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Branching diagram with square corners, basic features

This style is easiest for most people to understand and encourages the fewest misconceptions. The square-cornered 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 bottom root of the tree (earlier times) towards the top tips (more recent times).
• A root at the bottom 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 upwards.  The left branch leads to ants at the top of the tree.  The right branch splits into two branches leading upwards.  The right branch of these leads to beetles at the top of the tree.  The left branch of these splits into two branches leading upwards. The left branch of these leads to flies at the top of the tree.  The righthand 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 in yellow. 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 upwards 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 upwards 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 upwards 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 with square corners, advanced features

This style is easiest for most people to understand and encourages the fewest misconceptions. The square-cornered tree shown here depicts the relationships among 9 unspecified groups of organisms. 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. 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.
• Varying branch width. One terminal tip of the tree is highlighted and expands so that it gets wider as it nears the top of the tree, forming a triangle. Varying branch width usually indicates the diversity of that lineage. Wider branches indicate greater diversity.
• Arrow or line connecting branches. A curved arrow is highlighted and leads from one interior branch of the tree to another branch. This indicates hybridization of the lineages or the sharing of genes across lineages.
• Differently colored branches. Two terminal lineages and the branching point at which they meet 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.

A button underneath the diagram is labeled “Are the branches on your tree different lengths?” and has a picture of two branches and their meeting point, on which one of the terminal branches is shorter than the other. Other buttons at the bottom are labeled “Basic tree features” and “animated video.” A button at the top is labeled “select a tree.”

Are the branches on your tree different lengths?

Two trees with square corners are shown. Both have branches of different lengths, including terminal branches of different lengths.

The first tree has a scale bar labeled “0.01 substitutions per site.”  When a tree of varying branch length has a scale bar, varying branch length represents the amount of evolutionary change that occurred in that lineage. Longer branches experienced more change.

The second tree has a vertical timescale running from 200 million years ago at the root of the tree to 0 million years ago at the top of the tree. When a tree of varying branch length has a timescale, varying branch length indicates when different lineages split or extinction events occurred. Two of the lineages on the tree have thick vertical rectangles over them. Bars placed on lineages usually indicate the time period over which fossils from that lineage are known.

A button underneath the diagram takes you back to advanced tree features. Other 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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