King of the Meadow

Tuesday, June 20: a disappointing start to the day’s botanizing. The river was finally low enough to allow me to get out to my favorite bedrock terrace, but very little was actually blooming there, except an invasive alien St. John’s wort and, bizarrely, this goldenrod. Um…. it’s still June, y’all!

From there I went in search of basil balm; I found the plants, but nope, not blooming yet.

And then, walking along the towpath, I spotted this. Convenient, considering what I wrote six weeks ago: “On my to-do list for later this year is to find a stand of these and examine them more closely.”

 

 

This is Thalictrum pubescens (Ranunculaceae), commonly known as tall meadow rue or king of the meadow. It’s easily identified in Maryland, as it’s the only Thalictrum here whose stamens stand upright (other bisexual Thalictrums have drooping stamens).

It has a typical Thalictrum compound leaf.

 

 

 

 

Notice how each little subleaflet has three lobes.

 

 

 

Tall meadow rue is polygamo-dioecious: each plant bears either male or female flowers, except for some plants which bear both male and bisexual flowers. This is a male flower [right], consisting only of sepals and stamens (no petals). Typically there are four or five sepals, and many stamens.

Many of these [left] are bisexual flowers, with both stamens and pistils. Typically there will be anywhere from four to fifteen pistils.

 

 

 

Tall meadow rue grows mostly in New England and the Mid-Atlantic, and in some parts of the South and Mid-West. It’s threatened in Indiana. The Maryland Biodiversity Project has records for it in every county except Washington and Somerset. Look for it growing in wet areas, in sun or shade. Along the banks of the C&O Canal, for example.

A Bit More on Thalictrums

This morning, while botanizing with friends in the central Montgomery County serpentine barrens, I tripped across this. It’s another example of Thalictrum coriaceum (maid of the mist). Note how much more brilliantly colored the flowers are. I believe that’s in part because I caught them newly opened, as opposed to senescing.

These plants were also much smaller than the others: about twelve inches rather than thirty six. Why the difference? I’m going to take an educated guess and say habitat. The plants pictured in my last post were found close to the Potomac River, in a woodland that provided dappled sunlight. To judge by the variety and species of other vegetation nearby, I’d guess the soil was mesic (moderately moist) and nutrient-rich. The plants I found today were growing in a clear-cut field, in full sun, on a dry-ish slope on serpentine soil, which is nutrient-poor. (See this post from last September).

I also found this, which I believe to be a stunted specimen of Thalictrum pubescens (tall meadow rue). It, too, was only about twelve inches tall, but otherwise showed the characteristics of that species.

 

I want to stress again that I’m a perpetual student, not an expert. Anyone who disagrees with my assessments, please leave a comment!

The Botanerd’s Handy Guide to Thalictrum Species

After a quick happy hour dinner and art walk on Friday evening, Steve and I settled in at home, each with our laptops, him working on something for his employer, and me trying to understand the genus Thalictrum and identify some plants.

Do we know how to party or what?

I wasn’t getting very far, because my pictures were taken on a windy, overcast day, and high ISO = noise = can’t see details. So I turned to Steve and asked “hey hon, would you be willing to be my assistant on a short hike tomorrow?”

Steve has little interest in botany, but he’s a good sport. Saturday morning, with rain threatening, we hiked quickly to the mystery Thalictrum meadow and took measurements, looked at leaflets with the hand lens, and got some slightly better photos.

I’ll spare you the details of keying out the species, which turned out to be Thalictrum coriaceum, or maid-of-the-mist.

Because I know other wildflower enthusiasts who’ve had difficulty with this genus, I’ve put together a handy guide to identifying the five Thalictrum species found in the Maryland piedmont.

 

If it looks like this, it’s T. thalictroides (rue anemone). I’m not trying to be flip, but rue anemone is the only one of the five species to bear perfect (ie., bisexual) flowers, so it can’t be confused with any of the others.

pistillate flowers of Thalictrum coriaceum

 

 

 

T. coriaceum and T. dioicum have nearly identical flowers. Both species are dioecious, meaning that plants bear either pistillate or staminate flowers. If you see the flowers in late March or early April, and the plants are no taller than two feet, they’re probably T. dioicum.

staminate flowers of Thalictrum coriaceum

 

If you see the flowers in late April or later and the plants are around three feet tall, they’re probably T. coriaceum.

a proximal leaf of T. coriaceum clasping the stem

 

 

 

 

As a further check, examine where the leaves meet the stem. On T. coriaceum, the proximal leaves (the ones closer to the base of the stem) should be clasping, like this.

a sessile distal leaf of T. coriaceum

 

 

 

 

The distal leaves (closer to the tip of the stem) will be sessile, like this. More specifically, according to Weakley’s Flora, the leaf immediately below the lowest flowering branch will be sessile. If you’re wondering how this can be considered sessile, read on.

click on this one!

 

 

The attractive thing about these Thalictrum species, at least to me, is the intricate, airy leaves, which are described as triternate, or triply compound.

