Epidermal structure of giant redwood and its comparison with those of coast redwood and dawn redwood

Giant redwood (Sequoiadendron gigantean), the only living species of the genus, is endemic to the United States.The leaves of giant redwood are scale-subulate and amphistomatic.The epidermal cells are rectangular within the non-stomatal areas, and the long axis of epidermal cells is parallel to that of leaves.Two similar stomatal bands distribute on each of the abaxial and adaxial surfaces of leaves.Most stomatal bands comprise 2-5 lines of stomata, and the widest part of stomatal band is located on the middle part of the leaf.The number of stomata on the adaxial surfaces is more than that on the abaxial surfaces in the top part of leaf, but the number of stomata on the adaxial surfaces is less than that on the abaxial surfaces in the base part of leaf.The number of stomata on the adaxial surfaces is about the same as that on the abaxial surfaces in the middle part of leaf.Stomata and pores are elliptic.The long axes of most stomata are parallel to those of leaves.Guard cells have thick walls, especially on the outer margins.The subsidiary cells are different from the epidermal cells in morphological features and the angle of insertion on the view of scanning electron microscopy (SEM), so the subsidiary cells show a very distinctive oval or round appearance on the inner surface of cuticle.Compared with the epidermal structures among giant redwood, coast redwood (Sequoia sempervirens, the neighbor species of giant redwood) and dawn redwood (Metasequoia glyptostroboides, native species of China), the anticlinal walls of epidermal cells are mostly straight in giant redwood and coast redwood, but they are obviously undulate in dawn redwood.The size of epidermal cells in giant redwood is similar to that in dawn redwood, and it is apparently smaller than that in coast redwood.Most stomata locate on the abaxial surfaces of leaves in dawn redwood, and they locate on both the abaxial and adaxial surfaces of leaves in giant redwood.As the stomatal distribution, some leaves in coast redwood are similar to those in dawn redwood or in giant redwood.The stomatal morphology and size in giant redwood are more similar to those in coast redwood than to those in dawn redwood.