diff --git a/README.md b/README.md
index d478be9..134a9fd 100644
--- a/README.md
+++ b/README.md
@@ -37,8 +37,7 @@ Options:
   -o, --outpath PATH       write processed seqs to this filename  [required]
   -np, --numprocs INTEGER  number of processes  [default: 1]
   -F, --force_overwrite    Overwrite existing file if it exists
-  -m, --moltype [dna|rna]  Molecular type of sequences, defaults to DNA
-                           [default: dna]
+  -m, --moltype [dna|rna]  Molecular type of sequences  [default: dna]
   -L, --limit INTEGER      number of sequences to process
   -hp, --hide_progress     hide progress bars
   --help                   Show this message and exit.
@@ -75,7 +74,7 @@ Usage: dvs nmost [OPTIONS]
   Identify n seqs that maximise average delta JSD
 
 Options:
-  -s, --seqfile PATH       path to .dvtgseqs file  [required]
+  -s, --seqfile PATH       path to .dvseqs file  [required]
   -o, --outpath PATH       the input string will be cast to Path instance
   -n, --number INTEGER     number of seqs in divergent set  [required]
   -k INTEGER               k-mer size  [default: 6]
@@ -150,11 +149,11 @@ named sequences are added to the final result.
 
 Input type
 ----------
-SequenceCollection, ArrayAlignment, Alignment
+ArrayAlignment, SequenceCollection, Alignment
 
 Output type
 -----------
-SequenceCollection, ArrayAlignment, Alignment
+ArrayAlignment, SequenceCollection, Alignment
 
 ```
 <!-- [[[end]]] -->
@@ -188,7 +187,7 @@ Usage: dvs max [OPTIONS]
   Identify the seqs that maximise average delta JSD
 
 Options:
-  -s, --seqfile PATH       path to .dvtgseqs file  [required]
+  -s, --seqfile PATH       path to .dvseqs file  [required]
   -o, --outpath PATH       the input string will be cast to Path instance
   -z, --min_size INTEGER   minimum size of divergent set  [default: 7]
   -zp, --max_size INTEGER  maximum size of divergent set
@@ -273,12 +272,222 @@ named sequences are added to the final result.
 
 Input type
 ----------
-SequenceCollection, ArrayAlignment, Alignment
+ArrayAlignment, SequenceCollection, Alignment
 
 Output type
 -----------
-SequenceCollection, ArrayAlignment, Alignment
+ArrayAlignment, SequenceCollection, Alignment
 
