Primitive pollen cone structure in Upper Pennsylvanian (Stephanian) Walchian conifers

Abstract

A large number of conifer pollen cones associated with primitive walchian conifers, includingEmporia, occur within an exceptionally preserved fossilized biota near Hamilton, Kansas, USA. The fossils are derived from channel deposits within the Upper Pennsylvanian (Stephanian B/C) Topeka Limestone and show excellent external morphology, internal anatomy, and cuticular features. Pollen cones are cylindrical, up to 5 cm long and 1 cm wide and are simply organized. Each pollen cone consists of a nonwoody central axis from which sporophylls diverge in a helical arrangement. Vascular tissue comprises a ring of tiny cauline bundles that divide at intervals to produce a single trace to each sporophyll. Sporophylls consist of a terete stalk and a heeled distal lamina. Sporangia are attached as a cluster on the adaxial surface of the sporophyll stalk. Stomata occur in one or two bands on the inner surface of sporophyll laminae and consist of guard cells surrounded by a ring of subsidiary cells, each with one overarching papilla. The Hamilton specimens provide conclusive evidence that pollen cones with a distinctive morphology were produced by some of the most ancient walchians from both North America and Europe. Contrary to traditional interpretations, these cones differ significantly from those of the Pinaceae. The broad geographic and stratigraphic distribution of this morphology reveals that conifer pollen cones similar to those at Hamilton are more widespread than previously suspected, and provides evidence for the potentially ancestral morphology of all conifer pollen cones.