Selaginellaceae Milde

Abstract

A nearly worldwide family based on the heterosporous genus Selaginella. The spores are trilete, tetrahedral-globose, or nearly spheroidal, and often have an equatorial flange. The microspores are mostly echinate and may be retained in tetrads. The exospore is plain, verrucate, or spinulose with different types of fine structure, and is covered by either a special paraexospore of sporopollenin or a perispore. Some species may lack the outer wall. The megaspore surface is often reticulate or with coarse contours and additional granulate, papillate, or echinate material. The exospore is of two distinct zones—an inner compact region, and a much larger, outer labyrinth or gridlike formation that is often heavily infiltrated with silica. The endospore is formed before completion of sporogenesis in both types of spores. Spores from strata as early as the Devonian have been associated with the family, but later records from the Pennsylvanian can be assigned to the Selaginellales with confidence.