Did ‘Paleo-polyploidy’ Really occur in Proteaceae?

Abstract

Cytological data for 188 species in 65 genera of Proteaceae were collated from the literature. Excluding the occasional infrageneric polyploid, Proteaceae have seven confirmed character states for chromosome number (n = 14, 13, 12, 11, 10, 7, 5). Genera of subfamily Persoonioideae are x = 7, and, on a cytoevolutionary doctrine of ‘paleo-polyploidy’ in angiosperm families, these low chromosome number taxa were hypothesised to represent the ancestral genome of Proteaceae. Chief supporting evidence for this hypothesis is the ancient origin of Persoonioideae in Proteaceae phylogeny. However all current genomes in Proteaceae have features that suggest that they are derived, including those of Persoonioideae with their ‘genomic obesity’, and by reference to the chromosomes of Bellendenoideae (n = 5) and the outgroup Platanaceae (n = 21), quite probably their number is also a derived character state. Furthermore the high chromosome number genera of Proteaceae in subfamilies Proteoideae and Grevilleoideae (n = 14, 13, 12, 11, 10) have genomic lengths that are far smaller than would be expected from a doubling of the chromosomes of Persoonioideae, and, so far as any information is available, these genera are also genetic diploids. This paper questions ‘paleo-polyploidy’ as a general cytogenetic mechanism for plant macroevolution at the levels of genus, tribe and sub-family in Proteaceae. It is proposed that diploid cytoevolutionary processes of chromosome number increase and decrease from a primitive genome of FN = 24, with specific examples of x = 12 and x = 21, can explain the cytological phenomena in the family.