Tuesday, August 16, 2011

Missouri Ironweed (Vernonia missurica)

As I become a more experienced and knowledgeable botanist it's hard not to play favorites when it comes to certain families and genera of vascular plants.  By now you all know of my passion and deep-rooted love for the wild orchids (Orchidaceae), which more than likely would be placed first on my list of most admired.  There are plenty more that keep those rare and delicate plants company on that list, such as the Ironweeds (Vernonia spp.).  They aren't the showiest nor the rarest species to be found in our wide array of native flora but there's just something about them that really directs my focus to understanding and studying them.

About a week ago I published a post starting my treatment on the Vernonia genus in Ohio and its four members.  It can be found by clicking the link HERE for those interested in getting a grasp on the Tall Ironweed (V. gigantea) and the Prairie Ironweed (V. fasciculata).  I mentioned in that post that I would be attempting to collect, photograph and study the two remaining species that have been recorded from our state.  A difficult task when taking into consideration the rarity of the latter two species; Missouri Ironweed (V. missurica) and New York Ironweed (V. noveboracensis) inside Ohio's borders.  This past Sunday I made the journey to Daviess County in southwestern Indiana with high hopes of finding the third species of Ironweed I'd like to discuss, the Missouri Ironweed (V. missurica).

Missouri Ironweed in native habitat
Flowehead(s) of Missouri Ironweed

My destination was one of the areas most pristine and diverse nature preserves in the state known as Prairie Creek Barrens.  A large expanse of wet prairie containing numerous rare and fascinating plant species has survived years of land abuse from the surrounding agricultural landscape to remain intact and well managed to keep the rare ecosystem thriving.  I plan on doing a separate post about my experiences with the other gorgeous flora of the preserve but my focus was directed at the tall wands of purple swaying in the morning breezes.  At first glance Missouri Ironweed looks almost identical to the much more common Tall Ironweed.  As I mentioned in the previous Ironweed post, habitat differentiation goes out the window with these species as they all prefer wet to moist expanses of open ground with plenty of sunlight and commonly grow together.  In fact, there was Tall Ironweed to be found growing amongst the Missouri in Prairie Creek Barrens.

Taking a look at the corymb of flowerheads it's still not too easy to differentiate from the more common Tall Ironweed.  Both have very similar rayless disk flowers of a magenta color, tightly overlapped phyllaries that look very much alike as is the spacing and density of the flowerheads.  The number of individual disk flowers per flowerhead can be used to separate the two.  Missouri tends to have more, with an average over 30, while Tall Ironweed typically has a number less than 30.  A close glance at the inflorescence's stem or peduncle can begin to clear the air.  On Tall Ironweed the stem is generally finely pubescent if not a bit more smooth and glabrous.  On Missouri Ironweed the stem is noticeable hairy with a dense covering of wooly hairs.  Hair is the name of the game with Missouri Ironweed as you'll come to see when looking at the rest of the plant.

Glancing at the distribution map for this species it's pretty evident this species is most common in the Mississippi river region, with some disjunct populations to the east and west.  Ohio lies at the eastern edge of the range where it's only known to occur in the Oak Openings area (Lucas County) as well as a remnant tall grass prairie patch along the railroad (Clark County).  There have also been recorded collections of a natural hybrid between Missouri and Tall Ironweed in several northwestern counties.  This has lead to some botanists and authors to question the true genetic integrity of Missouri Ironweed in Ohio.  Having never seen Ohio's alleged true V. missurica I really have no opinion in the matter but can understand the skeptical outlook of the doubting minds.

Missouri Ironweed's leaves
heavy pubescence on underside of leaf

The best means to tell the two nearly identical Tall and Missouri Ironweeds apart is to take a look at the stem and the undersides of the leaves, especially at the petiole.  The leaves are arranged alternately and lanceolate in shape with serrated margins like all other Ohio Vernonia's.  Where the differences begin is very noticeable and heavy pubescence of the undersides of the leaves, especially at the petiole.  The numerous small hairs run along the veins and give off a crystalline look to the emerald leaves.  If you remember the picture of the underside of the Tall Ironweed's leaves they lack the obvious pubescence with just a very conservative scattering of hairs, if any at all.

Missouri Ironweed leaves
Missouri Ironweed leaves

The pictures above really drive the nail home at just how hairy the undersides of the Missouri Ironweed's leaves are.  From a ways back the leaves give off a silvery-green sheen from all the hairs.  The stem is another great place to look for the persistence of hairs on the Missouri Ironweed.  Tall Ironweed's stems can range from glabrous to finely pubescent but rarely anything like the display of hairs the Missouri Ironweed puts on.

Missouri Ironweed's stem
Magenta flowerheads of the Ironweed

In my experience the hairs on the stems of Missouri Ironweed are a whitish-clear color while the hairs of the Tall Ironweed are a purplish-brown color.  I've never read or seen where this is a definitive difference and used in the genera's keys, just an observation I've made in my careful examination and breaking down of the species.  I hope to make a trip down into Kentucky to get the fourth and final Ohio Vernonia, the New York Ironweed (V. noveboracensis) that I can add to this treatment and breakdown of the species.  New York Ironweed was only collected once in Ohio over a century ago and has since been marked as extirpated.  It's very distinct phyllaries end in a long, thread-like hair that can quickly separate itself from the rest of the Ironweed's.  Once again I'm sure this wasn't the most fun post for the majority of the faithful readers but it's been fun for me to delve into this genera and really get a hands on understanding of what sets these beautiful and unique plants apart.  Until next time!


  1. Well, it was fun for me, too! This is the kind of detail we don't find in the field guidebooks and can be really useful when confronted with identification puzzles. And you never know when you might come across a plant completely out of its normal distribution range.

  2. Thanks for the informative post. I will have to check the ones in my field...in a post yesterday, I stated a photo was Ironweed, it may need changing a bit! :)

  3. Nice find..one thing we both failed to mention is that hybrids substantally outnumber specimens showing more pure strain characteristics such as your plant here. So finding one like yours is tough.In all probablity as one approaches the core of a species distribution area, the greater the number of purestrain individuals would be likely to be found. We must be on parrallel tracts, as I had finally just found a hybrid which showed 90% V.missurica traits here.Great post.

  4. Woodswalker - Glad you found in interesting! I really enjoy taking a specific genera of plants and getting in depth with them and discovering their every detail. Just one of the infinite fun aspects of botany!

    Wanda - Thanks for the kind words. You're 99% likely to only find Tall Ironweed in Ohio but it never hurts to try :)

    Michael - I would be hesitant to say hybrids ever out-number the pure strain based on the fact hybrids cannot reproduce so their number relies entirely on the chance two plants would happen to cross. In Ohio the other Vernonia species are so rare and scattered finding any hybrids becomes a very rare thing. In areas where more species ranges overlap with each other such as Illinois and Missouri, you are much more likely to find hybrids.

  5. Great post! Without this explanation, I would not have been able to figure out what species of Ironweed grows on our family farm in Robertson County, Tennessee (North Middle TN). I used UT-Knoxville's herbarium website to help narrow distributions. My county has records for two species: Vernonia gigantea and V. missurica. I consulted Jones' Plant Life of Kentucky, but still no help. Checked online for more info, and A.L. Gibson to the rescue! Our plants have rough leaves, but they're not silvery at all, so Giant Ironweed it is! Now I am able to proper label my seeds I collected. Thank you.

  6. Oh, and I agree about admiring the Vernonia species. They have such a lovely attractiveness that just keeps my camera pointed on them, even after they turn to fruit!