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Branching diagram arranged in a circle with root at the center, basic features

This style is often used for large trees with hundreds of species, but can be difficult to read. The circular tree shown here depicts the relationships among ants, flies, butterflies, and beetles. This diagram has the following basic features:

• An arrow showing that evolutionary time flows from the root of the tree at the center (earlier times) towards the tips on the outside of the circle (more recent times).
• A root in the center from which the other branches emanate. The root represents the ancestor that all the lineages on the tree have in common.
• A branching pattern. The branching pattern of this tree shows two branches emanating from the root of the tree leading outwards.  The bottom branch leads to ants at the outside edge of the tree.  The right branch splits into two branches leading outwards.  The right branch of these leads to beetles at the top of the tree.  The left branch of these splits into two branches leading outwards. The bottom branch of these leads to flies at the outside edge of the tree.  The top branch of these leads to butterflies at the top of the tree. The branching pattern represents evolutionary relationships. It tells you how closely related different groups are. Here, flies and butterflies are more closely related to each other than either is to beetles because their branches join more recently than either joins the beetles’ branch. All the insect groups are related to one another, but some are more closely related than others.
• Branching points. Branching points represent the ancestor that all the lineages whose branches join at that point have in common. Three branching points on the tree are highlighted. Point 1 appears over the point at which the fly and butterfly branches meet.  When you click it, that point and the two branches emanating outwards from it (the fly and butterfly branches) are highlighted. Point 2 appears over the point at which the beetle branch connects to the shared ancestral branch of flies and butterflies. When you click it, that point and all the branches emanating outwards from it (including the fly, butterfly, and beetle branches) are highlighted. Point 3 appears over the point at which the ant branch connects to the shared ancestral branch of flies, butterflies, and beetles. When you click it, that point and all the branches emanating outwards from it (including the ant, fly, butterfly, and beetle branches) are highlighted. Here, point 1 is the most recent ancestor that flies and butterflies have in common. Point 2 is the ancestor that flies, butterflies, and beetles have in common. Point 3 is the ancestor that all the lineages have in common.
• Tips represent groups of organisms. On the tree, the icons depicting ants, flies, butterflies, and beetles are each highlighted. Here, each tip is a major group of insects.

Buttons at the bottom are labeled “advanced tree features” and “animated video.” A button at the top is labeled “select a tree.”

Branching diagram arranged in a circle with root at the center, advanced features

This style is often used for large trees with hundreds of species, but can be difficult to read. The circular tree shown here depicts the relationships among 14 unspecified groups. This diagram has the following advanced features:

• Highlighted group or name on a lineage. “Name of group” is boxed, highlighted, and appears on an interior branch of the tree. A set of three terminal tips is also labeled “name of group.” When a name is written on a lineage, it indicates that the lineages descending from that lineage all belong to the same named group.
• Labeled branch mark. One vertical lineage on the tree has a short horizontal line on it that is labeled “dark wings evolve.” This indicates that a particular feature (such as having dark- instead of light-colored wings) evolved and was inherited by the descendent lineages, the lineages that have that ancestor in common.
• A polytomy is represented by three or more lineages coming from the same branching point. A branching point from which three branches all directly emanate (one going to the left, one going straight up, and one going to the right) is highlighted along with those descendant lineages. A polytomy indicates that scientists are uncertain about which of those lineages are more closely related.
• Differently colored branches. Three terminal lineages and the branching point to which they all trace back are colored red, instead of black as the rest of the branches on the tree are. This usually indicates that a particular feature evolved and was inherited by the highlighted lineages. It can also mean that the highlighted branches share the same name.
• Numbers at branching point. One branching point is labeled “85” and this number is highlighted. This indicates how confident scientists are in the relationships shown at that point. Higher numbers mean greater confidence. Depending on the statistic used, the numbers may fall between 0 and 100 or between 0 and close to 1.
• Images near different branches. Three segments of a single lineage on the tree have drawings of a beetle near them, which are highlighted. The lowest beetle is the largest and the beetle highest on the tree is the smallest. This can indicate hypotheses about what ancestors looked like or what traits they had.
• Varying branch length with scale bar. Scale bar is labeled “0.01 substitutions per site.” Branch length represents the amount of evolutionary change that occurred in that lineage. Longer branches experienced more change.

Buttons at the bottom are labeled “Basic tree features” and “animated video.” A button at the top is labeled “select a tree.”

Animated video

An animated video shows these different styles of branching diagram morphing into another. Each diagram depicts the relationships among ants, flies, butterflies, and beetles. All evolutionary trees, no matter what they look like, represent the same thing: evolutionary relationships.

Buttons at the bottom are labeled “basic tree features” and “advanced tree features.” A button at the top is labeled “select a tree.”

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