Morphological studies on the genusClematis Linn

Abstract

While the axes of branched axillary inflorescences seen in most species ofClematis show fundamentally the same features in nodal vasculature as the vegetative stems, those of simple axillary inflorescences, having only a pair of opposite sterile bracts at specific positions, exhibit an exclusive feature in nodal vasculature because they have entirely lost lateral branches or buds in the bract axils. Noticeably, at the nodal level of the axis of the simple inflorescence ofC. japonica andC. Williamsii, trace bundles to the missing lateral branches are formed and extend unaltered beyond the node. Thus, in these two species stelar bundles in the inflorescence axis generally increase in number upwardly from six to eight or more through the node with sterile bracts. On the basis of both anatomical and morphological data, a probable evolutionary trend in floral shoots with simple axillary inflorescences is proposed. The type of floral shoot ofC. tosaensis bearing simple, scale-subtended and basally fascicled inflorescences is the most primitive and constitutes an initial phase of evolution, and progressive changes in a kind of inflorescence-subtending leaves as well as in the shape and position of the sterile bracts resulting in the type of floral shoot ofC. japonica and further in that ofC. obvallata. A floral shoot ofC. Williamsii follows another line of evolution from an ancestral type similar to that ofC. tosaensis.