Bio Phylo Tree Visualization

Version Compatibility

Reference examples tested with: BioPython 1.83+, matplotlib 3.8+. Rich-figure alternatives: ggtree 3.12+ / treeio 1.28+ / ggtreeExtra 1.14+ (Bioconductor), ete4 4.x (Python), iTOL v6 (web), FigTree (desktop).

Before using code patterns, verify installed versions match. If versions differ:

• Python: pip show biopython then help(Phylo.draw) to check signatures
• R: packageVersion('ggtree') then ?ggtree to verify layout and geom arguments

If code throws ImportError, AttributeError, or TypeError, introspect the installed package and adapt the example to match the actual API rather than retrying.

Bio.Phylo draw() renders rectangular layouts only and parses no BEAST/MrBayes annotation block; circular/fan/unrooted layouts and HPD bars require ggtree, ETE4, or iTOL. The ETE3->ETE4 migration changed APIs; introspect rather than assume ETE3 signatures.

Tree Visualization -- A Figure Is an Argument

"Draw and export my tree figure" -> Render a topology under a chosen layout and branch-length encoding, decide which support to show and how to label it, and export in a format that survives print.

• Python quick look: Phylo.draw(tree, axes=ax) (Bio.Phylo + matplotlib)
• Publication with metadata, rich support, or BEAST HPD bars: ggtree + treeio (R)

Scope: drawing, styling, annotating, and exporting tree figures, and choosing the drawing tool. Reading/converting files and preserving [&...] annotations before plotting -> tree-io. Rooting, ladderizing, pruning, collapsing low-support nodes -> tree-manipulation. ggplot2 grammar, themes, and ggsave underlying ggtree -> data-visualization/ggplot2-fundamentals. Composing a tree plus aligned panels into one figure -> data-visualization/multipanel-figures.

The Single Most Important Modern Insight

A phylogenetic tree figure is a rhetorical and modeling artifact, not a neutral picture of the data. A Newick or Nexus file encodes a topology, optionally branch lengths, optionally one node label; it does NOT encode which child is drawn on top, whether the horizontal axis means evolutionary distance or just nesting depth, where the root sits, the aspect ratio, or which of several support measures a bare "95" refers to. Every one of those is supplied by the person drawing the tree, so the figure is the data filtered through a dozen interpretive choices the reader cannot see. Four argument-level decisions dominate, and the same file can be drawn to tell mutually contradictory stories that are all technically correct renderings of one topology:

1. The geometry is a claim about what the lengths mean. A cladogram asserts only nesting; a phylogram asserts nesting plus amount of change (substitutions per site); a chronogram asserts timing and demands a clock model plus calibrations. Drawing a phylogram as a cladogram erases rate variation, the very signal that flags long-branch attraction; drawing untrusted branch lengths as a phylogram fabricates a quantitative claim.
2. Ladderization implies a directionality that is not there. Sibling subclades are unordered, so any node rotation is the same tree, but the eye reads top-to-bottom ordering as a march of progress toward the bottom-most tip. Rotation can also bury non-monophyly: a paraphyletic group can be rotated to look contiguous, or a clean clade made to look scattered.
3. Which support is shown, and whether it is labeled, changes the conclusion. Support is not accuracy, and the measures are not interchangeable: a posterior of 0.95 is generally weaker evidence than a bootstrap of 95 for the same data, and UFBoot 95, SH-aLRT 80, and TBE live on different scales. A bare integer with no legend is the quietest lie because the reader assumes bootstrap and the ambiguity always flatters the result.
4. The drawing tool is decided by the I/O layer, not the surrounding language. If the tree carries BEAST/MrBayes HPD intervals and posteriors, only a tool whose data model can carry those annotations (treeio + ggtree) can plot them; Bio.Phylo flattens the tree to topology + length + one label and silently drops the uncertainty that was the result.

The skill's job is to make these choices conscious and DECLARE them in the caption, not to default into them. Default ladderization plus cladogram-ish rendering plus unlabeled nodes is the path of least resistance, and it is an argument the user did not intend to make.

Tool Taxonomy

The central decision is which drawing tool to reach for, and it is coupled to the I/O decision: a tool that flattens the tree to topology plus one label cannot draw BEAST HPD bars or posteriors it cannot represent. The plotting path through treeio + ggtree is the same I/O choice made in tree-io.

