Families with highest proportions of rare species are not consistent between floras

Aim In this study we compare the incidence of rarity within lineages betwee n three floras: Australia, North America and New Zealand. Methods We used published data for absolute numbers of species and for numb ers of rare species to ask three questions: 1. Do families have similar pro portions of rare species in different floras? 2. Can proportions of rare sp ecies within families be interpreted with reference to biogeographic histor y of particular floras? and 3. Is the proportion of rare species consistent between families and genera within each flora? Results Within families in each flora, genera usually had similar proportio ns of rare species; indicating processes determining rarity are in general not operating differentially within families. However, in comparisons withi n-family between floras, approximately 62% of comparisons showed significan t differences in the proportion of rare species. Main conclusions These results imply that there are no general rules whereb y the particular traits a family possesses are conducive to rarity wherever they occur. Rather, such attributes must exert influence conditionally, in conjunction with the biogeographical and competitive setting where speciat ion and extinction or persistence has occurred.