Most Asterids show a combination of derived floral characteristics. Fused petals, reduced numbers of stamens attached to the corolla, and zygomorphic flowers are all commonly encountered within the Asterids. However, the only morphological synapomorphy that all Asterids share is the presence of a single integument layer on the embryo, which is useless as a field mark. As currently recognized, the Asterids contain some plants formerly classified as Rosids or Dilleniids. The family Asteraceae has perhaps the most modified inflorescences of any angiosperm; the superficial "flowers" of many Asteraceae are actually a disk of many crowded, radially symmetric flowers, surrounded by a ring of ligulate flowers that each resemble one petal.
The orders of Asterids have been subgrouped by the APG (1998) and others into groups known as Euasterid I and Euasterid II, with the orders Cornales and Ericales branching before divergence of those clades. Boraginaceae is still unplaced to order within the Asterid I clade.
More information coming soon...