Kladogrammi

Kladogrammi, or cladogram in English, is a branching diagram used in cladistics to illustrate hypotheses about evolutionary relationships among organisms or other taxa. In a kladogram, internal nodes represent hypothetical common ancestors and the branching pattern reflects the order in which lineages split.

A key feature is that the diagram conveys branching order (topology) rather than precise time or amount of change. Closely related groups share more recent common ancestors, and clade names are used for monophyletic groups defined by shared derived characteristics.

Construction relies on characters and synapomorphies. Researchers identify derived traits that unite certain taxa, root the diagram with an outgroup to determine character polarity, and then group taxa into nested clades. The resulting kladogram is a hypothesis subject to new evidence and reinterpretation.

Origins and usage: the method was formalized by Willi Hennig in the mid-20th century and has become central to modern systematics, paleontology, and comparative biology. Kladograms are widely used in teaching and as frameworks for interpreting evolutionary data.

Relation to phylogenetic trees: while a cladogram emphasizes branching order, some diagrams are drawn with branch lengths that imply time or amount of change, but by convention many cladograms use equal lengths or omit lengths. Rooting the diagram requires an outgroup or other information; some diagrams are unrooted and only show relationships without direction.

Limitations: inferences depend on chosen characters and scoring; convergent evolution and reversals (homoplasy) can confound signals; incomplete sampling can produce ambiguous relationships. As such, kladograms represent current best hypotheses rather than definitive histories.