Studies on Fossil Azolla: Azolla Montana, a Cretaceous Megaspore With Many Small Floats

Azolla montana is a new species from the late Cretaceous; it has a megaspore apparatus with a single large and conspicuous columella which resembles the floats of the megaspore apparatus of many extant species. The columella differs from true floats in being pilose, like the perispore of the megaspore body. The 10–20 small true floats are appressed to the columella, and are difficult to distinguish from it. It is suggested that the floats were derived, phyletically, by segmentation of the columella; the columella represents the primitive “float” of the megaspore apparatus.