J Syst Evol

• Research Articles •    

Evaluating the status of fern and lycophyte nothotaxa in the context of the Pteridophyte Phylogeny Group classification (PPG I)

Hong-Mei Liu1, Eric Schuettpelz2, and Harald Schneider3*   

  1. 1Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun 666303, Yunnan, China
    2Department of Botany, National Museum of Natural History, Smithsonian Institution, Washington, DC 20013, USA
    3Center for Integrative Conservation, Xishuangbanna Tropical Botanical Garden, Chinese Acade-my of Sciences, Menglun 666303, Yunnan, China
  • Received:2020-03-16 Accepted:2020-05-19 Online:2020-05-21

Abstract:

Hybridization has long been recognized as common in ferns, but the products of this arguably evolutionary important process have often been ignored in classifications. For example, the recently published Pteridophyte Phylogeny Group classification (PPG I) covered all hierarchical ranks from class to genus but did not include intergeneric hybrids (nothogenera). Here, we provide for the first time a comprehensive evaluation of previously proposed nothogenera in the context of a current phylogeny‐based pteridophyte classification (i.e., PPG I). We find that several nothogenera nested in the orders Osmundales and Polypodiales are supported in the framework of PPG I, but others are superfluous. Five new nothogenera are introduced here for the first time. We also explore the distribution of nothospecies across the pteridophyte phylogeny for the first time. We are unable to reject the hypothesis that species richness and nothospecies diversity are correlated, despite the finding that some temperate lineages contribute more nothospecies than expected whereas several tropical lineages lack them. This pattern could be the consequence of either fundamental differences in modes of speciation in temperate and tropical zones or unequal efforts to record nothospecies. In general, we emphasize the need to take nothogenera into account when proposing generic classifications, but the information provided by the existence of such hybrids needs to be carefully evaluated. Our results underscore the need to report and study hybrids in ferns and lycophytes, especially in biodiversity rich areas.

Key words: hybridization, nothogenus, nothospecies, species richness