Five evergreen subtropical tree species growing under identical environmental conditions were investigated to
establish which hydraulic properties are genotypically rigid and which show phenotypic plasticity. Maximum
xylem-specific conductivity (ks) correlated well with the anatomical characteristics (conduit diameter and density)
for the four angiosperms Tecomaria capensis, Trichilia dregeana, Cinnamomum camphora and Barringtonia
racemosa; the anatomy of the gymnosperm Podocarpus latifolius was not assessed. Huber values (functional xylem
cross-sectional area [ratio ] leaf area) varied inversely with ks among species. Maximum leaf-specific conductivity was
similar in the five unrelated species. Vulnerability of xylem to cavitation differed between species, as did the
relationship between transpiration and water potential. Models of these parameters and isolated midday readings
confirm that these trees operate at similar maximum leaf-specific conductivity (kl) values. The data are consistent
with the hypothesis that conductivity characteristics (kl, ks) are influenced by environment, whereas vulnerability
to cavitation is genetically determined.