Complex sentence: If the entire key consists of exactly two choices at each branching point, the key is called dichotomous, otherwise it is described as polytomous (or, in false analogy, "polychotomous").
Split into simpler sentences: If the entire key consists of exactly two choices at each branching point, the key is called dichotomous. If not, it is described as polytomous (or, in false analogy, "polychotomous").