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.
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.
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.
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.
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
*information gleaned mostly from Flora of Virginia, Alan S. Weakley; any errors are mine