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How can rooted and unrooted (phylogenetic) trees be distinguished from one another

up vote 14 down vote favorite

I understand that both are similar in structure

But how can they be easily identified as one or the other?

Is it simply based on the presence or lack of a named root (the root is identified as a particular ancestor) or outgroup?

2 Answers

up vote 4 down vote accept

In case of a drawn figure, either look for the a short stem to the left, or for an explicitly labelled outgroup. Trees derived from phylogenetic analyses are normally unrooted by default, you need to root them by either making an arbitrary (but hopefully informed) decision or by adding an outgroup.

up vote 3 down vote

Trees can not be distinguished from each other because every unrooted tree can be made rooted by adding a root and vice versa by deletion.

If you mean dendrograms... the root is always the one node where the distance to each leaf is the same. But I don't know of an unrooted dendrogram.


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How can rooted and unrooted (phylogenetic) trees be distinguished from one another

up vote 14 down vote

I understand that both are similar in structure

But how can they be easily identified as one or the other?

Is it simply based on the presence or lack of a named root (the root is identified as a particular ancestor) or outgroup?


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up vote 9 down vote

In case of a drawn figure, either look for the a short stem to the left, or for an explicitly labelled outgroup. Trees derived from phylogenetic analyses are normally unrooted by default, you need to root them by either making an arbitrary (but hopefully informed) decision or by adding an outgroup.

edit

So when you say root it by making an arbitrary decision, does that mean labeling a particular ancestral individual as a root? Also, does this consider midpoint rooting? - arcyqwerty Dec 15 '11 at 8:43

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