Tetracentron Fruits from the Miocene of Western North America

An infructescence from the Middle Miocene of Clarkia, Idaho, conforms to the extant Asian trochodendraceous genus Tetracentron. The infructescence of Tetracentron remberi sp. n. bears numerous sessile fruits in a helical arrangement. The fruits are thin-walled capsules with two pairs of greatly recurved hornlike styles that protrude basally from the lateral margins of the fruit. The adaxial surface of the style is papillose and is covered with tricolpate pollen that also corresponds morphologically to that of extant Tetracentron. The new fossil shows that Tetracentron, like the related Trochodendron, was formerly established in western North America, whereas both of these genera are now endemic to eastern Asia. Although these two genera were sympatric in the Miocene of Clarkia, Idaho, they have nonoverlapping geographic ranges today.