The Pottiaceae s.str. as an evolutionary lazarus taxon

Genomic studies have shown that evolution can be based on clusters of genes that may be silenced and reactivated by regulator genes or promoter sequences. Thus, apparent phylogenetic homoplasy may actually represent a single complex developmental response to selection, involving many genes or gene clusters and one or more regulating sequences, and as such may be called multiplex homoiology. Evidence for such complex exaptions (pre-adaptions) in many organisms is discussed, and two features of the Pottiaceae (Bryopsida), the complex gametophytic morphology characterized by the pleisiomorphic Timmiella, and the twisted peristome complex of 32 filamentous, spiculose teeth, distal to a basal membrane are suggested to be likewise homoiologous. The latter complex trait may have reappeared in the family 4 to 7 times. Inasmuch as exaptions may skip branching events tracked by nested sets of non-coding traits, and because genetic isolation alone is not a good basis for classification, this paper re- evaluates past evolutionary schema in light of this theoretically acceptable exception to Dollo's Law that complex traits are never re-evolved.