How to ID Sumacs (Rhus) - Dichotomous Key & Video

Hi, all!

In my ~1.5 years on iNaturalist, I've learned a great deal about the genus Rhus and how to identify the Sumacs of North America. For some reason, these species have piqued my interest since I was a kid and noticed red spiky fruit on the side of the highway.

I decided to try and make a comprehensive video guide and dichotomous key for Sumac identification in the United States. I am pasting my dichotomous key below, as well as the identification video. I would love some feedback on the key since it is my first time creating one, and on the video as well! Also, if you find an error in the video or key, please let me know!

I hope this helps you learn to ID new plants! @lisa281 has put together a very nice list of guides for plant identification that I find to be extremely useful. Check that out as well! Thanks, all!

Dichotomous Key
Dichotomous Key using leaf appearance US Sumac Identification:
1a. Simple, alternate leaves. Found on West Coast or Arizona (go to 2)
1b. Compound leaves (go to 3)

2a. Leaf folded along the mid-rib. Taco-shaped leaves or similar. Entire margins. Occurs on West Coast or Arizona = Sugar Bush (Rhus ovata)
2b. Leaf shape mostly flat, not folded. Sharp, holly-like teeth along leaf margins. Occurs only on West Coast = Lemonade Berry (Rhus integrifolia)
2c. Consistent taco-shaped or curved leaves with many teeth along leaf margins. Occurs in sympatric zones on West Coast = Lemonade Berry x Sugar Bush Hybrid - (Rhus integrifolia x ovata)

3a. Trifoliate compound leaves. Middle leaflet generally the largest. = Fragrant sumac / Skunkbush (Rhus aromatica / Rhus trilobata)
3b. More than 3 leaflets in the leaf (go to 4)

4a. 5-9 leaflets (go to 5)
4b. Mature leaves have greater than 9 leaflets (go to 6)

5a. Leaflets very small in size - 6-9 mm long, 2-5 mm wide. Leaves are winged. = Little Leaf Sumac (Rhus microphylla)
5b. Leaves are dark green, shiny in appearance. Leaves are not winged. Leaflets larger in size (1 inch). = Evergreen Sumac (Rhus virens)

6a. Leaflets are entire / smooth along margins (go to 7)
6b. Leaflets are serrated (go to 8)

7a. Leaflets are usually shiny, have large wings on rachis and are wide. Leaflets number anywhere from 9 to 21. Found in Eastern US from Texas through Missouri and up the east coast to Massachusetts. = Shining Sumac / Winged Sumac (Rhus copallinum)
7b. Leaflets lanceolate, curved and much more narrow. Found in the prairies of Texas with small populations in west Texas and New Mexico. = Prairie Flameleaf Sumac (Rhus lanceolata)

8a. Branches, fruit, stem and inflorescence ALL exhibit dense pubescence (go to 9)
8b. Branches, fruit, stem and inflorescence are smooth, exhibit no pubescence at all. Leaf petiole is typically pink. 9-31 leaflets. = Smooth Sumac (Rhus glabra)
8c. Pubescence not found on all features simultaneously. Hairs are sporadic, short and vary. See above links for more details = Northern Sumac (Rhus x Borealis, Rhus typhina x glabra).

9a. Leaflets number 9-31 and are generally longer and narrow. Commonly found in the Northern US and Canada, but can reach some southern states. = Staghorn Sumac (Rhus typhina)
9b. Only found in small regions of North Carolina, Virginia, Georgia, and South Carolina with reports of populations down to Florida. Rare species. Leaflets number anywhere from 7-13. Teeth protrude further out. Leaflets are more rounded, shorter and not as narrow. = Michaux's Sumac (Rhus michauxii)

Posted by conboy conboy, June 14, 2020 17:19

Comments

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Very nice! (You're so ambitious tackling the sumacs of North America - I’m just trying to master the ones we have around here. ) I think Sumacs are really cool, too! I think they have the MOST interesting leaf scar I’ve come across! I can’t speak to the non-Texas sumacs, but as far as the ones I’m familiar with, the key looks great. ( One thing - I think you must have accidentally erased the species ID for 7b (at least that’s what usually seems to happen to me) I guess it should be R. lanceolata ?

I’ll add this to my list of helpful guides. Thanks for your work on this!

Posted by lisa281 about 1 year ago (Flag)
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Thanks a lot for your feedback and for adding it to the guide @lisa281! I fixed that for 7b. The leaf scars are definitely unique on some of these species :)

Posted by conboy about 1 year ago (Flag)
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Excellent work, @conboy! I see you chose not to get into the question of distinguishing R.& nbsp;trilobata from R. aromatica. Even though I side with the folks who says they are two species and once was well practiced at making the distinction, I have despaired of keeping up with that question. I'll leave it as someone else's battle.

Posted by baldeagle about 1 year ago (Flag)
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Thanks a lot, @baldeagle! I agree that’s it’s probably two species, but I chose to stay away from that for now. Maybe one day it’ll be sorted out more clearly! 😆

Posted by conboy about 1 year ago (Flag)
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Not any time soon, I suspect. :-)

Posted by baldeagle about 1 year ago (Flag)

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