How does a dichotomous key identify unknown you identify unknown specimens based on their traits?

A dichotomous key helps us classify organisms using their physical characteristics by dividing the organisms in to groups. For example, organisms with 6 legs, organisms with 8 legs and organisms with more than 8 legs are all grouped into different categories. These categories may further be divided into more categories; for example, the on the basis of the organisms' mode of respiration or on the basis of the organisms' body structures.
The groupings help in identification, separation and classification of organisms.

C. a mature ovule of a plant.