An Illustrated Flora of the Northern United States, Canada and the British Possessions/Dicotyledones

Sub-class 1. Dicotylédones.

Embryo of the seed with two cotyledons (in a few genera one only, as in Cyclamen, Pinguicula and some species of Ranunculaceae and Capnoides), the first leaves of the germinating plantlet opposite. Stem exogenous, of pith, wood and bark (endogenous in structure in Nymphaeaceae), the wood in one or more layers surrounding the pith, traversed by medullary rays and covered by the bark. Leaves usually pinnately or palmately veined, the veinlets forming a network. Parts of the flower rarely in 3's or 6's.

Dicotyledonous plants are first definitely known in Cretaceous time. They constitute between two-thirds and three-fourths of the living angiospermous flora.

Series 1. Choripetalae. Petals separate and distinct from each other, or wanting
Series 2. Gamopetalae. Petals wholly or partly united, rarely separate or wanting