Xylem hydraulic characteristics, water relations and wood anatomy of the resurrection plant Myrothamnus flabellifolius Welw.

Myrothamnus flabellifolius Welw. is a desiccation-tolerant ('resurrection') plant with a woody stem. Xylem Vessels are narrow (14 mu m mean diameter) and perforation plates are reticulate. This leads to specific and leaf specific hydraulic conductivities that are amongst the lowest recorded for angiosperms (k(s) 0.87 kg m(-1) MPa-1 s(-1); k(1) 3.28 x 10(-5) kg m(-1) MPa-1 s(-1), stem diameter 3 mm). Hydraulic conductivities decrease with increasing pressure gradient. Transpiration rates in well watered plants were moderate to low, generating xylem water potentials of -1 to -2 MPa. Acoustic emissions indicated extensive cavitation events that were initiated at xylem water potentials of -2 to -3 MPa. The desiccation-tolerant nature of the tissue permits this species to survive this interruption of the water supply. On rewatering the roots pressures that were developed were low (24 kPa). However capillary forces were demonstrated to be adequate to account for the refilling of xylem Vessels and re-establishment of hydraulic continuity even when water was under a tension of -8 kPa. During dehydration and rehydration cycles stems showed considerable shrinking and swelling. Unusual knob-like structures of unknown chemical composition were observed on the outer surface of xylem Vessels. These may be related to the ability of the stem to withstand the mechanical stresses associated with this shrinkage and swelling. (C) 1998 Annals of Botany Company.