Leaf Pair and Stipule
Moosomin Regional Park
Note the pair of opposite leaves. There are also two stipules, but the second is obscured behind the first in this photograph.
Note that the key to the family in Budd's Flora requires "leaves with stipules, appearing whorled". The leaves of this species do have stipules. However the stipules do NOT resemble the leaves, and therefore the leaves do NOT appear whorled. See genus Galium in this family for stipules which do resemble the leaves, creating apparent whorls.
Houstonia: Answers to key questions in Budd's Flora and Flora of Alberta leading to this genus.
Solidago: Answers to key questions in Budd's Flora leading to this family.