A large subclass of the class Magnoliopsida (dicotyledons) of the division Magnoliophyta (Angiospermae), the flowering plants, consisting of 13 orders, 78 families, and nearly 25,000 species. The subclass is morphologically ill-defined, but most of the orders and species have the carpels united to form a compound pistil. The petals are either separate or joined into a sympetalous corolla, but the sympetalous members generally lack the advanced features of the subclass Asteridae. That is, they do not have a single set of stamens alternate with the corolla lobes, ovules with a massive single integument, or a reduced nucellus. The stamens, when numerous, are initiated in centrifugal sequence. Many of the species have numerous ovules on parietal placentas; that is, the placentas are borne along the walls of an ovary which is usually with a single chamber. Many have various chemical repellents and are often tanniferous. There are mustard oils or iridoid compounds in some orders, but mostly they are poor in alkaloids and without betalains.