The rosids are divided into 17 orders. These orders together make up about 140 families. The rosids and the asterids are by far the largest clades in the eudicots.
Rosids are very basic flowering plants. Fossil rosids are known from the Cretaceous period. Molecular clock estimates indicate that the rosids originated in the Aptian or Albian stages of the Cretaceous, between 125 and 99.6 million years ago (mya).[3]
Three different definitions of the rosids are in use. Some authors include the order Saxifragales in the rosids. Others exclude it.
↑Scotland, Robert W.; Wortley, Alexandra H. (2003). "How many species of seed plants are there?". Taxon. 52 (1): 101–104. doi:10.2307/3647306. JSTOR3647306.