A new treatment of Pilosella for the Euro-Mediterranean flora

Abstract

Recognising Pilosella as a genus distinct from Hieracium is justified both from a phylogenetic point of view (a more broadly defined Hieracium, to be monophyletic, would have to include at least two fur- ther genera along with Pilosella: Andryala and Hispidella) and for practical considerations. In Hieracium, almost all taxa are apomicts that rarely hybridise, and whenever they do, give rise to new, stable apomictic lines that are customarily given taxonomic recognition as species or subspecies. In Pilosella hybridisation is frequent, gene flow between populations (however defined) is considerable, and the recognition of microtaxa as if they were apomictic lines is unpractical. The classification here proposed rests on a framework of twenty accepted “basic” species (some with subspecies) or species aggregates. Hybrid progenies in which 2-3(-4) of these species or aggregates are believed to have par- ticipated are treated as 122 “collective species”, one per known or postulated parental combination. Each of these comprises one recognised species, or sometimes more than one when an included morphotype is stable over a significant, coherent area, or when the offspring of a particular subspecies or microspecies combination deserves recognition. A synopsis of the proposed classification is pre- sented, and required new names and combinations are validated.