The anatomy of the secondary xylem of the Rubiaceae confirms the relationship between genera and tribes as delimited and arranged by recent authors (Bremekamp, Verdcourt). Two character complexes can be distinguished, the distribution of which is in accordance with the classification of the genera and tribes and to a certain degree of subfamilies as well. Exceptions to this rule occur, but mostly in genera of an uncertain taxonomic position. Henriquezia is an example. Cinchona, by some taxonomists considered to be congeneric with Ladenbergia, differs in its wood anatomy from that genus and from the other Cinchoneae. Rubia fruticosa and other woody members of the chiefly herbaceous tribe Rubieae deviate so strongly in their xylem structure from the other Rubiaceae that an excentric position in the family is suggested.