Respuesta :
When making a dichotomous key, the questions you are asking have to be specific enough to seperate into two groups. A problem could arise if they are vague, as it would be confusing and the classification may turn out wrong!
It is difficult to use a dichotomous key in the following cases:
a) It becomes difficult to identify species with in the dichotomous key if the taxas included in the dichotomous key are not associated with the species in any way
b) The second difficulty could be because of presence of similar texas with in the dichotomous key which make the recognition of species difficult.