I think of the elms in our area as coming in three pairs: two introduced species, two species with large leaves, and two species with small leaves. All of them have leaves with toothed margins and asymmetrical bases, and have a “fruit” called a samara, a winged seed. Most have double-serrated margins, that is, each tooth has a break in it, making a second little “tooth.”

In this journal, I’ll address the two introduced species, Chinese (or Lace Bark) Elm, and Siberian Elm. These two differ from the four native species in a couple of ways. First, the leaves are only slightly asymmetrical at the base: often the shape of the leaf looks symmetrical, except that the central vein is off-center. Secondly, the leaves are quite smooth on the top. The leaves are usually toothed, but not double-serrated. The samaras are smooth, both on the surface and around the edges. They never have corky “wings” on the branches or twigs.

LACEBARK/CHINESE ELM (ULMUS PARVIFOLIA) This one is being planted a lot lately, but doesn’t occur here naturally. This tree is most easily recognized by its bark. It has a very distinctive "lacey" bark, flaky and mottled, often with orange-ish underbark showing through. The leaves are smooth on the top surface and are fairly symmetrical at the base, although sometime inequal. The leaves are typically once-serrate. Other than Cedar Elm, it is the only elm occurring here that flowers and seeds in the late summer/fall.
• Here’s an observation by @fratto of a Chinese Elm that shows both the distinctive bark and the leaf shape: https://www.inaturalist.org/observations/18626389

DWARF/SIBERIAN ELM (U. PUMILA) This species is not commonly planted here. There are a few reported here, though, so I’m including it. These are small trees, with leaves similar to Lace Bark Elm: fairly symmetrical at the base, and once-toothed, and smooth on top. They flower and seed in the spring, have seeds that are completely smooth, and do not have the flaky bark of Chinese Elm.
• See this observation by @bob777 of a Siberian Elm
https://www.inaturalist.org/observations/14147874

In Part 2, I'll address the two elms with large leaves, American Elm and Slippery Elm.

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Posted on December 27, 2018 07:21 PM by lisa281