 

 

Steve stretches out a leaflet for me to photograph

 

Each leaf has three stems, called petiolules (sub-petioles), that end in leaflets; each leaflet is divided again into three, and each of those divisions is divided once more into sub-leaflets.

An Erigeron shows what a sessile leaf looks like

 

 

 

Sessile generally means that the leaf tissue is directly connected to the main plant stem, without a petiole.

 

 

 

With triternate leaves, the fact that all three petiolules meet at a point directly adjacent to the main stem makes the leaf sessile. Note that in the photo showing a clasping leaf, there’s a little collar of leaf-like tissue surrounding the stem at the place where the petiolules meet it. That collar is lacking from the sessile leaf in the following photo.

The last two species are T. revolutum and T. pubescens. Both usually flower even later than T. coriaceum, and both usually stand taller (up to six feet or more). Examine the undersides of the leaves. T. pubescens will usually be slightly pubescent (finely hairy), though it may be glabrous (smooth). T. revolutum will have small, round bumps or stipitate glands, which look like hairs with teardrops on them. You will probably need a hand lens to see these details. And remember to always examine multiple leaves and see what features the majority of them have.

Crush a leaflet between your fingers and smell it. T revolutum will have a skunky odor. Although the specific epithet revolutum means that the leaves turn downwards at the edges, a useful mnemonic is to remember the word revolting.

I regret that I have no pictures of this plant to show, but I’ve never seen it in the wild. From what I’ve seen on various internet sites, the flowers of this plant look much like those of T. coriaceum, except they’re white.

T. pubescens can be dioecious or polygamo-dioecious (see this post for explanations of these terms). I believe these to be the staminate flowers, but am not sure; I took this picture last summer before delving into Thalictrums. On my to-do list for later this year is to find a stand of these and examine them more closely. And then write about it, of course.

 

When confronted with a large number of details I often make spreadsheets in order to make sense of it all. The information in this chart comes from Flora of the Southern and Mid-Atlantic States, Flora of North America, Illinois Wildflowers, and to a very small extent, my own observations. Any errors are mine.

  T. coriaceum T. dioicum T. pubescens T. revolutum
height to 30″ 25.5″ to 59″ 20″ to 118″ 36″ to 84″
stems glabrous glabrous or glandular coarse glaucous or slightly pubescent
leaves
   proximal      (toward base) petioles clasping petiolate petiolate; petioles often pubescent
   distal (toward the tip) sessile or nearly so petiolate sessile
   basal? no yes yes  no?!
leaf at lowest flowering branch sessile petiole 3-7 cm
leaflets ovate, obovate, suborbicular ovate, obovate, suborbicular ovate, obovate, suborbicular ovate, obovate, suborbicular
3 – 9 lobes 3 – 12 lobes 1 – 5 lobes 1 – 5 lobes
lobe margins crenate lobe margins often crenate lobe margins entire lobe margins entire
leaflet undersides glabrous or glandular glabrous or glandular finely pubescent to glabrous stipitate glands or papillae
flowers pistillate: purplish, standing pistillate: purplish, standing white to purplish pistillate: greenish
staminate: purple with yellow anthers, drooping staminate: yellow, drooping filaments standing staminate: white, drooping
flowering May – July March – April May – July May – August

A final note: Thalictrum is one of those taxonomically challenging genera; different authors recognize different characteristics and different names. This guide is probably not much use outside the Maryland piedmont, where more or different Thalictrum species may be present.

Flower of the Day: Early Meadow Rue

Thalictrum dioicum; Ranunculaceae

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This year I finally got out at the right time to spot this delicate plant in flower.  And then I was confused, because nearby was what appeared to be the same plant, only a little taller, with a distinctly different flower. Looked somewhat like tall meadow rue, but that plant blooms much later in the season.

The guidebooks weren’t much help at first, but then I read in Clemants and Gracie that in this species, male and female flowers are on separate plants.  So off to the internets to fact-check.  Sure enough, the other plant was sporting the female flowers.

above right, closeup of male flowers

below, plant with female flowers
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right, an overhead view of male flowers, showing the sepals; there are no petals

belowone small part of a very complicated leaf, showing leaflets

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Early meadow rue is wind pollinated, and for that reason it’s hard to get a good photo of it: the slightest breeze will set the whole plant moving about.  Using a tripod helped, but the autofocus feature was no good at all – all the plant parts are so insubstantial (and prone to moving) that the camera couldn’t find a way to focus.  I had to go full manual.  And it was shady, so even with a wide open aperture, I had to keep the shutter speed fairly slow.  These  pictures were the best I could do, on two different days.  The next day there’s dead calm, the plant will likely be done blooming.

Anyway, more about the plant: it’s yet another one that likes moist, rich woodlands, growing on rocky slopes and cliffs.  It is one of six Thalictrum species that can be found in Maryland, ranging from Quebec to Georgia and west into the Great Plains.

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