Is Newcomb’s Right About Burdock Petioles?

From Steve Young: Newcomb’s wildflower guide says that Arctium minus, common burdock, has hollow leaf stalks and A. lappa, great burdock has solid leaf stalks.  It would be nice if this was consistent so these species could be identified before they flower since the leaves look alike. I have been cutting off leaf stalks near the base and YES, it seems that they can be distinguished that way. You can’t miss those huge leaves along trails and other disturbed areas.

Common burdock has flower heads up to 1 inch wide on short stalks.

Arctium minus heads

The petioles can have a small hollow center or it can be larger.

Arctium minus petiole

Great burdock has heads larger than 1 inch on long stalks.

Arctium lappa heads

The petioles are solid.

Arctium lappa petiole

However, I have not seen any difference in the deepness of the groove on the petiole.  Both species have deep grooves.  So, check for yourself and see if you find these characters to be consistent.  I would be interested to know what you find.

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