Texas Euphorbias, Subgenus Esula

I finally went through all the Texas Euphorbias including a group that has given me some trouble in the past: subgenus Esula. Here are the important characteristics that I came up with that roughly goes from easiest to separate to most difficult or grouped by similar species. There are still a couple that I am having a lot of trouble with, but this should work in general. If not mentioned, assume horned glands, smooth fruits, and entire leaves. For terminology information, please read here.

E. lathyris: Leaves clearly opposite, forming an X shaped pattern going up the stem; plants bluish-green.

E. spathulata: Serrated leaves, no horn-like appendages on the oval glands, and warty fruits

Third photo: E. spathulata: left; E. texana: right. Source observation here

E. texana: Just like E. spathulata but with smooth fruits.

Source observation here

E. helioscopia: Like E. texana but typically with around 5 pleiochasial branches instead of 3 (the main branches of the inflorescence).

E. peplus: Winged fruits.

Source observation here

E. roemeriana: Partially fused dichasial bracts (the bracts that are held in pairs).

E. brachycera: Large perennial plants usually with some triangular-ovate bracts (hard to separate unless you actually see the plants or a picture of the plants).

E. peplidion: Dichasial bracts +/- broadly lanceolate with acute apices.

Source observation here

E. longicruris: Dichasial bracts imbricate notably asymmetric with the ventral half extended, generally distinctly reniform, generally strongly ascending, apices rounded, bases cordate and overlapping if spread; fruits with two raised areas along the keels (not wings) similar to E. peplus.

Source observation here

E. austrotexana: Leaves narrow, linear to oblanceolate or narrowly lanceolate.

E. tetrapora: Dichasial bracts essentially symmetric or slightly asymmetric, generally subdeltoid, generally spreading or weakly ascending, apices typically mucronate, bases generally truncate to subcordate; stems erect, unbranched at the base; fruits with two raised areas along the keels (not wings) similar to E. peplus.

Source observation here

E. helleri: Dichasial bracts mucronate or not, sometimes abruptly narrowing at the middle with a rounded apex; stems ascending, branched at the base; lower leaves often notably emarginate, leaves except dichasial bracts spathulate or oblanceolate.

Source observation here

I'd like to note that E. austrotexana has not been observed on iNaturalist and neither E. lathyris nor E. helioscopia have been observed for Texas if anyone is interested in hunting them down. By the way, I continually update a list of all the species not observed in the US on iNaturalist here.

ID notes on E. peplus, E. longicruris, and E. tetrapora: I have had some difficulty distinguishing these three in the past. They key in very different places making it difficult to ascertain the essence of their differences (especially with E. longicruris as distinctive as the imbricate bracts are and how problematic it can be when considering things like etiolation). Since creating this, the distinctions have been updated and should reflect a more consistent understanding of the species.

Comparison of the fruits of E. peplus (left) and E. longicruris (right):

References:
Original publication for E. austrotexana

Posted by nathantaylor nathantaylor, April 15, 2019 20:31

Comments

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Thank you for your diagnostic efforts on Euphorbia identification and especially for sharing your results with amateurs like me. These plants have certainly been challenging to ID.
But just realized I need to create a concise glossary of the terms used in the descriptions to attach to the info.
No problem.... Part of the learning process, and re-learning process for people like me.

Posted by connlindajo over 1 year ago (Flag)
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A great exercise, @nathantaylor7583 ! Although dichotomous keys are a time-honored tradition in botany, I am finding that making a trait matrix (rows are characters, columns are species) is very helpful to me to identify the unique combinations of traits for each species in a group, and then I highlight those to make a verbal statement "This is the only species in our area that has xxx and yyy." That seems to be pretty similar to the logic you have followed here.

I love the idea of a "species not observed on iNat" list. There's a motivation!

Posted by janetwright over 1 year ago (Flag)
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@janetwright I actually did make an excel document with all the important characteristics. I wish I knew how to upload documents as this is essentially a summary of that. As to the species not observed on iNat list, I was hoping it would be a motivator!

@connlindajo If I knew how to attach photos to journal posts, I'd make a illustrated glossary for the various Euphorbia groups. As it is, I'm limited by the format of the journal posts. I might try to look into it a little today.

Posted by nathantaylor over 1 year ago (Flag)
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To embed, just use a standard html img tag like: [start bracket] img src="https://i.imgur.com/YkMfenY.jpg" width=100% [end bracket]

Posted by kimberlietx over 1 year ago (Flag)
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I guess you have to have the image stored somewhere else online and give a link to that? I'll have to try it, it would certainly make things a bit easier.

Posted by nathantaylor over 1 year ago (Flag)
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Let's see if this works.

Posted by nathantaylor over 1 year ago (Flag)
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There we go. That worked! Thanks for your help @kimberlietx!

Posted by nathantaylor over 1 year ago (Flag)
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I guess it's time to start a glossary.

Posted by nathantaylor over 1 year ago (Flag)
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I did not mean my comment to be criticism in any way... I just have a muddled brain when it deals with things like " Dichasial bracts".
I have joked many times that my next goal in life is to word at least one family taxonomy key in laymen language... using terms understood by folks like me...
Probably a pipe dream.... but when I get caught up, perhaps, I will attempt.
BTW: You have such great photos!!!

Posted by connlindajo over 1 year ago (Flag)
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Don't worry, I didn't take it as a criticism. Creating a glossary is something I've wanted to do on here for some time, but never really looked into it because I didn't think there was a way to add photos.
I hope the parenthetical information helped enough for you to be able to understand. I much prefer the other groups. They are so much easier to write about as well as identify.

Posted by nathantaylor over 1 year ago (Flag)
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:-)

Posted by connlindajo over 1 year ago (Flag)
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Thanks for sharing all of this with us. I appreciate your hard work on the project. I'm bookmarking this in hopes that I can come back to it when I need it.

Posted by suz about 1 month ago (Flag)

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