Vegetative anatomy and relationships of Setchellanthus caeruleus (Setchellanthaceae)

On account of its distinctive features, Setchellanthus cannot be included w ithin any of the families of glucosinolate-producing plants. Features unkno wn in any of these families include abundant vasicentric tracheids, abaxial axial parenchyma, and only short uniseriate rays (composed of upright cell s) in wood; and the presence of wide helix tracheary elements in leaves. Wo od offers the greatest number of phyletically significant features, and woo d of Capparaceae offers many similarities, although the wood of Helianthemu m (Cistaceae) is even more like that of Setchellanthus. Despite the fact th at no myrosin cells were observed in Setchellanthus, it appears closest, on the basis of present information, to the glucosinolate-producing families.