Branching Principles Governing the Architecture of Cornus kousa (Cornaceae)

Abstract

The complex structure of the crown of Cornus kousa, generally five-forked in vegetative branching and two-forked in reproductive branching, is analysed quantitatively and described by two basic branching principles: decussate phyllotaxy and the resetting rule for planes of branching. Most Cornus species have opposite, decussate phyllotaxis. The leaf pair (with axillary buds) defines the branching plane of a node. Because of regular phyllotaxis, the fundamental branching pattern is that every branching plane along an axis is perpendicular to the preceding one. However, the first node of a lateral horizontal shoot always has a horizontal branching plane; we term this the resetting rule. We observed that resetting occurs when the first nodes initiated in the vertical plane are repositioned by a twisting of their first internodes. All later nodes alternate directions, i.e. show usual decussate alternation. Foliage leaf nodes usually produce three-forked branchings. When vegetative winter buds are formed, a foliar node and adjacent scale leaf node produce a five-forked branching. When reproductive winter buds with a terminal inflorescence are formed, the last foliar node and two adjacent 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 scale leaves and whose vegetative nodes are clearly separated.