Wood and Bark Anatomy of Ranunculaceae (Including Hydrastis) and Glaucidiaceae

Wood anatomy of 14 species of Clematis and one species each of Delphinium, Helleborus, Thalictrum, and Xanthorhiza (Ranunculaceae) is compared to that of Glaucidium palma tum (Glaucidiaceae) and Hydrastis canadensis (Ranunculaceae, or Hydrastidaceae of some authors). Clematis wood has features typical of wood of vines and lianas: wide (earlywood) vessels, abundant axial parenchyma (earlywood, some species), high vessel density, low proportion of fibrous tissue in wood, wide rays composed of thin-walled cells, and abrupt origin of multiseriate rays. Superimposed on these features are expressions indicative of xeromorphy in the species of cold or dry areas: numerous narrow latewood vessels, presence of vasicentric tracheids, shorter vessel elements, and strongly marked growth rings. Wood of Xanthorhiza is like that of a (small) shrub. Wood of Delphinium, Helleborus, and Thalictrum is characteristic of herbs that become woodier: limited amounts of secondary xylem, parenchymatization of wood, partial conversion of ray areas to libriform fibers (partial raylessness). Wood of Ranunculaceae other than Clematis has numerous narrow vessels, probably an adaptation to cold more than drought. Glaucidium has occasional scalariform perforation plates like those almost universally present in Paeonia, but the two genera differ strongly in other wood features. Wood of Hydrastis (scalariform perforation plates occasional in primary xylem, rare in secondary xylem) accords with the idea that Hydrastis is a lineage that separated from the base of Ranunculaceae. Features that ally Ranunculaceae with other families of Ranunculiflorae include presence of wide multiseriate rays (without accompanying uniseriate rays), vessel restriction patterns, and storied structure. Woodiness in Ranunculaceae is probably secondary, at least to some extent; the woodiness of Xanthorhiza, thought by some to represent a primitive genus in the family, could be either primary or secondary.