Leave This Soapberry? Or Uproot This Chinese Pistache? How Can I Tell?

In the woods of Central Texas, you will find saplings of both the native western soapberry (Sapindus drummondii) and the highly invasive Chinese pistache (Pistacia chinensis). We want to preserve and nurture the soapberry, and to do so we must control competition from exotic invaders. But there is a special challenge here: because both species produce even-pinnate compound leaves, sometimes produce wings along the rachis (especially when young), and often produce odd-pinnate compound leaves (again, especially when young), telling them apart takes more than a cursory inspection.

Most guides rely on the scent of the leaves:

  • The leaves of S. drummondii have a nondescript aroma—the kind of smell produced by the crushed leaves of just about any plant not noted for its scent.
  • For most people, the scent of P. chinensis is a repulsively overwhelming mix of pine, citrus, camphor, and kerosene. (As with wine or fine chocolate, different people pick up different notes.) Personally, I put it somewhere on the scale between demonic and downright horrid, but a few people actually find it attractive.

So usually telling whether a sapling is one or the other is as simple as rubbing a leaf and sniffing. But what about that second sapling? Are you smelling its scent, or the residual pistache from the first sapling's leaves? And what if reaching the sapling means going through poison ivy? Or greenbrier? Wouldn't it be nice to be able to tell the two apart visually?

Fortunately, you can. And often the answer is quick: If the leaves or immature stems show any hint of redness—even a shade just barely to the orange side of lemon yellow—it is not a soapberry. If you have otherwise narrowed it down to these two species, it's Chinese pistache.

Failing that, telling the two apart is still easy, if you look closely. You will find differences in these traits:

  • Bark. On the western soapberry, the bark of just-hardened stems is usually light gray—in fact, almost white. On Chinese pistache, it's usually cinnamon colored. (If you have narrowed the identification down to these two species and any segment of the tree has cinnamon-colored bark, it's Chinese pistache.)
  • Tips of the twigs. On western soapberry, bud breaks near the end of the twigs are usually very short. The direction of growth varies slightly from one bud break to the next, so the tips of the twigs are almost always slightly crooked. On Chinese pistache, the bud breaks tend to be much longer, so usually the end of a twig, stem, or trunk will be ramrod straight.
  • Branch angles. The branches of western soapberry emerge at moderately wide angles—say, 15 to 50 degrees or so, but branches of Chinese pistache emerge at angles much closer to 90 degrees. Often when you're examining the growing tip of a sapling you will see near the tip a lateral branch that has emerged at no more than a 30-degree angle, cinching the identification.
  • Branching pattern. In addition to the wide branching angle, Chinese pistache tends to branch out in an idiosyncratic pattern—a pattern you will never see on a soapberry. It won't appear everywhere on the tree, but you can usually detect it somewhere. Starting from the lowest node (branching point), follow the central stem of the sapling. Usually there will be a relatively wide span with no lateral branches at all, and then bam! Several branches come out at about the same wide angle, and the next segment of the central stem continues for another relatively long uninterrupted span before several branches appear at once again. The groups of branches are nearly whorls, but they don't all emerge from the same node. They are all close to the bud break, but not all at it. Examining the whorl-ish groups more closely, you will see that the more branches each includes the more unequal the branches are in strength. Often one is much, much stronger than all the rest; occasionally two or three are all the same strength; often most are very weak. This general pattern will repeat itself along the trunk and all significant branches. Sometimes it does so only sporadically, but you usually can find it at least once on saplings no more than knee high and two or three times on saplings that have reached head high. As the trunk or main branch increases in size, the number of laterals branching out in each of these whorl-ish groups will increase. The disparity in the strength of the laterals increases, too.

I'm sure there are many more structural details we could use to differentiate these two species, but these macroscopic cues have worked very well for me.

Oh, there is one more, very important test: If the tree passes all of the above tests for Chinese pistache, check out its root system. Be sure to separate every bit of dirt from every one of its roots. Look at it, and then toss it into an appropriate place—a compost pile, a shredder, or up in the branches of another tree or bush. Come back and reexamine it in a week. If it dies, it was Chinese pistache. If it lives, repeat the test, just to be sure.

Unless, of course, you are observing the trees in China.

Julkaistu 25. marraskuuta 2021 20:36 käyttäjältä baldeagle baldeagle


Thank you @baldeagle , have no doubt I will be referring to this often. :)

Lähettänyt franpfer yli 1 vuosi sitten (Lippu)

Great guide. Thanks!

Lähettänyt cynodon 8 kuukautta sitten (Lippu)

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