Systematic Position Of Tetracentron (Trochodendraceae) Based On Morphological Data

Tetracentron sinense Oliv. is a monotypie species in Tetracentron endemic toeastern Asia. The systematic position of Tetracentron has been disputed for a long time.Many features of Tetracentron in China were described in the present paper. Weattempted to supply some new features on the determination of the systematic positionof Trochodendraceae.1 AnatomyRoot: In Tetracentron the primary structure of root is consisted of epidermis, cortex,vascular cylinder, the secondary structure is similar to other dicotyledonous.Stem: The vascular bundles of the primary structure in stem are ring arranged, andthe rays in the secondary wood are homocellular. Among the cortex cells, there aremany large idioblasts. The node is trilacunar and 3-tracedLeaf: The vascular bundles of the petiole retain an opening in base, combine acylinder in the middle, and separate into 5～7 bundles. The petiole contains largeidioblasts. The stomata leaves are anomocytic type.Flower: On the receptacle, there are one bract, 4 perianth, 4 stamens and 4 carpels.The perianth are without vascular bundle, filament with one and with 5 vascular bundlesin each carpel. Large idioblasts distribute in every flower organs.2 The discovery of vessel and variation of perforation plate in the stemThere are vessels in the secondary wood of Tetracentron sinensis Oliv., The vesselsare as narrow and as long or slightly shorter than the tracheids and generally with 1 to 3very long, or sometimes shorter, and oblique end-wall perforation plates as well as onthe lateral-wall. The perforation plates of the vessels include scalariform and reticulate-scalariform types. The perforation pits are with or without pit membrane remnants.3. Morphogenesis of FlowersIn Tetracentron of the basal eudicot family Trochodendraceae, the flowerprimordium, together with the much retarded floral subtending bract primordium appearto form a common primordium. The four tepals and the four stamens are initiated infour distinct alternating pairs, the first tepal pair is in transverse position. The four carpels arise in a whorl and alternate with the stamens. This developmental patternsupports the interpretation of the flower as dimerous in the perianth and androecium,but tetramerous in the gynoecium. There is a relatively long temporal gap between theinitiation of the stamens and the carpels. The carpel primordia are then squeezed intothe narrow gaps between the four stamens.4. Systematic positionAccording to the characters of Morphological foral organogenesis et.al, ofTetracentron sinense, we considered that Tetracentron might be a primary taxon inwoody dicotyledons and the Trochodendraceae might occupy the basic position in theeudicots.