Unusual cells are reported for mature wood and branchwood of Tetracentron. They are thin-walled tracheids, rectangular in cross section, much shorter and a little wider than normal tracheids, and arranged in conspicuous radial files. They have crowded, alternate, circular to elliptical bordered pits in the tangential walls. Their radial walls are devoid of pils, except in crossfield areas and very rarely in limited areas of the walls touching normal tracheids. In contrast, normal tracheids have scalariform and circular pits confined to the radial walls. In earlier reports the unusual tracheids have been observed in twigs and roots, but in our materials they are a regular feature of mature wood samples as well. Their possible functional and phylogenetic significance is discussed.