Abstract
Evolutionary radiations in growth forms represented key events in the rise of early angiosperm success. However, understanding the directions of early angiosperm growth lability and the traits determining growth form innovations remain unclear. Lianescence appears to represent an early evolved direction of early angiosperm growth form experimentation, owing to occurrence of lianas in the extant, early diverging clade Austrobaileyales. Here we examine biomechanical and hydraulic ecophysiology of Schisandra glabra (Schisandraceae) in the context of its habitat and xylem form-function to test hypotheses about the functional performance of basal angiosperm lianescence. We found that S. glabra evolved much higher twist-bend flexibility, greater hydraulic efficiency, and capacity as compared to a nonclimbing relative from similar habitats, Illicium floridanum. However, lianescence was not associated with increased leaf photosynthetic capacity, drought tolerance, or a more cheaply constructed body plan. We found that a small number of stem structural shifts, involving primarily increases in cell sizes of vessels, tracheids, and the proportions of living tissues, were involved in exploration of the liana habit in the Austrobaileyales. Our results suggest that evolution of early angiosperm lianescence was potentially a relatively facile transition involving relatively small changes in xylem structure to achieve large change in stem biomechanical performance.