Influential yet unresolved branch points on the Open Tree of Life

The visualisation of life at shows all branch points as a split into two branches. Yet the Open Tree of Life, from whom much of the data is gathered, have many examples of large polytomies, where many branches emerge from a single point. These are almost entirely cases where a large number of species have been classified by taxonomists into a single group (say the ragworts), but where the OpenTree has not incorporated any extra studies that can resolve relationships between species within the group.

With this in mind, I thought it would be useful to look at which branches on the OpenTree show very large polytomies (hundreds or thousands of branches coming off a single point) and which are additionally influential because they are found in the ancestry of many species. So I knocked up a quick script to output the polytomy size vs number of descendant tips for each node on the OpenTree of Life. I’ve coloured plants in green, animals in red, fungi in blue, (eu)bacteria in magenta, and everything else in grey, although since the animals seem to be the last to be plotted, red is covering over the denser areas of the plot. I’ve also labelled some of the most egregious suspects – nodes with large polytomies that affect very large numbers of species.


Polytomy size against number of descendant tips in the OpenTree

If I were to focus efforts on finding phylogenies to incorporate into the OpenTree, I would try looking at the nodes labeled in the plot above.

2 thoughts on “Influential yet unresolved branch points on the Open Tree of Life

  1. Does that mean that the branch ordering in OneZoom is arbitrary in those polytomic cases?

    • Yes, absolutely. The branch ordering for polytomies is arbitrary (but consistent across tree builds). It’s a bit hacky, but may be the only way to visualize this given the fractal strcuture (there’s also the OneZoom polytomy view for those who want a less deceptive viz).

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