Publication Details (including relevant citation information):
Buzgo M, Lucas CM, Miller AP, Witherington S (2010) Psilotaceae and Ophioglossaceae: odd twins, until you look twice. Stogran J. et al. [eds], Botany 2010 - Providence, Rhode Island July 31 - August 4. Abstract 242.
Surprisingly in the eusporangiate ferns, molecular phylogeny places Psilotaceae next to the Ophioglossaceae, while the two differ greatly in morphology. Ophioglossaceae have a complex leaf that carries an extravagant sporophore, while Psilotaceae are considered to lack leaves, to bear very rudimentary sporangia directly on their aerial stems, and to lack roots. We show that the aerial structures of Psilotum are not at odds with molecular data, andPsilotum recalls the sporophores of Ophioglossaceae. We suggest that the aerial frond inPsilotum actually represents a leaf, or a stem organ identity that is irreversibly different from the subterranean stem. The multiplicity of sporophores reflects a homeotic evolutionary step involving modifications of the shoot apex meristem maintenance.
Molecular phylogeny has increased our understanding of evolutionary relations, but also risen questions regarding the evolution of the non molecular features that are actually the target of selection, namely morphology and anatomy. Evolutionary Development (EvoDevo) addresses these questions, linking molecular evolution with the morphological and anatomical developmental pathways of organisms.
Namely in old lineages, great gaps have opened between molecular and morphological analysis, probably because of the long evolutionary history and extinctions. Among the ferns (Monilophytes), eusporangiate ferns represent ancestral stem group, but have lost many taxa. The two sister families Ophioglossaceae and Psilotaceae are particularly enigmatic. This study can shed light onto one of its biggest mysteries: the origin of leaves in ferns and seed plants.