Decision rule: large tree or no-code web annotation -> iTOL v6. Publication figure with metadata, dual support, HPD bars, or aligned heatmaps -> ggtree + treeio (+ ggtreeExtra for circular rings). Programmatic styling of thousands of nodes or NCBI-taxonomy annotation -> ETE4. Fast topology look from a Python script -> Bio.Phylo. Interactive rooting/inspection of one BEAST tree -> FigTree, then move the reproducible figure to ggtree. The recurring mistake is defaulting to Bio.Phylo because the pipeline is Python, then discovering it cannot draw a circular layout, place a heatmap, or show the BEAST HPD bars that are the whole point.

What Each Layout Reveals and Hides

Circular is still a ROOTED tree bent into a ring (center = root = past); unrooted/radial explicitly refuses a root. Presenting an unrooted radial tree and narrating "X is basal" is a contradiction.

Bio.Phylo + matplotlib Recipes

Quick text and ASCII inspection, no figure needed:

from Bio import Phylo

tree = Phylo.read('tree.nwk', 'newick')
print(tree)                  # indented text summary
Phylo.draw_ascii(tree)       # ASCII-art diagram, useful in a terminal or log

Draw to a vector file (always pass an axes and do_show=False for headless/scripted use):

from Bio import Phylo
import matplotlib.pyplot as plt

tree = Phylo.read('tree.nwk', 'newick')
tree.ladderize()             # legibility only; ordering carries NO phylogenetic meaning -- say so in the caption

fig, ax = plt.subplots(figsize=(10, 8))
Phylo.draw(tree, axes=ax, do_show=False)
ax.set_title('Phylogenetic tree (phylogram, branch length = subs/site)')
fig.savefig('tree.pdf', bbox_inches='tight')   # vector: text and lines stay sharp at any size
plt.close(fig)

Label tips, and show support with its measure named (never a bare integer):

def tip_only(clade):
    return clade.name if clade.is_terminal() else ''

def support_label(clade):
    # the measure MUST be stated in the legend/caption; here values are bootstrap percentages
    if not clade.is_terminal() and clade.confidence is not None:
        return f'{clade.confidence:.0f}'
    return ''

fig, ax = plt.subplots(figsize=(12, 10))
Phylo.draw(tree, axes=ax, do_show=False, label_func=tip_only, branch_labels=support_label)
ax.set_title('Bootstrap support shown at internal nodes')
fig.savefig('supported_tree.svg', bbox_inches='tight')
plt.close(fig)

Color branches by group (convert to phyloXML for native color support):

from Bio.Phylo.PhyloXML import BranchColor

xtree = tree.as_phyloxml()                     # phyloXML carries branch color through draw()
for clade in xtree.find_clades():
    if clade.name and clade.name.startswith('Homo'):
        clade.color = BranchColor.from_name('red')

fig, ax = plt.subplots(figsize=(10, 8))
Phylo.draw(xtree, axes=ax, do_show=False)
fig.savefig('colored_tree.pdf', bbox_inches='tight')
plt.close(fig)

Scale the panel to tip count so labels stay legible, and drop the axis frame:

n_tips = len(tree.get_terminals())
height = max(8, n_tips * 0.25)                  # ~0.25 in/tip keeps ~6-8 pt labels from colliding

fig, ax = plt.subplots(figsize=(10, height))
Phylo.draw(tree, axes=ax, do_show=False)
ax.axis('off')
fig.savefig('scaled_tree.pdf', bbox_inches='tight')
plt.close(fig)

For circular/fan/unrooted layouts, metadata heatmaps, dual support, or BEAST HPD bars, Bio.Phylo cannot help -- route to ggtree + treeio (R), ETE4, or iTOL.

Per-Method Failure Modes

Drawing Meaningless Branch Lengths as a Phylogram

Trigger: Rendering a constraint tree, a supertree, or a tree whose lengths are non-comparable with the horizontal axis proportional to length. Mechanism: The phylogram geometry asserts a quantitative claim about evolutionary distance that the lengths do not support. Symptom: A topology-only or arbitrary-length tree appears to make precise distance statements. Fix: Draw as a cladogram and SAY so (branch.length='none' in ggtree); or, if lengths are real, keep them and state the unit (subs/site vs time) plus a scale bar.

Unlabeled or Mislabeled Support

Trigger: A node shows "98" with no legend, or two measures are printed without saying which is which. Mechanism: The reader defaults to assuming bootstrap, but it may be a posterior (much weaker for the same number), an SH-aLRT (cutoff 80), a UFBoot (cutoff 95, not the BP-70 scale), or a TBE. Symptom: A weakly resolved bush reads as a confident comb because the displayed number is over-read. Fix: Always state the measure(s) and their order (e.g. "SH-aLRT/UFBoot" at each node); collapse nodes below threshold into polytomies rather than drawing fake resolution, since bootstrap, posterior, SH-aLRT, and UFBoot sit on different scales.