Wood colors and their coloring matters: a review.

A number of colored specialty woods, such as ebony, rosewood, mahogany and amboyna, and commercially important woods, such as morus, logwood, Brazilwood, Japanese yellowwood, blackwood, kwila, red beech and myrtle beech, exhibit a wide range of colors from black, violet, dark red, reddish brown, to pale yellow. These colors are not only due to colored pigments contained in extractives from those woods but also to insoluble polymers. Wood and bark from many species of both hardwood and softwood trees contain many types of flavonoid compounds. Research on flavonoids has been conducted mainly from two points of view. The first is chemotaxonomy with flavonoid compounds as taxonomic markers, and the second relates to the utilization of woods for pulp and paper and the use of tannins from bark for wood adhesives. Most chemotaxonomic studies have been conducted on flavonoids in the extracts from softwoods such as Podocarpus, Pinus, Pseudotsuga, Larix, Taxus, Libocedrus, Tsuja, Taxodium, Sequoia, Cedrus, Tsuga, Abies and Picea. Hardwood chemotaxonomic studies include those on Prunus and Eucalyptus species. Studies on flavonoids in pulp and paper production were conducted on Eucalyptus woods in Australia and woods from Douglas fir in the USA and larch in Japan. Flavonoids as tannin resources from black wattle tannin and quebracho tannin have been used commercially as wood adhesives. Flavonoids in the bark from radiata pine and southern pine, from western and eastern hemlock, southern red oak and Quercus dentata are also discussed. In addition, the distribution of flavonoids among tree species is described, as is the first isolation of rare procyanidin glycosides in nature.