Roots developed from parts of plant other than the radicle are called adventitious roots. They branch like tap roots and may be underground or aerial, and may develop from nodes, internodes or leaves, etc.
Tap roots develop from the radicle of embryo and persist and grow directly into primary root.
Fibrous roots are thin, thread-like branched roots developing from the base of stem. These are modifications of tap root, found in monocots.
Nodular roots are modifications of tap roots in which root branches develop small or large swellings called nodules. They help in nitrogen fixation.