A character type with 2 states that follow an evolutionarily plausible sequence, e.g. petals many - 5 - 3 - 0. Changes between adjacent states are counted as one step and changes between non-adjacent states are counted as (1 + no. of skipped states), e.g. from 5 petals to 0 (or vice versa) would be 2 steps (cf. unordered, Dollo, irreversible).