Epidermal Structures And Stomatal Parameters Of Taxodiaceae

The objective of the present work is to establish a frame of reference in epidermal structures of Taxodiaceae, and to determine quantitatively the reliable stomatal parameter (density or index) as a CO₂ indicator in genera Sequoia, Metasequoa, Taxodium and Glyptostrobus based on statistical analysis, and to reveal the affinity of speciemen from the Eocene of Yilan, Heilongjiang Province, NE China and from the Miocene of Luhe, Yunnan Province, South China.The deciduous genera in Taxodiaceae commonly have papyraceous cuticle which is easily distinguished from coriaceous cuticle of evergreen leaves. Epidermal cells of stomata-free area are oblong and parallel to the long axis of leaves. The anticlinal walls of epidermal cells are mostly straight in most genera, sometimes slightly undulate in Taxodium and Cunninghamia, and obviously undulate in Metasequoia. Epidermal cells on stomatal areas are sometimes polygonous. Pits can be clearly seen in the walls of epidermal cells. Leaves are amphistomatic or hypostomatic. Stomata are located on each side of the mid-vein. The numbers of stomata on the abaxial surfaces are generally more than or sometimes the same as those on the adaxial surfaces in linear and lanceolate leaves. The distribution of stomata is generally more uniform on the abaxial surface of linear and lanceolate leaves, and the mid-part of the abaxial surface yields the least variation in stomatal distribution. The numbers of stomata on the adaxial surfaces are more than or sometimes the same as those on the abaxial surfaces in subulate leaves of Taxodiaceae. Stomatal apparatus are oval, and the long axes of stomata are perpendicular or oblique to the midvein of the leaves in Taxodium, and oblique to the midvein of the leaves in Cryptomeria, mostly parallel to the midvein of the leaves in other genera of Taxodiaceae. Guard cells have thickened walls, especially on outer margins. The thickened walls of guard cells form polar lamellae that produce protruding and curved ends at the two poles of the stomata. Commonly the stomata have 4 to 7 subsidiary cells.The Mest of stomatal parameters of Glyptostrobus pensilis from Guangzhou and Hangzhou indicate the variation of stomatal parameters of linear leaves is smaller than that of linear-subulate leaves. The variation of stomatal index of the abaxial surfaces is smaller than that of the index of the adaxial surface, and also is smaller than that of the density of the abaxial and adaxial surfaces in linear-subulate leaves according to the Mest. When studying the correlation between stomatal parameters of Glyptostrobus and atmospheric CO₂ concentrations, the stomatal parameters of linear leaves are firstly chosen, and the stomatal index is more useful than stomatal density. The intra-individual variation of stomatal index is smaller than that of the density by comparing the coefficient of variability(CV) of stomatal density with the CV of index in genera Sequoia, Metasequoa, Taxodium and Glyptostrobus. Thus, even if stomatal density and stomatal index show similar responses for a given species, stomatal index should yield more accurate CO₂ estimates in genera of Sequoia, Taxodium, Metasequoia and Glyptostrobus.Foliage shoots of Sequoia are reported form the Eocene of Yilan, Heilongjiang Province, NE China and from the Miocene of Liihe, Yunnan Province, South China. The leaves from both Yilan and Liihe are linear in shape, coriaceous in texture and the leaf base is decurrent and attached obliquely to the axis of shoots. The walls of epidermal cells are straight, and the long axis of stomata is mostly parallel to mid-vein in present specimens. It suggests that the new specimens are assigned to Sequoia rather than to similar genera of Metasequoia, Taxodium and Glyptostrobus. The presence of Sequoia during the Eocene in Yilan and Miocene in Luhe shows the detailed cuticle, which may provides valuable information on cellular structures and on the palaeoclimate.