Purple Thistle - Cirsium horridulum

Purple thistle (aka yellow thistle) (Cirsium horridulum) is an annual or biennial herbaceous "weed" that occurs throughout Florida and in much of the eastern seaboard - though it is classified as a state-endangered species in much of the northeast.  This is a plant of roadsides and other disturbed habitats, and thrives across a wide variety of soil types in full to partly sunny conditions.
As its Latin name implies, it is a robust, wickedly spined plant. The broad rosette of basal leaves may be several feet across.  The sharply toothed leaves are armed with stout spines at the end of each tooth.  This, and the milky sap it produces, protects it from herbivorous wildlife; but, like so many times in nature, the caterpillars of the little metalmark butterfly are uniquely adapted to feed on it.  This tiny, but beautiful butterfly, is featured at the top of this post, nectaring on an aster flower.
A husky flower stalk arises from the center of the rosette by summer.  It too is spiny and eventually reaches a height of about 3-4 feet. Large spiny flower heads form at the end of each stem - and along a few side stems near the top.  These open to large and very showy lavender flowers that are exceptional nectar sources for all types of pollinators.
Though few wildflowers are better nectar sources, purple thistle is impossible to control in a landscape setting. Once established, it often there to stay - producing new plants from underground suckers and from the copious fluffy seed that gets carried everywhere by the wind. I do not recommend it for landscapes, but it is a hub of activity if you are out looking for butterflies, bees, and the like.  When I am hiking or driving and see a stand of purple thistle, I always try to stop if I have my camera with me. You never know what you might see nectaring from it.