Cretaceous origin of dogwoods: an anatomically preserved (Cornaceae) fruit from the Campanian of Vancouver Island.

BACKGROUND

Cornaceae consists of 58 species, all within the genus . The Cenozoic record of is extensive and well documented. Molecular divergence-time studies suggest that crown-group may have originated by the Late Cretaceous. However, there has been no formal report of from Cretaceous deposits. Here, we characterize a permineralized fossil fruit assignable to subg. from the Upper Cretaceous (Campanian) Shelter Point locality of Vancouver Island, British Columbia, Canada.

METHODS

Serial sections of the specimen were made using the cellulose acetate peel technique. Peels were mounted onto microscope slides and studied by light microscopy.

RESULTS

The fossil fruit consists of a tri-locular woody endocarp with dorsal germination valves. The locules are sub-triangular to ellipsoidal in transverse section and are separated by thin septa. Endocarp tissue consists of elongated and isodiametric sclereids and secretory cavities. Internal vascular tissue was not observed, but is interpreted to have been located along the outer periphery of the septa for some length, common in many cornalean taxa. There is one seed in each locule, one of which was found to have endosperm and a dicotyledonous embryo.

DISCUSSION

Woody endocarps with germination valves, without central vascular bundles, and with one seed per locule are characteristic of several families within the order Cornales. The interpreted vascular pattern and presence of secretory cavities indicates that the fossil fruit is assignable to subg. . Comparative analysis suggests that the fossil is most similar to , a species described from the Paleocene of North Dakota. This fossil is the first evidence of crown-group Cornaceae from the Cretaceous and sheds light on both the plesiomorphic fruit characters and the timing of the initial diversification of the family and basal asterid lineage, Cornales.