Woods of the Vitaceae—fossil and modern

Abstract

Vitaceoxylon tiffneyi gen. et sp. nov. and Vitaceoxylon carlquistii sp. nov. from the Middle Eocene Clarno formation are the oldest known woods with characteristics of the Vitaceae. They are characterized by a tendency to two diameter classes of vessels, wide and tall rays, and a high proportion of their area is vessel. Other characteristics include septate imperforate elements, scanty paratracheal to vasicentric parenchyma, idioblasts in the rays, crowded alternate intervessel pitting, and vessel-parenchyma pits with reduced borders. Wood anatomy of the major extant genera of Vitaceae was examined and compared to the fossils. Features of secondary xylem useful for distinguishing between genera in the Vitaceae include vessel size and arrangement (two distinct diameter classes or not, radial multiples or tendency to tangential multiples), vessel pitting (scalariform or alternate), crystal type (prismatic, druses, and/or raphides) and location (in chambered parenchyma and/or ray parenchyma), cambial variants (present or absent). Wood anatomy supports the proposed close relationship of Cissus to Cayratia. Pronounced vessel dimorphism occurs in temperate Vitaceae; cambial variant structure occurs in tropical Vitaceae. Despite their conformity with Vitaceae at the family level, the two fossil woods are not comparable to any one extant genus. This contrasts with the Vitaceae seeds from Clarno, all of which are referable to extant genera. Two new combinations for fossil woods of the Vitaceae are proposed: Vitaceoxylon ampelopsoides (Schönfeld) comb. nov., and Vitaceoxylon megyazoense (Greguss) comb. nov.