 ```
 <!-- [[[end]]] -->
-</details>
\ No newline at end of file
+</details>
+
+### `dvs ctree`: build a phylogeny using k-mers
+
+The result of the `ctree` command is a newick formatted tree string without distances.
+
+> **Note**
+> A fuller explanation is coming soon!
+
+<details>
+    <summary>Options for command line dvs ctree</summary>
+
+<!-- [[[cog
+import cog
+from diverse_seq.cli import main
+from click.testing import CliRunner
+runner = CliRunner()
+result = runner.invoke(main, ["ctree", "--help"])
+help = result.output.replace("Usage: main", "Usage: dvs")
+cog.out(
+    "```\n{}\n```".format(help)
+)
+]]] -->
+```
+Usage: dvs ctree [OPTIONS]
+
+  Quickly compute a cluster tree based on kmers for a collection of sequences.
+
+Options:
+  -s, --seqfile PATH              path to .dvseqs file  [required]
+  -o, --outpath PATH              the input string will be cast to Path instance
+  -m, --moltype [dna|rna]         Molecular type of sequences  [default: dna]
+  -k INTEGER                      k-mer size  [default: 6]
+  --sketch-size INTEGER           sketch size for mash distance
+  -d, --distance [mash|euclidean]
+                                  distance measure for tree construction
+                                  [default: mash]
+  -c, --canonical-kmers           consider kmers identical to their reverse
+                                  complement
+  -L, --limit INTEGER             number of sequences to process
+  -np, --numprocs INTEGER         number of processes  [default: 1]
+  -hp, --hide_progress            hide progress bars
+  --help                          Show this message and exit.
+
+```
+<!-- [[[end]]] -->
+
+</details>
+
+<details>
+    <summary>Options for cogent3 app dvs_ctree</summary>
+
+The `dvs ctree` is also available as the [cogent3 app](https://cogent3.org/doc/app/index.html) `dvs_ctree` or `dvs_par_ctree`. The latter is not composable, but can run the analysis for a single collection in parallel.
+
+<!-- [[[cog
+import cog
+import contextlib
+import io
+
+
+from cogent3 import app_help
+
+buffer = io.StringIO()
+
+with contextlib.redirect_stdout(buffer):
+  app_help("dvs_ctree")
+cog.out(
+    "```\n{}\n```".format(buffer.getvalue())
+)
+]]] -->
+```
+Overview
+--------
+Create a cluster tree from kmer distances.
+
+Options for making the app
+--------------------------
+dvs_ctree_app = get_app(
+    'dvs_ctree',
+    k=12,
+    sketch_size=3000,
+    moltype='dna',
+    distance_mode='mash',
+    mash_canonical_kmers=None,
+    show_progress=False,
+)
+
+Initialise parameters for generating a kmer cluster tree.
+
+Parameters
+----------
+k
+    kmer size
+sketch_size
+    size of sketches, only applies to mash distance
+moltype
+    seq collection molecular type
+distance_mode
+    mash distance or euclidean distance between kmer freqs
+mash_canonical_kmers
+    whether to use mash canonical kmers for mash distance
+show_progress
+    whether to show progress bars
+
+Notes
+-----
+This app is composable.
+
+If mash_canonical_kmers is enabled when using the mash distance,
+kmers are considered identical to their reverse complement.
+
+References
+----------
+.. [1] Ondov, B. D., Treangen, T. J., Melsted, P., Mallonee, A. B.,
+   Bergman, N. H., Koren, S., & Phillippy, A. M. (2016).
+   Mash: fast genome and metagenome distance estimation using MinHash.
+   Genome biology, 17, 1-14.
+
+Input type
+----------
+ArrayAlignment, SequenceCollection, Alignment
+
+Output type
+-----------
+PhyloNode
+
+```
+<!-- [[[end]]] -->
+
+
+<!-- [[[cog
+import cog
+import contextlib
+import io
+
+
+from cogent3 import app_help
+
+buffer = io.StringIO()
+
+with contextlib.redirect_stdout(buffer):
+  app_help("dvs_par_ctree")
+cog.out(
+    "```\n{}\n```".format(buffer.getvalue())
+)
+]]] -->
+```
+Overview
+--------
+Create a cluster tree from kmer distances in parallel.
+
+Options for making the app
+--------------------------
+dvs_par_ctree_app = get_app(
+    'dvs_par_ctree',
+    k=12,
+    sketch_size=3000,
+    moltype='dna',
+    distance_mode='mash',
+    mash_canonical_kmers=None,
+    show_progress=False,
+    max_workers=None,
+    parallel=True,
+)
+
+Initialise parameters for generating a kmer cluster tree.
+
+Parameters
+----------
+k
+    kmer size
+sketch_size
+    size of sketches, only applies to mash distance
+moltype
+    seq collection molecular type
+distance_mode
+    mash distance or euclidean distance between kmer freqs
+mash_canonical_kmers
+    whether to use mash canonical kmers for mash distance
+show_progress
+    whether to show progress bars
+numprocs
+    number of workers, defaults to running serial
+
+Notes
+-----
+This app is not composable but can run in parallel. It is
+best suited to a single large sequence collection.
+
+If mash_canonical_kmers is enabled when using the mash distance,
+kmers are considered identical to their reverse complement.
+
+References
+----------
+.. [1] Ondov, B. D., Treangen, T. J., Melsted, P., Mallonee, A. B.,
+   Bergman, N. H., Koren, S., & Phillippy, A. M. (2016).
+   Mash: fast genome and metagenome distance estimation using MinHash.
+   Genome biology, 17, 1-14.
+
+Input type
+----------
+ArrayAlignment, SequenceCollection, Alignment
+
+Output type
+-----------
+PhyloNode
+
+```
+<!-- [[[end]]] -->
+
+</details>
diff --git a/src/diverse_seq/cli.py b/src/diverse_seq/cli.py
index a596eb5..95ad757 100644
--- a/src/diverse_seq/cli.py
+++ b/src/diverse_seq/cli.py
@@ -457,7 +457,6 @@ def ctree(
     hide_progress: bool,
 ):
     """Quickly compute a cluster tree based on kmers for a collection of sequences."""
-
     if seqfile.suffix != ".dvseqs":
         dvs_util.print_colour(
             "Sequence data needs to be preprocessed, use 'dvs prep'",
@@ -479,7 +478,7 @@ def ctree(
         )
         sys.exit(1)
 
