What Makes an Angiosperm?
If we are to look for the earliest true angiosperms, we must first know what separates the flowering plants from the other seed plants. The obvious answer is flowers! However, other Mesozoic seed plants came perilously close to the “flower habit” without actually crossing the biological line to angiosperm-ness. A variety of characters have been proposed to distinguish angiosperms. Some of those that might be recognized in the fossil record are summarized here: • Simple micro-and megagametophytes. This is one of the most important biological features of angiosperms, but is hard to recognize in the fossil record. Also, if we accept a progenetic mechanism for the transition from gymnosperm-type ovules and pollen to those of angiosperms, the “line” between the angiosperms and everything else becomes quite fuzzy. What constitutes simple? • Ovules completely surrounded by two integuments. This is the feature most often cited as the defining character of flowering plants. Because it is a morp
