Branching principles governing the architecture of Cornus kousa (Cornaceae)

The complex structure of the crown of Cornus kausa, generally five-forked i n Vegetative branching and two-forked in reproductive branching, is analyse d quantitatively and described by two basic branching principles: decussate phyllotaxy and the resetting rule for planes of branching. Most Cornus spe cies have opposite, decussate phyllotaxis. The leaf pair (with axillary bud s) defines the branching plane of a node. Because of regular phyllotaxis, t he fundamental branching pattern is that every branching plane along an axi s is perpendicular to the preceding one. However, the first node of a later al horizontal shoot always has a horizontal branching plane; we term this t he resetting rule. We observed that resetting occurs when the first nodes i nitiated in the vertical plane are repositioned by a twisting of their firs t internodes. All later nodes alternate directions, i.e. show usual decussa te alternation. Foliage leaf nodes usually produce three-forked branchings. When vegetative winter buds are formed, a foliar node and adjacent scale l eaf node produce a five-forked branching. When reproductive winter buds wit h a terminal inflorescence are formed, the last foliar node and two adjacen t scale leaf nodes can produce a variety of branchings but usually produce an equal two-forked branching. To understand better the architecture in C. kousa, we contrast it with C. capitata which does not produce buds with sca le leaves and whose vegetative nodes are clearly separated. (C) 1999 Annals of Botany Company.