-    seqids = dvs_data_store.get_seqids_from_store(seqfile)[:limit]
+    seqids = dvs_data_store.get_seqids_from_store(seqfile)
     if limit is not None:
         seqids = seqids[:limit]
 
@@ -496,7 +495,11 @@ def ctree(
         show_progress=not hide_progress,
     )
     tree = app(seqids)  # pylint: disable=not-callable
-    tree.write(outpath)
+    if not tree:
+        dvs_util.print_colour(tree, "red")
+        sys.exit(1)
+
+      tree.write(outpath)
 
 
 if __name__ == "__main__":
diff --git a/src/diverse_seq/cluster.py b/src/diverse_seq/cluster.py
index 8111b04..8140e0d 100644
--- a/src/diverse_seq/cluster.py
+++ b/src/diverse_seq/cluster.py
@@ -132,6 +132,8 @@ def __init__(
 
         Notes
         -----
+        This app is composable.
+
         If mash_canonical_kmers is enabled when using the mash distance,
         kmers are considered identical to their reverse complement.
 
@@ -233,14 +235,14 @@ def make_cluster_tree(
             tree_dict.pop(right_index),
         )
         node_index += 1
-
-    tree = make_tree(str(tree_dict[node_index - 1]))
-
+    # use string representation and then remove quotes
+    treestring = str(tree_dict[node_index - 1]).replace("'", "")
+    tree = make_tree(treestring=treestring, underscore_unmunge=True)
     progress.update(tree_task, completed=1, total=1)
-
     return tree
 
 
+
 class DvsParCtreeMixin:
     def _mash_dist(self, seq_arrays: Sequence[SeqArray]) -> numpy.ndarray:
         """Calculates pairwise mash distances between sequences in parallel.
diff --git a/src/diverse_seq/distance.py b/src/diverse_seq/distance.py
index 42fb451..7d8c5d7 100644
--- a/src/diverse_seq/distance.py
+++ b/src/diverse_seq/distance.py
@@ -159,7 +159,6 @@ def mash_distances(
     numpy.ndarray
         Pairwise mash distances between sequences.
     """
-
     if progress is None:
         progress = Progress(disable=True)
 
diff --git a/tests/test_cli.py b/tests/test_cli.py
index 66b1987..cdf04c5 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -253,9 +253,7 @@ def test_ctree(
 ):
     outpath = tmp_dir / "out.tre"
 
-    args = (
-        f"-s {processed_seq_path} -o {outpath} -d {distance} -k {k} -np {max_workers}"
-    )
+    args = f"-s {processed_seq_path} -o {outpath} -d {distance} -k {k} -np {max_workers} -hp"
     if sketch_size is not None:
         args += f" --sketch-size {sketch_size}"
     args = args.split()