The morphological variations of inflorescences are very complex, mainly manifested as the length of the inflorescence axis, whether it branches or not, the presence or absence of flower stalks, and the order of flower opening, etc. According to the order of flower opening on the inflorescence axis, inflorescences can generally be divided into two categories: limited inflorescences and unlimited inflorescences.
Limited inflorescences, also known as cyme inflorescences, have the flower primordia formed at the top of the main inflorescence axis first and flowering earliest, so the growth of the inflorescence axis is inhibited and it no longer continues to grow, while new flower primordia are formed on the side branches successively. However, the side branches also flower from the top to the bottom. Because of this, limited inflorescences have few branches and a relatively small number of flowers. The order of flowering is usually that the flowers at the top or in the middle open first, and then the side branches open from the inside to the outside. According to the different development of the main axis and side branches, limited inflorescences can be divided into: unilobate cyme inflorescences, bilobate cyme inflorescences, multilobate cyme inflorescences, and whorled cyme inflorescences.
Unlimited inflorescences, also known as racemose inflorescences, have inflorescence meristems that can maintain vigorous regenerative capacity and continuously differentiate new flower primordia at the peripheral zone of the inflorescence meristem, or repeatedly produce side branches and continuously differentiate flower primordia on the side branches. The flowers of such inflorescences are usually opened from the lower part of the inflorescence axis first, then gradually upward, and the inflorescence axis continues to grow, or the flowers are opened from the edge to the center. Unlimited inflorescences can be further divided into racemose inflorescences, pyramidal inflorescences, spike inflorescences, compound spike inflorescences, spike-like inflorescences, cyme inflorescences, umbel inflorescences, corymb inflorescences, compound umbel inflorescences, compound corymb inflorescences, capit inflorescences, and concealed capit inflorescences.
In addition, some plants have a mixture of unlimited and limited inflorescences, so that the inflorescence axis can grow indefinitely, but the side branches become limited inflorescences; or the growth of the inflorescence axis at the top stops quickly, while the side branches can continue to grow for a longer period of time.
People's understanding of the evolution of inflorescences is very limited. At present, the widely accepted view is that solitary flowers are the most primitive type in the evolution of angiosperms.