Rosaceae Phylogeny home

Cladistic analyses of molecular (ndhF, rbcL: Morgan et al. 1994, nrITS: Campbell et al. 1995) and non-molecular data place four genera (Kageneckia, Lindleya, Porteranthus, and Vauquelinia) at the base of an enlarged Maloideae clade. These four genera were previously ascribed to the polyphyletic assemblage "Spiraeoideae".

Results from ndhF, non-molecular, and rbcL analyses place other members of the "Spiraeoideae" (e.g. Physocarpus) as sister taxa to the enlarged Maloideae clade.

Floral development, particularly early gynoecium and ovule development, in Vauquelinia and Physocarpus (Evans and Dickinson 1999) is quite similar to that observed in the Maloideae (Evans and Dickinson unpublished data).

All Maloideae genera, plus Kageneckia and Lindleya, have a base chromosome number of x=17. Vauquelinia has x=15, and Porteranthus x=9.

The inclusion of Porteranthus at the base of the Maloideae clade provides additional evidence for the origin of the subfamily by a polyploidization event (x=18?) within the "Spiraeoideae," followed by reduction in the number of chromosomes (x=15, 17).

If the Maloideae originated within the "Spiraoideae" then the fleshy "pome" fruit (e.g. apple) was derived from the expansion of the hypanthium (floral cup). Incorporation of the ovaries by the enlarged hypanthium resulted in the inferior ovaries present in the majority of Maloideae genera.

ndhF and rbcL are chloroplast-encoded genes that represent the maternal genome only.

Non-molecular data (e.g. morphology) may be encoded by both maternal and paternal genomes.

Thus the alternative hypothesis (ancient hybridization between amygdaloid and spiraeoid ancestors) cannot be rejected on the basis of available evidence.

Investigate the nuclear encoded gene Granule Bound Starch Synthase (GBSSI: "waxy") within a large number of Rosaceae and outgroup genera:

1) nuclear genes are a product of the recombination from both parental geneomes

2) the large size of the gene (~ 4.6kb in potato) may produce a larger number of phylogenetically informative characters than is available in existing Rosaceae molecular data sets (ndhF, nrITS, rbcL).

3) data sets that are more phylogenetically informative are required to infer well-supported relationships within the Maloideae, as well as deeper relationships within the Rosaceae

Preliminary results (Evans et al. in prep) demonstrate multiple copies of the "waxy" gene in the Rosaceae

Determining the extent of copy number within each subfamily may provide additional molecular evidence for evolution within the Rosaceae, particularly with respect to the origin of the Maloideae

Investigation of a number of putative outgroups may help determine the group(s) that are most closely related to the Rosaceae

All photographs on these pages copyright © Rodger Evans 1999.

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