If you did not see part 1 of this post, please take a look at its first paragraph. This post is more on the fall 2009 publication by the Angiosperm Phylogeny Group, the report called APG III. What I’m giving here is how APG III differs from my book, A Tour of the Flowering Plants. This post is primarily for Montessori botany studies and general learners that own my book. (And if you are interested in acquiring A Tour of the Flowering Plants, see www.bigpicturescience.biz.)
The changes in the eudicots include the assignment of Geraniales and Myrtales to the malvids (eurosids II) branch of rosids. These two orders were previously found to be within the rosids, but their exact location was not clear. Now they are sister lineages that branch near the base of the malvids.
Caryophyllales is listed before the asterids, while the Saxifragales is listed before the rosids. This is the way I depicted these lineages on the informal tree diagram in my book, A Tour of the Flowering Plants. The former Caryophyllales family, Portulacaceae, has been divided, as it held several not-closely-related genera. The genera Claytonia, Montia, and Lewisia have been moved to the new family, Montiaceae.
Lastly the Dipsacales order (in the campanulids or euasterids II branch of the asterids) has had several former families combined into an expanded Caprifoliaceae. The twin flower family – Linnaeaceae, the valerian family – Valerianaceae, the teasel family – Dipsacaceae, and the bush honeysuckle family – Diervillaceae have all become part of Caprifoliaceae. This leaves Dipsacales with only two families, Adoxaceae and Caprifoliaceae.
There have been a number of adjustments in smaller families that are not common in temperate North America. I view these as tweaking the twigs, not establishing the branches. All-in-all, the bulk of the APG scheme has been reaffirmed in the last several years.
What difference do all these changes make? Unless you are an editor of scientific papers, it isn’t absolutely necessary to learn the minor adjustments to the APG scheme. The main thing that students need is the phylogenetic view of life and of the angiosperms. If they see these plants as descendents of a common ancestor and know the major lineages, that’s good. Some may want to delve deeper and that should be encouraged. Mabberley’s Plant Book: A portable dictionary of plants, their classification, and uses (third edition, 2008) by D. J. Mabberley is a valuable reference for further study and to help sort out the changes.
How does the Angiosperm Phylogeny Group classification affect horticulture and native plant identification? I can more easily answer when it will affect these two – that will be over a period of time. Field manuals aren’t going to be re-written overnight and horticultural labels frequently lag behind academic classification. Nonetheless, I think that phylogenetic classification will eventually take over. It certainly makes more sense to focus on the APG scheme and look to the future if you want to address plant classification.