Bidens frondosa and Bidens tripartita are rather similar plants. Different are mainly the fruits, which have a rough surface at Bidens frondosa, while the fruits of Bidens tripartita are smooth.
As long as the Beggartick hasn't fruit, the best attribute to differ Bidens tripartita from Bidens frondosa is, that at Bidens tripartita the leaves are going along their stems, while at Bidens frondosa they clearly end where the stem starts. The blossoms of Bidens tripartita tend to be somewhat wider that those of Bidens frondosa.