Morphology, Growth, and Vasculature of the Sympodial Rhizome of Smilacina racemosa (Liliaceae)

Abstract

A time-course study of shoot development in Smilacina racemosa was combined with an analysis of the vascular anatomy to investigate how adjacent sympodial units in the perennial rhizome are structurally related to one another. Organogenesis is seasonal and occurs over a period of 20 mo; leaves and flowers are preformed in miniature 8-12 mo before they fully expand. One lateral bud on the horizontal rhizome is initiated eccentric of the normal plane of distichy toward the lower side of the stem and develops as the renewal shoot. The vascular connection between the renewal shoot and the parent axis is complete; all but 2% of the central bundles of the parent axis directly enter or branch into the renewal shoot. Two features contribute to the completeness of the connection: (1) increased anastomoses of vascular bundles within the branch junction, and (2) the development of special girdling bundles that attach circumferentially to the parent axis. The vascular supply of dormant lateral buds is incomplete; roots attach only to the peripheral region of the central cylinder. The complete connection between adjacent sympodial units allows for a high level of physiological integration within the rhizome, while the restricted circumferential attachment of root traces may significantly influence the hydraulic pathway through the plant.