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.