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An edge is a direct connection between two nodes in a a graph. It is often represented as a line, either straight or curved. The meaning of an edge depends on the context. For instance, in a phylogenetic tree, an edge typically indicates direct descent but it may also indicate reticulation such as horizontal gene transfer. An edge may be either undirected or directed. In the latter case, the direction is often shown by drawing the line as an arrow.

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