Stanford
X-Trees

Internal Branches

INTERNAL BRANCHES. Quercus lobata, Valley oak.
East Oval Grove.
Photo: Noah Rosenberg, April 27, 2018

Phylogenetic trees consist of edges, or branches, and vertices, or nodes. Nodes can be leaf nodes at the tips of the tree, or internal nodes. Branches attached to leaf nodes are external branches, and all other branches are internal branches. When all leaves and the external branches immediately connected to them are pruned from a tree, only internal branches and internal nodes remain.

 

 INTERNAL BRANCHES. Eucalyptus cladocalyx, Sugar gum.
Intersection of Lomita Drive and Campus Drive.
Photo: Noah Rosenberg, November 13, 2018

In analyzing probability models for gene trees given species trees, probabilities are often computed for the pattern describing several of the most important internal branches (Rosenberg (2013),). The pattern nearer the leaves is of lesser concern, so that the key issue is whether the tree contains a specific set of internal branches near its root. More than for most campus trees, for the sugar gums located near the intersection of Palm Drive and Campus Drive, the main internal branches are largely unobscured by the leaves, so that the deepest structure of the tree is easily observed. The pattern is accentuated in this specimen by the distorted light due to California wildfires.