A visual encyclopedia of northern U.S. wildflowers

Over the last 40 years, modern techniqu. Many of the "classic" guides were written in a time when the Linnean classification system still reigned supreme, all the way up to "Kingdom Plantae."

Modern phylogenetic techniques have substantially altered the classification of plants above the level of Order. The Angiosperm Phylogeny Group of the Linnean Society of London is responsible for reviewing the most recent research and publishing updates every few years. The relationships at right are a subset of the APG III classification system, from 2009.

The basic taxonomic unit is a "clade", which is defined to be a monophyletic group - in other words, a group whose members all descended from a common ancestor. In the past, taxonomic grouping was made on the basis of physical characteristics, a gross division at first, but carried out with increasing sophistication as time went on. However, modern molecular techniques have allowed a more precise determination of the actual evolutionary relationships between extant species, bypassing the confounding effects of convergent evolution. In many cases, it has confirmed the close relationship of traditional taxa. In other cases, it has confirmed that some taxa are merely "junk drawers" for otherwise unrelatable species. And most importantly, it has sometimes shown that uncontroversial taxa are actually a combination of two or more unrelated groups, and that a reclassification is necessary.

Taken together with the ICBN's normalization of nomenclature, a 2010 view of flowering plant classification differs from the "classic" guides in the following essential points:

  • Goodbye to infraorder, suborders, superorder, infraclasses, and the like. The taxonomic levels above Order are all clades, and there can be any number of clades between an Order and the taxon of all flowering plants (clade angiosperms). All clades are (ideally) defined as being descended from a common ancestor.
  • Eight families have been renamed from their traditional designation, most of them originally defined in the 18th century, in order to provide all families with a consistent suffix.
    • Guttiferae (St. John's Wort family) became Clusiaceae.
    • Leguminosae (Pea family) became Fabacaeae.
    • Cruciferae (Mustard family) became Brassicaceae.
    • Labiatae (Mint family) became Lamiaceae.
    • Compositae (Composites) became Asteraceae.
    • Umbelliferae (Parsley family) became Apiaceae.
    The old names are still recognized, but no longer recommended for use.
  • Several "traditional" families have been coalesced into other families, either at the genus level, or as a subfamily. The most relevant one is Asclepiadaceae, the milkweeds, which has been subsumed into Apocynaceae, the Dogbane family. Sparganiaceae (Bur-Reed) was also merged into Typhaceae (Cattail), and Pyrolaceae (Wintergreen) into Ericaceae (Heath).