A comparison of floral structures of Anisophylleaceae and Cunoniaceae and the problem of their systematic position

Flowers of Anisophyllea (Anisophylleaceae, Cucurbitales) and Ceratopetalum (Cunoniaceae, Oxalidales) are surprisingly similar in appearance. To date, these families have never been interpreted as closely related, and even in present molecular (rbcL) studies they appear in different orders of eurosid s I (APG, Annals of the Missouri Botanical Garden 85:531-553, 1998). In thi s investigation, flowers of selected taxa of both families are morphologica lly and anatomically compared. In addition, previous work on the two famili es is reviewed. The results strongly emphasize the great similarity in all floral organs. Some special similarities include the occurrence of trimerou s flowers, isomerous organ whorls (including the gynoecium), valvate sepals , digitate petals, obdiplostemony, incurved filaments in bud with similar a nthers, similar pollen, similar nectaries, carpels with free styles, a cana l in the centre of each individual carpel as well as in the centre of the e ntire gynoecium along the symplicate zone, and similar ovules with a slit-s haped micropyle. In addition, recently recovered Late Cretaceous floral fos sils that share features of both families further emphasize a potential clo se relationship. However, if more extensive molecular studies are performed in the future that support the current disparate position of the two famil ies, then an explanation of the biological/ functional similarities in flor al structure should be attempted: specifically, whether this suite of Featu res is a symplesiomorphy for basal rosids, or an autapomorphy for each fami ly. (C) 2001 Annals of Botany Company.