Leaf epidermal structure and stomatal parameters of the genus Taxodium (Taxodiaceae)

Abstract

The linear leaves of three species in the genus Taxodium Rich., T. distichum (L.) Rich., T. ascendens Brongn., and T. mucronatum Tenore., are amphistomatic or hypostomatic. Stomatal band comprises 4-8 lines of stomata on each side of the midvein on the abaxial surfaces of the leaves. The numbers of stomata are stable on the middle parts of the abaxial surfaces of the leaves, and decrease toward both tip and base of the leaves. On the adaxial surfaces the stomatal band comprises only 1-4 lines of stomata and sometimes no stomata were observed. In the non-stomata areas the epidermal cells are oblong and parallel to the long axis of leaves, and the anticlinal walls of epidermal cells are mostly straight or some- times undulate. Epidermal cells on areas with stomata are polygonous. Stomatal apparatuses are oval, and the long axes of stomata are mostly perpendicular or oblique to the midvein. Guard cells have thickened walls, forming polar lamellae at the polar end. The stomatal density and index of T. distichum, T. ascendens and T. mucronatum exhibits significant differences. The stomatal density and index of T. distichum from different localities show no statistically significant differences. The coefficient of variability of the stomatal index is smaller than that of the stomatal density, suggesting that the stomatal index is more reliable than stomatal density when it is utilized to study the correlation between stomatal parameter and atmospheric CO2 concentration.