Q: What up with kingdom, order, and class designations for carnivorous plants?

A: All carnivorous plants are (of course) in the "Kingdom" called Plantae.

Our understanding of how plants are related to each other has changed. Until recently, after Kingdom, we commonly divided plants into "Division" (no, not "Phylum"--that is a zoological term), then "Class", then "Order." However, with new insights from genetic work, we are reorganizing these old relationships. And we aren't just reshuffling the ranks--it turns out that it doesn't always make sense to say there are always these three ranks of Divisions, Classes, and Orders.

So what do we have?

We used to say that carnivorous plants were in the "division" called Anthophyta. However, this category was found not to be "monophyletic." (If you are curious what that means, well, you can read about that elsewhere.) But with Anthyophyta turning out to be a bogus classification, a different clade called "Angiosperm" was coined. These are the flowering plants.

With this change in "division," what about the rank we used to call "class?" Here, things are even worse. I think this term is mostly a thing of the past. Instead, we just talk about ranking levels with the generic term "clade."

There are about eight different clades within the Angiosperms, and there isn't clear agreement on how they are related. The arguments among scientists can be fierce--it's like fanboys and fangirls arguing about Star Wars movies. Fortunately, there isn't too much argument about where carnivorous plants fit it. They are all in a group of plants called the "core angiosperms." After that, things are kind of a complicated mess.

I'll show you what I think is a pretty good perspective, which is supported by a consortium of scientists called the Angiosperm Phylogeny Group (APG). Fortunately, many of the controversial points do not affect us much in our conversation, because carnivorous plants are easily classified into just a few of these clades in the angiosperms.

The next four levels of subdivision are "Order," "Family," "Genus," and "Species." Since carnivory in plants evolved several times, they are not all in the same plant Order. On the next FAQ entry I have this information summarized.

By the way, finer-level subdivisions such as subspecies, variety, and form, are used in carnivorous plants. However, the usage is not consistent for all genera. For example, subspecific categories are not widely used in the genus Utricularia, while it is commonly applied in the genus Sarracenia.

Page citations: APG 2016; Greuter, et al. 2000; Raven, et al. 1981; Rice, B.A. 2006a.