MATTHEWS, MERRAN L.1*, PETER K. ENDRESS1, JÜRG SCHÖNENBERGER1,2, and ELSE MARIE FRIIS2. 1Institute of Systematic Botany, University of Zurich, Zollikerstrasse 107, CH-8008 Zurich, Switzerland; 2Department of Palaeobotany, Swedish Museum of Natural History, Box 50007, S-104 05 Stockholm, Sweden. - Anisophylleaceae and Cunoniaceae: Why are their flowers so similar?
Flowers of Anisophylleaceae and Cunoniaceae are remarkably similar.
Their current phylogenetic position based on molecular studies places
them in eurosids I, but in different orders, Cucurbitales and
Oxalidales, respectively (APG, 1998). We studied flowers from selected
genera of both families and compared them at a morphological,
anatomical and histological level, with some surprising results. This
study, combined with a review of previous work on these families, has
revealed many shared features including the occurrence of trimerous
flowers (in addition to tetra- and pentamerous flowers), digitate
petals, isomery in all floral whorls, obdiplostemony, incurved
filaments in bud and similar anthers, similar pollen, similar
nectaries, carpels with free styles, and similar ovules with a
slit-like micropyle. A timely coincidence was the recovery of well
preserved fossil flowers from the Late Cretaceous of Sweden by JS and
EMF that share many features with both Anisophylleaceae and
Cunoniaceae (but have been placed in Cunoniaceae based on some
specific traits of the gynoecium). Combined, these results suggest
either that Anisophylleaceae and Cunoniaceae are more closely related
than previously assumed, or if not, that they exhibit either an
unusual number of symplesiomorphic features of basal rosids, or that
their floral features are the result of a striking convergent
evolution. In either case, it is apparent that more extensive
molecular studies are needed, and if these studies confirm the current
disparate position of the families, an investigation of the
significance of the suite of common structural features should be
made.
Key words: Anisophylleaceae, Cucurbitales, Cunoniaceae, eudicots, floral structure, Oxalidales