They are surrounded on the perimeter by the infertile ray florets which have a showy petal attatched. If you look closely at these petals they are actually several petals fused together. There are however, several exceptions to this pattern. In the silphiums (Cup Plant, Compass Plant etc) for example the ray florets are fertile and the disc florets sterile. In dandelions (and native relatives like Krigia) there are no distinctions between disc and ray florets, they have the same structure and are all fertile.
Name Games: The problem with common names is that one species may have many common names or one common name may be used to for more than one species. When talking about frost aster this week we are talking about Aster pilosus. Another common name for Aster pilosus is heath aster but most sources use 'heath aster' to refer to Aster ericoides. As if to keep things fun and interesting botanists have decided to split up the genus Aster and there is now another genus, Symphyotricum. Consequently a newer name for A. pilosus is Symphyotricum pilosum.
Description: Like so many asters and daisies, A. pilosus has white ray florets and yellow disc florets. The bracts (see figure above) that surround the base of each compound flower lack any hairiness (pubescence) and have little micro spines on them and at their tips. Meanwhile Aster ericoides, the other plant with the same common name, has hairy bracts with very tiny whitish spines. A. ericoides' leaves are also smaller and more blunt than those of A. pilosus. A. pilosus can also be recognized because it has a dense circular cluster of leaves at the base of the plant (a basal rosette) while the leaves on the stems are smaller, narrower, and more widely spaced.
Habitat/ Cultivation: There are a couple subspecies of A. pilosus with slightly different habitat preferences. These preferences range from rocky or sandy alkaline soils to limestone outcrops and fens as well as disturbed fields and roadsides. Almost any abandoned lot in Milwaukee is likely to have frost aster growing on it, especially if it is gravelly or has generally poor soil. Frost aster is an easy plant to grow, so easy that it is often considered a little "weedy". It's a great plant to grow if you have a lot of room and don't mind a lot of volunteer seedlings popping up. Frost aster needs full sun to partial shade.
Ecological Value: Because of its "weedy" nature it is great at colonizing disturbed and "waste places". It protects soil from erosion and provides food for wildlife where more sensitive plants cannot yet grow. It is called frost aster because it continues blooming late into the fall, unfazed by frosty nights. Because of its late blooms it is extremely valuable to pollen and nectar eating insects which don't have as many food options in the late fall.
Native Range: A. pilosus is found throughout Wisconsin and every US state and Canadian province east of the Rocky Mountains.
