The Elm Project, Part 2: American Elm and Slippery Elm

AMERICAN ELM and SLIPPERY ELM are two that I've often had a hard time telling apart. They both have larger leaves than other elm species that grow here, but it isn't really possible to distinguish these two using leaf size. Slippery Elm is named for the slimy "slippery" feel of the inner bark. That's a fine clue, if you can get to the inner bark, but I usually couldn't. Most of the time, the main thing I was using to differentiate them was how rough or smooth the leaf surface was. Slippery Elm is supposed to feel rougher to the touch than American Elm, but this isn't always easy to determine. American Elm leaves are especially variable, with some leaves feeling much rougher than others, even on the same tree. I spent the first months of the summer rubbing hundreds of elm leaves without ever being entirely certain on species. I went back to the books and found that there are actually a number of clues that are simple and clear enough to make sense to me. And these clues do not involve touching the elm leaves at all. (¬‿¬)

AMERICAN ELM (ULMUS AMERICANA) vs. SLIPPERY ELM (U. RUBRA)

1. Here's my favorite: the leaves of Slippery Elm have secondary veins that are frequently forked: most leaves will have more than two forked veins on each side. In American Elm, the veins are rarely forked: most leaves will not have more than one or two per side. This often can be seen clearly in pictures, so is more helpful than texture!
2. Other hints that suggest Slippery Elm rather than American Elm: leaves that taper abruptly to a very long tip, leaves that "fold" upwards along the central vein, buds that are dark rusty-red and downy.
-- Here's an observation by @sadawolk that nicely demonstrates the leaf shape, veins, and buds of a Slippery Elm.
https://www.inaturalist.org/observations/18127315
3. The leaf shape of American Elm is oval in outline, widest at the middle, tapering to a sharp, pointed tip.
-- See this observation by @owenclarkin showing classic examples of American Elm leaves:
https://www.inaturalist.org/observations/14812242
4. Both American Elm and Slippery Elm flower and fruit in the spring, before leaves appear. The fruit of an elm tree is a winged seed called a samara. In American Elm, the samara is elongated (longer than wide) and deeply notched. It is smooth and hairless on the front and back surfaces, but has fine hairs all around the margin. Slippery Elm has samaras that are round (about as long as wide) and are not deeply notched. They are hairless around the margins, but often have fuzz on the front and back surfaces, over the seed in the center. The samaras of American Elm are on long stalks that droop, while the samaras of Slippery Elm are in dense bunches, close to the branches.

• Here’s an observation by @sambiology showing the SAMARAS of an American Elm:
https://www.inaturalist.org/observations/10252244
• Here’s an observation by @sadawolk showing the SAMARAS of a Slippery Elm:
https://www.inaturalist.org/observations/12168095

• Here’s an observation by @sadawolk showing the FLOWERS of an Slippery Elm:
https://www.inaturalist.org/observations/10509089
• Here’s an observation by @ilouque showing the FLOWERS of a American Elm:
https://www.inaturalist.org/observations/19755447

In the third part of The Elm Project, I'll address the two elms with small leaves, Cedar Elm and Winged Elm.

Posted by lisa281 lisa281, January 01, 2019 22:21

Observations

Photos / Sounds

What

American Elm Ulmus americana

Observer

lisa281

Date

February 20, 2019 04:59 PM CST

Photos / Sounds

What

Slippery Elm Ulmus rubra

Observer

lisa281

Date

February 20, 2019 05:02 PM CST

Description

Finally! I’m pretty sure I found a flowering Slippery Elm (that I could reach!) Now if I can just find one that’s fruiting! This tree is very close to the outdoor classroom at the Heard, so it will be easy to get back to it.

Photos / Sounds

Square

What

American Elm Ulmus americana

Observer

lisa281

Date

March 5, 2019 11:12 AM CST

Photos / Sounds

What

Slippery Elm Ulmus rubra

Observer

lisa281

Date

March 12, 2019 06:29 PM CDT

Comments

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Nice idea for a project. I'll just add that Ulmus americana and Ulmus rubra aren't particularly closely-related within the Ulmus genus and in that sense differ in many easy to learn ways. Despite this they are frequently confused in online posts and official articles, typically with Ulmus americana photos being labeled as "Ulmus rubra". Once one is familiar with both species, can contrast their differences to another species couplet: e.g. Ulmus rubra and the European Ulmus glabra which look fairly similar in terms of leaves and fruit

Posted by owenclarkin about 1 year ago (Flag)
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Thanks @owenclarkin for your comment - and for your many wonderful elm observations! I've found several of them very helpful!

Posted by lisa281 about 1 year ago (Flag)
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Glad to hear it!

Posted by owenclarkin about 1 year ago (Flag)

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