As a follow-up to the last post, here are a few more pictures of Robin’s plantain.
Inflorescence with two flower heads
inflorescence seen from behind
pubescent leaves of the basal rosette; conspicuously hairy stem
a small colony
Robin’s plantain, Erigeron pulchellus
Over the years I’ve seen many fleabanes in many different locations. Mostly they were Erigeron annuus (annual fleabane) or E. philadelphicus (common fleabane). Sometimes they were E. strigosus (daisy fleabane).
Always I looked closely to see if maybe I’d found E. pulchellus (Robin’s plantain). Sometimes I thought I had; I’d pore over the pictures I’d taken and read yet again the descriptions in various books, and always I came to the conclusion: nope, not this time, not Robin’s plantain.
Then one spring day in 2022 I was walking in the Gold Mine Tract near Great Falls when a stand of aster-y looking flowers caught my eye. “What are those?” I wondered. “They look like fleabanes, but… oh wow, that’s Robin’s plantain!”
When it comes to identifying Robin’s plantain, my best advice is, you’ll know it when you see it: it looks like the more common Erigeron species, but is different enough to make you think twice. Here’s a grossly oversimplified rundown of how to differentiate the four fleabane species found in Maryland*.
Start by looking at the stem leaves. If most of them are sessile (maybe slightly petiolate), then the plant is either E. annuus or E. strigosus.
many toothed sessile leaves
If the stem is crowded with leaves, and most of them are distinctly toothed, then it’s E. annuus. Look for basal leaves; if there aren’t any, that’s another indicator for E. annuus.
fewer leaves on stem; leaves mostly entire
If there are only a few stem leaves, and they’re mostly entire, then it’s E. strigosus.
If most of the stem leaves are clasping, then the plant is either E. philadelphicus or E. pulchellus.
clasping leaf, margin entire
If the stem leaves are only slightly toothed at the bottom of the plant, and entire further up the flowering stem, then it’s probably E. philadelphicus.
wavy leaf margin, clasping; also note the conspicuously hairy stem
If they’re wavy or more obviously toothed, then it’s likely E. pulchellus.
There are other, maybe better ways differentiate these two species. Look at the inflorescence. If it’s obviously branched and bearing many flower heads, then it’s E. philadelphicus.
If it’s unbranched and bearing only a few flower heads, then it’s E. pulchellus. (Also, E. pulchellus heads tend to be larger with many fewer ray flowers than E. philadelphicus.)
Also consider the habitat. E. philadelphicus is found in moist soils in disturbed areas (fields, roadsides) and is much more common. E. pulchellus is a plant of dry woodlands and prefers rocky areas, like the bluffs in the Gold Mine Tract.
above left, common fleabane; above right, Robin’s plantain
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*information gleaned mostly from Flora of Virginia, Alan S. Weakley; any errors are mine
My friend P wrote that when I posted a picture of purple-headed sneezeweed (Helenium flexuosum) on social media. I included a few pictures in my August 7 post here, but want to share a few more. It’s such a photogenic flower! That’s a pearl crescent (Phyciodes tharos) sitting on the flower head.
Here are a few more pictures from my August ramblings on the banks of the Potomac.
fogfruit, aka frogfruit (Phyla lanceolata; Verbenaceae)
blue vervain (Verbena hastata; Verbenaceae)
riverbank goldenrod (Solidago racemosa; Asteraceae)
tall meadow rue (staminate flowers; Thalictrum pubescens; Ranunculaceae)
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
Last week when I drove to Lock 6 in search of the two Verbesina species, I was pleasantly surprised to find two Helianthus species growing in the same area. Sunflower species can be tricky to differentiate, but I’m fairly confident that these are H. decapetalus and H. tuberosus. Here’s a closer look at both.
First thing to note is that these were likely planted here, and are growing in rather rough conditions (lots of foot traffic, dogs, invasive alien plants, lawn mowers), so neither stand is showing the plants at their best. Depending on what source you consult, both thin-leaved sunflower (H. decapetalus) and Jerusalem artichoke (H. tuberosus) stand anywhere from half a meter to two meters tall. Many sources seem to agree that generally, the former is not as tall as the latter.
The leaves of each species look very similar. The largest leaves of H. tuberosus are usually somewhat larger than the largest leaves of H. decapetalus, but keep in mind that there is a lot of morphological variation in Helianthus species. Note that in this picture, the H. decapetalus leaf has more pronounced teeth, which is another general characteristic. Serrated margins like this are best observed on lower stem leaves. Also, note that both leaves are winged to some extent. Both leaf margins and presence of petioles are characteristics that can vary widely, even on the same plant.
Here’s another look at the leaves. Can you see that there’s a textural difference? Although not entirely smooth, H. decapetalus leaves are much smoother than H. tuberosus leaves, which feel like sandpaper. (In the above left photo, H. tuberosus is on top and H. decapetalus is on bottom. In the above right photo, H. tuberosus is on the right and H. decapetalus is on the left.)
Another, more obvious difference is seen in the stems. H. decapetalus stems are mostly smooth, maybe with a few short hairs. H. tuberosus stems are covered in short hairs that stick straight out.
About the flowers… Clearly they look a bit different. Don’t let the specific epithet decapetalus fool you, because this species does not always have ten ray florets (“petals”). It will usually have about ten rays, though. H. tuberosus has about ten to twenty, though some sources say as few as six and as many as twenty-five. In these two populations, the ray florets look a little different, a little wider and rounder on H. decapetalus, and a little longer and narrower on H. tuberosus.
As with the verbesinas in my last post, I caution you against using any one characteristic, or any one flower head or leaf, or any one section of stem, to determine the identification. You really need to look at the entire plant – several leaves, several flower heads, several stem sections – to be sure.
Helianthus identification is fraught with peril. It’s highly likely that I have H. tuberosus here, but there is one other Helianthus in this area that has hairy stems: H. hirsutus. These two look similar at the stem, but the latter species has much longer and narrower leaves, which are either sessile or with very short petioles. H. hirsutus is listed S1/highly state rare in Maryland. I’ve never found it, so I can’t share any pictures to illustrate the point.
Another tricky ID involves H. strumosus (pale-leaved sunflower), which is hard to distinguish from H. decapetalus. The major difference is seen in the phyllaries (aka involucral bracts) on the underside of the flower head. In H. strumosus, they don’t usually spread out past the width of the disk of the flower head, while in H. decapetalus, they do spread beyond the disk. I’ve never seen H. strumosus. The picture above shows the involucral bracts of H. decapetalus.
Here’s one more Helianthus, just for fun: H. divaricatus (woodland sunflower). The differences should be obvious.
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