Stem and root wood anatomy of the shrub Phlomis fruticosa (Labiatae)

Wood from the stems and roots of the malacophyllous Mediterranean drought semi-deciduous species Phlomis fruticosa was studied. The stem is diffuse-porous with narrow vessels. Though narrow vessels impose high conducting resistance, they are less vulnerable to cavitations, thus providing safety during summer drought and winter freezing. The geographical distribution of the plant (up to 1400 m altitude) may be relevant to the occurrence of narrow stem vessels, which provide high resistance to cavitations from low temperatures during winter. Vessel grouping in the stem adds to the safety against cavitations. Root vessels are mostly solitary and have almost double the diameter of stem vessels. Diffuse-porosity, the presence of narrow vessels in stems and the values of vulnerability and mesomorphy indices, are adaptations to the two stresses imposed by the Mediterranean climate, i.e. summer drought and winter cold.