True or false? the absence of a trait cannot be used as a synapomorphy in phylogenetic analysis, only shared derived traits that are present in the clade can be used.

This statement is False.

Explanation:

A shared apo-morphy which differentiate a clade from other organisms is called synapomorphy. In simple words, members of monophyletic group shares an apomorphy which indicate the presence or absence of certain organs from clade.

For example, loss of legs in snakes is an important  synapomorphy.