Vessel diameters in roots versus stems of tropical lianas and other growth forms
For trees and shrubs it is well known that vessels tend to be wider in roots than in stems. It is also well known that vines have narrow stems with wide vessels, but roots of vines have been little studied. It was hypothesized that the evolution of the vine habit involved greater changes in stems than in terrestrial roots, and thus vessels in stems of vines would tend to be as wide, or wider, than in roots. Radial vessel diameters were compared in roots versus stems of 62 taxa from 20 families of plants based upon collections made at Barro Colorado Island (BCI) in Panama and Fairchild Tropical Garden (FTG) in Miami, FL, USA. As expected, for Fabaceae trees + shrubs, mean and maximum vessel diameters were significantly greater in roots than in stems. The reverse was true for Fabaceae lianas (woody vines), where vessel diameters were significantly greater in stems. When comparing stems of all climbing species (n = 51) to non-climbing species (n = 11), the climbing species had significantly greater mean and maximum vessel diameters. In contrast, for root vessels differences between growth forms were not statistically significant.