Iridoid glycosides in the Loasaceae and the taxonomic position of the family

Recently two iridoid glycosides, mentzeloside (I) and decaloside (II), have been isolated from Mentzelia decapetala (Loasaceae) (Bliss et al. 1968, Danielson et al. 1973a, b). By using methods described earlier (Kooiman 1970) the present author isolated loganoside (III) from the seeds of Blumenbachia hieronymi and got evidence by paper chromatography that this compound occurs in leaves and seeds of Cajophora lateritia, Loasa vulcanica, Mentzelia lindleyi and Blumenbachia hieronymi. In the leaves loganoside is accompanied by another iridoid compound which is probably loganic acid (norloganoside). The knowledge that iridoid glycosides occur in the Loasaceae prompted to a consideration of the taxonomic position of the family. Rather generally the Loasaceae are classified in the Violates (Bentham & Hooker 1862-1883; Engler & Diels 1936; Wettstein 1935, although he obviously had his doubts; “Sehr isoliert ist die Stellung der Loasaceae”, and ‘Der Samenbau spricht gegen eine Verwandtschaft mit Caricaceae, Passifloraceae und Cucurbitaceae Melchior 1964, who has the family in a separate sub-order; Cronquist 1968; Pulle 1952). Hutchinson (1967, 1969) assigned the family to the order Loasales, along with the Turneraceae; in his view the order was “perhaps derived from Passiflorales and tracing back to Bixales” (1967). Bixales in the sense of Hutchinson are part of the Violates as used in the present contribution*.