This section is from the book "Harper's Guide To Wild Flowers", by Caroline A. Creevey. Also available from Amazon: Harper's Guide To Wild Flowers.
P. erectum is stouter, erect, 2 feet or less tall, with broader leaves. There is a yellowish tint to the flowers and stem by which it may be known. Flowers, 1 or 2 in the leaf axils. Leaves jointed to the sheaths, which are the distinguishing mark of the buckwheat family.
This and the preceding are quite common weeds.
 
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