The Monandreae have been subdivided into twenty-eight tribes, the characters of which are based on the structure of the anther and pollinia, the nature of the inflorescence, whether terminal or lateral, the vernation of the leaf and the presence or absence of a joint between blade and sheath, and the nature of the stem.
In botany the word is used of the praefloration or folded arrangement of the petals in a flower before expansion in the summer, contrasted with "vernation" of leaves which unfold in the spring.
The arrangement of the leaves in the bud is termed vernation or prefoliation.
In considering vernation we must take into account both the manner in which each individual leaf is folded and also the arrangement of the leaves in relation to each other.
The leaves in the bud are either placed simply in apposition, as in the mistletoe, or they are folded or rolled up longitudinally or laterally, giving rise to different kinds of vernation, as delineated in figs.
The leaves have a definite relation to each other in the bud, being either opposite, alternate or verticillate; and thus different kinds of vernation are produced.
The scales of a bud sometimes exhibit one kind of vernation and the leaves another.
The latter terms are applied to the flower-bud in the same way as vernation is to the leaf-bud, and distinctive names have been given to the different arrangements exhibited, both by the leaves individually and in their relations to each other.
Sometimes they are nearly in a circle at the same level, remaining flat or only slightly convex externally, and placed so as to touch each other by their edges, thus giving rise to valvate vernation.
- Circinate vernation.