ULMUS FROM THE EARLY-MIDDLE EOCENE OF PACIFIC NORTHWESTERN NORTH AMERICA: SYSTEMATICS AND IMPLICATIONS FOR CHARACTER EVOLUTION WITHIN ULMACEAE

Leaves and fruits of Ulmus from the Middle Eocene of British Columbia and Washington are assigned to two species. The first species is based on leaves attached to flowering and fruiting twigs and isolated leaves and fruits. Leaves display a polymorphism ranging from large leaves with compound teeth with blunt apex to small ones with simple teeth resembling Zelkova. In extant Ulmus, sucker shoot leaves, elongation shoot leaves, and leaves on short annual branches display a very similar polymorphism. Flowers are arranged in fascicles having short pedicels. Fascicles are formed in the axils of leaves of current year shoots and appear together with the leaves. This is uncommon in modern species of Ulmus where leaves either appear in spring on shoots of the previous year, or in autumn in axils of leaves of current year shoots. Fruits of Ulmus species 1 are samaras with extremely reduced or absent wings that may have been ciliate along the margin of the endocarp and the persistent styles. The small, shallowly lobed perianth is situated below the endocarp. A second type of foliage is distinct from Ulmus species 1. This foliage is wider and has more densely spaced secondary veins. It also has characteristic compound teeth with primary and subsidiary teeth displaying conspicuously different orientations. Leaves of Ulmus species 2 co-occur with a second type of fruit but have not been found in attachment. These fruits are larger than Ulmus species 1, with a narrow wing, persistent styles, and a large and wide perianth that tapers abruptly into the perianth tube. A tentative cladistic analysis suggests that Ulmus species 1 is nested within the subgenus Ulmus that is a paraphyletic grade basal to the subgenus Oreoptelea. Ulmus species 2 foliage shows affinities to the subgenus Ulmus, while the associated fruits display affinities to the subgenus Oreoptelea.