EXTINCT JUGLANDACEOUS WOOD FROM THE EOCENE OF OREGON AND ITS IMPLICATIONS FOR XYLEM EVOLUTION IN THE JUGLANDACEAE

Clarnoxylon blanchardii gen. et sp. nov. is a new taxon for fossil woo d with a suite of features diagnostic of the Juglandaceae. It occurs a t two Middle Eocene (c. 43-44 million years b.p.) localities in the Cl arno Formation of central Oregon, USA. Clarnoxylon resembles the Platy caryeae and the Hicorieae in having exclusively simple perforation pla tes and solid pith. However, the common occurrence of crystalliferous idioblasts in the rays, but not in the axial parenchyma, and the co-oc currence at Clarno of platycaryoid fruits and pollen unaccompanied by hicorioid fruits indicate that Clarnoxylon has affinities with the Pla tycaryeae. Differences between Clarnoxylon and Platycarya support prev ious suggestions that short vessel elements, helical thickenings, and vascular tracheids are derived characters of Platycarya. These differe nces are also in accord with the ecological adaptation of the extant g enus Platycarya to a temperate climate contrasting with the tropical M iddle Eocene setting of Clarnoxylon.