Parallel Evolution of Endospory within Hornworts: Nothoceros renzagliensis (Dendrocerotaceae), sp nov.

摘要

The development of a gametophyte within the confines of the spore (i.e. endospory) is one essential innovation toward the evolution of seeds, but this feature also arose in seedless plants. In bryophytes, spores may begin to divide prior to dispersal and germination, but always develop into a free-living gametophyte. In hornworts, multicellular spores occur only in Dendroceros although they have also been observed in cultures of Phaeoceros carolintianus. Here, we describe a new species of Nothoceros, N. renzagliensis, from Pasto, Colombia, that differs from its congeners by its endosporic condition and Dendroceros-like spores. Gametophyte anatomy and sequence data from all cellular compartments place this species within the genus Notheceros and as the sister taxon to all Neotropical Nothoceros. We re-evaluate the evolution of endospory in hornworts and we show two cases of parallel evolution of this trait across the hornwort phylogeny. Endospory seems to be a highly homoplastic feature across all bryophytes with several independent origins in mosses and liverworts.