Honey Locust and Macano: Legumes, not Varieties

A friend of mine recently wrote about the “living fence” tree that is called macano (Diphysa americana) here in Panama. He mentioned in passing how the leaves reminded him of the honey locust. And so they should. The honey locust leaves (from the scroll saw village website) are on the left and a far less glamorous photo of macano leaves from A Neotropical Savanna is on the right:

I commented to my friend that indeed the two trees were related – they’re both in the same family. And promptly someone observed that, to paraphrase, the macano must be a variety of the honey locust.

Well, I didn’t rant back on the careful use of language, but I thought it would be fun to see if I could get the point across here.

If you’re talking about plants, then a variety is a plant that varies from other plants in the same species (or subspecies) in minor, but inheritable ways. To get a sense of just how minor the differences are, I’ll use a neat chart from wikipedia to show the major groupings in biology. The groups go from least-closely related (at the top) to most-closely related (at the bottom).

Each group contains a collection of the groups below it. So Life is now considered to consist of three Domains (two domains of single-celled organisms without a nucleus and one domain of organisms with cells that contain a nucleus). The domain of nucleated cells contains the Plant Kingdom, the Animal Kingdom, and more. And so forth.

Note that the word “variety” is not on this chart. That’s because a variety is a grouping within the smallest group on the chart.

We’ll just jump right down to the Family grouping.

I said earlier that the honey locust and the macano were in the same family. That family is the legume, or Fabaceae, family.

Now, each of the groupings in this chart can have subgroupings, and it happens that the Fabaceae family has three subfamilies. One of those three is the pea subgroup (Faboideae, with nearly 13,000 species), and both the honey locust and the macano are in this subfamily. Notice how the flowers of each resemble the pea flower; honey locust on the left (permission from minnesotamom), macano on the right, click either to enlarge.

So they’re not only in the same family, they are also in the same subfamily. But that’s as far as it goes. They are not in the same genus.

• The genus of the honey locust tree is Gleditsia and the genus of the macano is Diphysa.

If they are not in the same genus, they cannot possibly be in the same species.

• The species of the honey locust is G. triacanthos and the genus of the macano is D. americana.

To give each their full scientific name, with the genus name first and capitalized and the species name second and not capitalized: honey locust = Gleditsia triacanthos and macano = Diphysa americana.

Consequently, neither can be a variety of the other because the honey locust and the macano differ in major and important ways, so major that they must fall not only into different species but into different genera.

Okay, end of rant. Wasn’t that fun?

Fabaceae