Most 19th and early 20th century works treated Chamaecyparis Spach as an infrageneric taxon within Cupressus L. (Cupressaceae). In recent works Cupressus and Chamaecyparis are recognized as separate genera on the basis of a single constant character: the presence of vermiform (a.k.a. trabeculate) thickenings on the pits of leaf transfusion tracheids in Cupressus and the absence of such thickenings in Chamaecyparis. Other characters commonly used to circumscribe these taxa (e.g. the configuration of the ovulate cone, the anatomy of the seed, the timing of embryo development) are not constant within each genus, largely due to the conflicting suite of characters observed in Chamaecyparis nootkatensis (D. Don) Spach. As a result of limited taxon sampling and/or the reliance on composite terminals, the monophyly of these genera in the Cupressaceae was not tested by previous phylogenetic efforts. The monophyly of Cupressus and Chamaecyparis is tested with a simultaneous cladistic analysis of organismal data and rbcL sequences. Organismal data, including morphology, anatomy, biochemistry, and embryological development, comprise ca. 50% of the informative characters in the combined matrix. Preliminary analysis suggests that, as currently circumscribed, Cupressus and Chamaecyparis are not monophyletic.

Key words: Chamaecyparis, Cupressaceae, Cupressus, monophyly, phylogeny, rbcL