Astery Things #8: White Disk Flowers

 a common buckeye (Junonia coenia) on late boneset –>

Now that we’re into October one of the white-flowering aster family plants I wanted to write about (late-flowering thoroughwort or late boneset) is just about done blooming, but the other one (white snakeroot) is going strong still.

Both of these plants were once placed in the genus Eupatorium, but in 1970 the snakeroots were moved to the genus Ageratina*. Interestingly, it took a long time for the guidebooks to catch up. Newcomb’s Wildflower Guide (1977) and Field Guide to Wildflowers (National Audubon Society; 1979) still refer to white snakeroot as Eupatorium rugosum. The earliest printed reference to white snakeroot as Ageratina altissima that I can find (in my small library) is from 1993, in The History and Folklore of North American Wildflowers (Timothy Coffey).

[above left: E. serotinum being inundated by Japanese stiltgrass and something in the Polygonaceae; above right: A. altissima]

But enough about taxonomic history; more about the plants: from a distance they look similar: tall, leafy forbs with large arrays of fuzzy, white, joe-pye-like flowers. But close up, the differences become clear and it’s trivial to tell which species is which.

Despite the name “late-flowering thoroughwort”, Eupatorium serotinum blooms in August and September, while Ageratina altissima blooms from September into October (this year, anyway). E. serotinum stands about a meter or two tall; A. altissima stands at about a meter at most. Both tend to be single-stemmed with occasional branching, more so up top.

The flowers of each are borne in corymb- or panicle-like arrays, E. serotinum tending to be a bit flatter overall, and A. altissima being somewhat rounder. Both species produce only disk flowers, the long styles protruding to give a feathery effect (like in joe-pye weeds). Most of the time the flowers of E. serotinum seem more tightly bunched together and more tightly closed, while A. altissima flowers are more open, the five petals easy to see. Also note that the phyllaries of E. serotinum are covered in fine white hairs (A. ageratina phyllaries sometimes have a few sparse hairs).

Here’s where it’s easy to tell the difference. Both plants have opposite leaves (mostly). The leaves have petioles, but the leaf shapes are distinctly different. E. serotinum has lance-shaped leaves that often curl in a bit at the edges. A. altissima has more-or-less ovate to heart-shaped leaves. Keep in mind that, as with so many aster-family plants, the leaves tend to get smaller and more linear further up the stem, and near the inflorescence they can be alternate rather than opposite.

Both of these species can be found in the eastern half of North America; E. serotinum‘s range is more southerly (it barely gets into New England), and A. altissima’s range is more northerly (it barely gets into Florida).

Late-flowering thoroughwort is one of about a dozen or so Eupatorium species whose native range includes the Maryland Piedmont. For three years now I’ve been wanting to write about all of these, but I don’t have pictures that clearly illustrate the differences. Also, the taxonomy is a bit confusing. I need to make a study of it when I can find good examples of the plants, key them out, and take better pictures.

There’s only one other species of Ageratina in Maryland, A. aromatica, aka lesser snakeroot. Here’s a picture from 2014; I haven’t seen one since.






* “A Revision of Ageratina (Compositae: Eupatorieae) from Eastern North America” Andrew F. Clewell and Jean W. Wooten, Brittonia, 1971

Astery Things #4: Blue Mistflower

Next in the series of posts on composite flowers lacking ray florets is blue mistflower. Like the joe-pye weeds, blue mistflower was once placed in the genus Eupatorium, but nowadays it’s known as Conoclinium coelestinum. The flowers are somewhat similar in appearance to joe-pyes, the heads of tightly clustered disk florets with long protruding styles giving the inflorescences a fine, feathery, misty look.

click on this one to zoom in and see the minute flowers opening on the outside of the heads

Also like joe-pye weeds, blue mistflower likes wet soils; along the banks of the Potomac River, if I see joe-pyes, I’m almost certain to find blue mistflower nearby. Unlike joe-pyes, the plants are short, getting to about two feet tall in ideal conditions.

Speaking of the Potomac, I went back out to check on the spot I reported on last week, a place where in other years I would definitely find mistflower. It was all underwater again. Lots of rain upstream.

Blue mistflower ranges mostly along the Mississippi River basin and its tributaries, from southern Illinois south, and also in the eastern mid-Atlantic and the Carolinas. It’s found in most of Maryland except for the westernmost and easternmost parts of the state.

eastern tailed-blue butterfly (Cupido comyntas) sipping from mistflower

Apparently these flowers are a great nectar source for a variety of butterflies, but I haven’t seen many on it. Three years ago I wrote that I was worried that the blue mistflowers in my garden would become weedy*. “Weedy” is, of course, in the eye of the gardener. They certainly have spread, somewhat aggressively, and I’ve had to pull some out, but they haven’t reached weed status yet.


*Lepidopterans Photobomb My Mistflower Shoot

Astery Things #2: The Joe-Pye Weeds

Eutrochium fistulosum

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.

Eutrochium maculatum

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
shapes deltate-ovate narrowly lanceolate lance-elliptic lance-ovate
  ovate broadly lanceolate lanceolate ovate
  lance-ovate lance-ovate deltate-ovate
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
number (4-)5-9(-10) (4-)5-7 (8-)9-20(-22) (4-)5-7(-8)
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.

E. fistulosum: hollow stem

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.

E. fistulosum: a whorl of 4 broadly lanceolate leaves

E. fistulosum: a loose corymb of flower heads















E. maculatum: whorl of three leaves, purple-spotted stems


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).

E. maculatum: lanceolate-ovate leaf










Eutrochium species with purple node

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.

And then there’s the icing on the cake: joe-pye weeds attract bees and butterflies like crazy.

More about this next time.




Eupatorium perfoliatum

I’m not sure what compelled me to look closely at this particular cluster of tiny white fuzzy flowers.  They’re all over the place at this time of year, in the form of late-flowering thoroughwort and white snakeroot.  But for some reason I pulled the kayak up close to this one islet near Fletcher’s Cove, and there it was.


This was a big deal because I’ve never actually seen this plant, despite it being fairly common.  What sets it apart from the other Eupatoriums is the paired, clasping, opposite leaves that make it look like the stem is piercing a single leaf.

There’s nothing about the flowers to distinguish them from other bonesets or thoroughworts.

Boneset likes sun or a bit of shade and wet soils and is tolerant of flooding, so the rock outcrops near the banks of the Potomac are perfect habitat for it.  The native range is from Texas north into Manitoba and all the way east to the Atlantic.

The genus Eupatorium once contained hundreds or species, including (in this area) the various bonesets/thoroughworts, mistflowers, snakeroots, and joe-pye weeds.  Those last three have been moved to other genera, but that is a subject for another day.


…hey, what about the other white flowers in that picture?  Stay tuned!

Another Visitor to Joe-Pye

An hour or less after shooting the skipper and swallowtail (see previous post), I saw a third species of butterfly on another joe-pye weed.



This one is spicebush swallowtail (Papilio troilus). Note the eastern tiger swallowtail in the background.





dorsal view





ventral view




extreme closeup

And now, a confession: I was so focused on shooting the butterflies, I forget to take a close look at the plants.  The plants shown here and in the previous post are likely sweet joe-pye weed, Eupatorium purpureum (Asteraceae), but I don’t have a single picture showing the critical details for a definitive ID.

I think I just gave myself an assignment for later this week.