, as well as dragonflies and bees! Nothing I have can compare to the appeal that these wildflowers have to insects.
Spanish needles also contain alkaloids which are essential for the sexual maturation of young male butterflies.
Plus, this is like our only real wildflower in SoFla. I've never even come across our state wildflower! :)~