Asters - Common Blue Wood vs. Large-Leaved

Hi Folks! Anyone have any good tips on identifying between asters, particularly those with blue/violet flowers and specifically between the Common Blue Wood [Symphyotrichum cordifolium] and Large-leaved Aster (Eurybia macrophylla)?

The guidebook I use for the area I’m in only lists the large-leaved aster, but it is not the most comprehensive book, and I have recently seen some IDs for the Common Blue Wood aster that I am sure I would have identified as Large-leaved if it were up to me…


I’m assuming you’re somewhere on the American east coast. An easy and quick resources are the keys offered by GoBotany:


One of my favorite bits about the iNaturalist community is people know where to find ID keys and share those links. Thanks, @mertensia for the aster keys - they are tricky little plants to ID but so common on the American East Coast.

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I focus a lot on characteristics of the phyllaries for plants in Asteraceae (little green bracts below the flower–inflorescence technically). Also, for those two plants in particular Eurybia macrophylla has a petiole that gets really wide and kind of clasps the stem while S. cordifolium does not. Its petiole is relatively thin. Great pictures of important plant parts for ID can be found at

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Which must be mighty difficult, seeing as this is an all-too-familiar conversation:

Would-be identifier: “Do you have any pictures of the back?”
Observer: “No, sorry.”

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