Kaplanopteridaceae fam. nov., Additional Diversity in the Initial Radiation of Filicalean Ferns

The Pennsylvanian filicalean fern Kaplanopteris clavata gen. et comb. nov. is reconstructed on the basis of permineralized vegetative and fertile frond segments and rhizomes. Characteristic anatomy conforming to morphospecies Anachoropteris clavata Graham allows for integration of new observations and reevaluation of material from Ohio with published data into the whole-plant reconstruction. Epiphyllous rhizomes arise laterally along frond rachides and feature terete exarch protosteles. Fronds are planar, tripinnate-pinnatifid, with alternate division. Vascular traces of all frond members have adaxial, exarch protoxylem. Rachides and primary pinnae have adaxially convex C-shaped traces; secondary pinna traces are terete. Pinnules are laminar, with lobed margins and open dichotomous venation. Tripinnate latent croziers equivalent in complexity to whole fronds arise on otherwise mature frond segments at the position of primary pinnae. Superficial abaxial indusiate sori exhibit gradate maturation and include numerous leptosporangia producing trilete spores. Sporangial capsules are bent away from the center of the sorus at the juncture with the long, uniseriate stalks. The annulus is a band of two to three rows of interfingering cells, wrapped around the long axis of the sporangium and covering most of it. The longitudinal stomium faces toward the apex of the sorus. Kaplanopteris clavata is reconstructed as a primarily vining plant with organography overwhelmingly dominated by the frond and a unique life-history pattern influenced by growth from two types of foliar-borne reiterative units: latent croziers and rhizomes. Kaplanopteris combines characters known exclusively in fossil filicaleans with both plesiomorphic and derived characters of living filicaleans. This novel combination reveals the existence of a previously unrecognized lineage of basal filicaleans and justifies placement in a new family. Kaplanopteris illustrates the diversity and complexity reached during the first major evolutionary radiation of filicaleans.