The anatomy of IOS Group la (part of Leptocereeae and part of Echinocereeae) was examined to determine if these genera have characters that are relictual in Cactoideae. Echinocereus lacks fibrous wood and seemed distinct from genera with fibrous wood, which constitute the majority of Group la. Excluding Echinocereus and other genera with non-fibrous wood, Group la has many features presumed to be relictual: epidermal cells with ordinary shapes and thin walls, a tendency to have patches of multiseriate epidermis, hypodermis of a few layers with walls of medium thickness, cortical bundles with caps of primary phloem fibers but lacking clusters of terminal tracheids, presence of medullary bundles (and these have xylary fibers), fiber caps next to primary phloem of the stele, presence of fibrous wood and lack of any derived wood types. Derived characters that do occur are not universally present or even widespread in the group. Little evolutionary modification has occurred in Group la, except for Echinocereus.