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.


Monarchs (A Post for Cheryl)


Ta-da!  Here it is, the current darling of conservation, the monarch butterfly (Danaus plexippus).  I promised a friend I’d write about them if I ever actually saw one.  So here you go, Cheryl, this post is for you!

This one was in the Smithsonian butterfly garden on the National Mall, feeding on butterfly milkweed (Asclepias tuberosa).

The monarch is easily mistaken for another butterfly, the viceroy.  The two look a lot alike; the major difference is a dark lateral stripe toward the rear of the viceroy’s hindwings.  I don’t have a picture to illustrate that but have a look at the Maryland Butterflies website.

I’m no entomologist so I’ll stick with a few basic facts.

There are two populations of monarchs, one east of the Rocky Mountains and one to the west.

Most of the eastern population overwinters in Mexico, though some will hibernate on the Gulf and southern Atlantic coasts.  Adults already in the tropics do not migrate.

Monarchs lay eggs on milkweeds (Asclepias species, and two other species in the Apocynaceae).  The caterpillars go through five instars before pupating and emerging as an adult butterfly.  The adults will feed on a variety of plants, including species in the aster, carrot, pea, and mustard families.

Monarchs will produce one to six broods during the summer.  Most of the butterflies live only a few weeks; it’s the last brood of the year that migrates south to overwinter, mate, and return north, laying eggs on the way.

The eastern population has declined by more than 90% since 1995, which is about one billion individuals.

The major threat to monarchs is habitat loss, which takes two forms: destruction of the forests in which the monarchs overwinter, and destruction of milkweeds, the sole larval host plant.  Milkweeds are considered nuisance plants by farmers and many homeowners.  Another threat – and another reason to hate invasive species – is the increasing presence of two species of Cynanchum, exotic alien plants that look like the native Cynanchum laeve (which is a larval host plant) but are poisonous to the larvae.

Other species of butterflies migrate, but the monarch is the only one that migrates both ways.

For more detailed information check out any of the following sites:
USDA Forest Service
Butterflies and Moths of North America
Monarch Watch
The Xerces Society