A monophyletic group is defined as:
Cladogram represents phylogenetic relationships based on shared derived characters or synapomorphies defining monophyletic clades including ancestor and all descendants. Homologous synapomorphies indicate common ancestry, while homoplasy from convergent evolution misleads. Parsimony and molecular data reconstruct trees. Monophyletic, paraphyletic and polyphyletic groups distinguished. Tree thinking clarifies that cladograms show relative relationships, not necessarily time scale. Hence Group sharing common ancestor and all descendants denotes key concept in cladistics and phylogenetic inference. This concept integrates genetics, ecology and molecular evidence, frequently tested in NEET, GATE and CSIR-NET, highlighting links between genotype, phenotype and environment.
Ref: Nei & Kumar, Molecular Evolution, Clocks and Purifying Selection.