Once upon a time there was a genus of plants called Eupatorium. It was a large genus, lumping together plants commonly known as thoroughworts, bonesets, mistflowers, snakeroots, and joe-pye weeds. Roughly twenty years ago, the genus was split into twelve or more genera. Thoroughworts and bonesets are still Eupatoriums; mistflowers are now Conoclinium, and snakeroots Ageratina. Joe-pye weeds, those plants with large arrays of pink-purple flowers and whorled leaves, were placed in the new genus Eutrochium.
Historically, four of North America’s five Eutrochium species were found in Maryland, but one of them, E. maculatum (spotted joe-pye weed), has been extirpated. The other three are
- E. dubium (eastern or coastal plain joe-pye weed)
- E. fistulosum (hollow joe-pye weed, trumpetweed)
- E. purpureum (sweet, sweet-scented, or purple node joe-pye weed)
Distinguishing these four species from one another is fairly straightforward, provided you can look at mature, flowering specimens. Here is a much abbreviated chart of some identifying characteristics, taken from the Flora of North America, with the most useful ones in bold purple:
|E. dubium||E. fistulosum||E. maculatum||E. purpureum|
|purple-spotted||purple||purple spotted||dark purple at nodes|
|sometimes solid purple||sometimes spotted||sometimes solid purple||greenish to purple-green|
|solid||hollow||solid; may be hollow at base||solid; may be hollow at base|
|arrangement||in whorls of 3-4||in whorls of 4-6(-7)||in whorls of (3-)4-5(-6)||in whorls of 3-4(-5)|
|venation||3-nerved||pinnately veined||pinnately veined||pinnately veined|
|margins||coarsely serrate||finely serrate||sharply or doubly serrate||coarsely serrate|
|bases||abruptly contracted||gradually tapered||gradually tapered||gradually tapered|
|or abruptly tapered||or abruptly tapered|
|found only in coastal plain||over 6 feet tall||wide distribution||known to hybridize|
|and inland along major rivers||morphologically variable||morphologically variable|
When trying to identify plants in the field, remember to look at the totality of characteristics rather than focusing on one or two, because there can be so much variation from plant to plant. And also because you really shouldn’t be cutting into plant stems in the field, at least not in areas where plants are protected.
Here are a few pictures to illustrate. Keep in mind that these are garden plants; wild-growing specimens rarely look so lush and full. Also, the E. maculatum pictured in this post is not the species, but rather a cultivar (‘Gateway’). Still, it’s not too far off what a wild plant looks like.
And here are a few of E. maculatum. It’s worth noting that further up on the stems, the leaves were in whorls of four (but I couldn’t get a good picture up there).
This picture from four years ago is probably of E. purpureum, though I was never able to get close enough for a confident ID. At any rate, it shows what a purple node looks like.
Of course none of this is what makes joe-pye so interesting. It’s those flowers. Unlike the aster I wrote about in the last post, joe-pyes have no ray florets – only disc florets. Each floret consists of five pointed petals, fused at the base, from which a single long style emerges. The cumulative effect of all those tiny flowers, from 4-24 per head, dozens of heads in each corymbiform inflorescence, up to a dozen inflorescences on each stem, often multiple stems from one plant… it’s just breathtaking.
More about this next time.