Approximately 200 species are classified as fleabanes, most of which are annuals or biennials, though a few are evergreens. The plants are well-branched and may feature flowers in a variety of colors when in bloom. Most varieties of fleabane exhibit flower heads that are composed of both a central, disk flower consisting of numerous tightly packed flowers that at first appear to be a single entity and ray flowers, which are the elongated petals evenly spaced around the periphery of the disk flower. Ray flowers are sterile but are attractive to many pollinating insects and are absent in a few fleabane species. Since the disk flower is the nectar- and pollen-rich section of the plant, it is an essential part of all fleabane varieties.