APG II submerges both Aceraceae and Hippocastanaceae as synonyms of Sapindaceae. Stevens (APG
website) cites an abstract (Li, et al., 2006a) in support of synonymizing Aceraceae within
Sapindaceae. This abstract appears to be based on the same data later published by Li et al.
(2006b).
Li et al. (2006b) used two chloroplast non-coding regions, psbM-trnD and trnD-trnT. In
their analyses, Xanthoceras, traditionally placed in Sapindaceae, was a sister taxon to
a clade that included a monophyletic Aceraceae and monophyletic Hippocastanaceae. Thus,
according to this preliminary analysis, if Xanthoceras is included in Sapindaceae, Sapindaceae
is rendered paraphyletic if either Aceraceae or Hippocastanaceae are recognized. However, this
is not the end of the story.
Gadek et al. (1996) used chloroplast rbcL in an analysis that included taxa relevant to
Sapindaceae. Based on very limited sampling, they found a monophyletic Aceraceae and a
monophyletic Hippocastanaceae. They did not sample Xanthoceras, thus leaving open the
question of the paraphyly of Sapindaceae.
Harrington et al. (2005), based on rbcL and matK, found that Xanthoceras was placed
within the traditional Sapindaceae. However, the anomalous Chinese endemic
Handeliodendron, placed in Sapindaceae by Rehder, was found to be nested within the
Hipoocastanaceae clade as a sister taxon to Aesculus. Handeliodendron has deciduous,
opposite, palmately compound leaves, as in Aesculus. Based on this, we (the YYPG) continued to
recognize Aceraceae and Hippocastanaceae as separate from Sapindaceae, but placed
Handeliodendron (which see) in Hippocastanaceae (YYPG, 2006).
Recently in the Flora of China, Handeliodendron was placed in Hippocastanaceae
(Nianhe Xia, Nicholas J. Turland & Paul A. Gadek, 2007).
The premature lumping of Aceraceae and Hippocastanaceae into Sapindaceae by APG II is
regrettable, an example of basing classification on preliminary unstable phylogenies with poor
sampling of taxa. Lumping these taxa accomplishes nothing other than creating confusion when
dealing with the MASSIVE taxonomic and ecological literature over the last century in
which these families are recognized. |
