A sinkhole pond high on a ridgetop? Just one of the strange qualities of Overcup Oak Natural area, a pure stand of Quercus lyrata (Overcup Oak) in Shannon County. In certain parts of Missouri a karst topography exists. This land surface is created as rainwater filters down through limestone or dolomite to form large caverns and caves. When too much rock dissolves, the cave's ceiling collapses and a sinkhole appears. Overcup Oak Sink, once much deeper, is now a shallow sinkhole depression with little runoff from rainfall and a heavy subsoil. These factors created a wet to moderately moist soil condition in the midst of an upland dry-mesic forest where this unusual stand of overcup oak trees grows. These oaks are usually found in the bottomland forests of the Missouri Lowlands Natural Division. The acorn of this species is unique because the globular nut is almost completely enclosed by a rough cap, leaving only the tip exposed. (May 18, 2009)