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So the difference between E purpureum and E maculatum is ...

I'm doing more plant pics, and got to some new pics of Eupatorium maculatum. Hmm, that's right, somebody told me a year or so ago that most of the Eupatorium purpureums they've seen were actually Eupatorium maculatum. What was the difference again? Ah yes, and yes.

Eupatorium maculatum, spotted Joe Pye weed, has stems that are spotted dark purple or (sometimes) purple all the way.
Eupatorium purpureum, sweet Joe Pye weed, gravel root, has stems that are purple only at the leaf nodes.

Lemme check my online pics ... right, that's the purpureums into the maculatums then. Oh well. And here I've used the root of the maculatum as if it was a purpureum. Hmmm. And Harding says the two are picked together and can be used interchangeably. Hmmm.

It's good to know that real live botanists make that same mistake: the plants in the old botanical garden in Helsinki have purple stems and are labelled "Eupatorium purpureum". Tsk tsk tsk. (The plants in the new bot.g. are purple-stemmed and labelled "Eupatorium maculatum". Good show!)
This reminds me of the old saying that 25 % of labels in botanical gardens are wrong.


Now to find some real honest Eupatorium purpureum seed, with stems that are dusty instead of purple or spotted, and with the funky leaf nodes ... or perhaps I'll just go on using the maculatum as if it was a purpureum. You can't usually do that with Eupatoriums, but these two are close enough, seeing that the maculatum used to be a variety of the purpureum, long ago.


I recollect Matt Wood told-me-that 7song told-him-that (already the makings for a tall tale) he (7song) didn't know for sure that they should be considered separate species at all... that 7song had even gone out to the sites where the maculatum was collected as specimens and found purpureum. I think that's written in the Book of Herbal Wisdom as well...

In one of my wildflower books both species are listed, but it appears to be the same plant; one picture being taken when the flowers were just coming on, and the other when they were in their peak Eupatorial-fuzziness.

I can't apply this to gravel root/joe pye, but I know a spot where there's a stand of Water Hemlock in which some stems are spotted and purple, some only where the leaf stems come out, and others are straight green from root to leaf. As the "spotting" and color of the stems is often listed as a means of identifying Water Hemlock, this is notable.

But I don't think these are different species of Cicuta... is stem color in Eupatoriums really a valid means of differentiating the species?

There was something about the stems being hairy (maculatum) as well, but I couldn't find it this time around. I expect we should locate a Eupatorium botanist; they'd know for sure.

As to Cicuta spottiness, AFAIK it has to do with the amount of sun the stems get.

Well I saw my name and came across this page, and I don't know if this will help any, but I figured I'd at least quote myself directly.
First, I have not yet seen, even after many years of looking, a Eupatorium purpureum plant in the wild. I found seeds and am growing one in my garden, so I at least finally know they exist.
While they look a lot alike, there are a few noticable differences.
Eupatorium maculatum is a wetland plant, while E. purpureum prefers drier upland environments. And on a more botanically significant detail, E. maculatum generally has more than 10 flowers (range 8-20) per infloresence (involucre) while E. purpureum generally has 4-7. While this seems very involved, it is easy to count the flowers per head by gently grasping the involucre and twisting it thereby releasing the individual flowers (florets), and then counting.
The purple-ishness of the stems is less useful as this can change plant to plant.
One of the other distinctions is something I have not found yet, that the E. purpureum is supposed to have a distinctive vanilla-like odor. This is the reason I initially began this identity quest, as I figured that to have this odor might involve coumurins or some other class of active chemicals that would give E. purpureum different or more potent properties . Alas, I will keep on looking. I hear that E. purpureum is more common in Missouri, so I will look for (and smell for) it when I'm in that neck of the woods.

Thanks for that, 7Song!

My Eupatorium doesn't have spots/speckles nor is it purple at the leaf nodes or elsewhere. What other criteria can I use to determine whether it is purpureum or maculatum?

(BTW, what an obnoxious anti-spam screener--making me lie about herb my preference!)

If 7Song's definition up there ^ doesn't do anything for you, you might wish to try botanical sites for exact specifications on the Eupatoriums.