diff --git a/graphicle/data.py b/graphicle/data.py
index 1477cd4..c5f183c 100644
--- a/graphicle/data.py
+++ b/graphicle/data.py
@@ -914,7 +914,7 @@ def recursive_drop(
         return mask_group
 
     def flatten(
-        self, how: ty.Literal["rise", "agg"] = "rise"
+        self, how: ty.Literal["rise", "agg", "leaves"] = "rise"
     ) -> "MaskGroup[MaskArray]":
         """Removes nesting such that the ``MaskGroup`` contains only
         ``MaskArray`` instances, and no other ``MaskGroup``.
@@ -922,18 +922,23 @@ def flatten(
         .. versionadded:: 0.1.11
 
         .. versionchanged:: 0.2.6
-           Added ``'how'`` parameter.
+           Added ``how`` parameter.
+
+        .. versionchanged:: 0.3.7
+           Added ``leaves`` option for ``how`` parameter.
 
         Parameters
         ----------
-        how : {'rise', 'agg'}
-            Method used to convert into flat ``MaskGroup``. ``'rise'``
+        how : {'rise', 'agg', 'leaves'}
+            Method used to convert into flat ``MaskGroup``. ``rise``
             recurses through nested levels, raising all contained
-            ``MaskArray`` instances to the top level. ``'agg'`` loops
-            over the top level of ``MaskBase`` objects, leaving
-            top-level ``MaskArray`` objects as-is, but calling the
-            aggregation operation over any ``MaskGroup``. Default is
-            ``'rise'``.
+            ``MaskArray`` instances to the top level.
+            ``agg`` loops over the top level of ``MaskBase`` objects,
+            leaving top-level ``MaskArray`` objects as-is, but calling
+            the aggregation operation over any ``MaskGroup``.
+            ``leaves`` brings the innermosted nested ``MaskArray``
+            instances to the top level, discarding the rest.
+            Default is``'rise'``.
 
         Returns
         -------
@@ -942,7 +947,19 @@ def flatten(
             at the top level.
         """
 
-        def leaves(
+        if how == "leaves":
+            from graphicle.select import leaf_masks
+
+            return leaf_masks(self)
+        if how == "agg":
+            return self.__class__(
+                cl.OrderedDict(
+                    zip(self.keys(), map(op.attrgetter("data"), self.values()))
+                ),
+                "or",
+            )
+
+        def visit(
             mask_group: "MaskGroup",
         ) -> ty.Iterator[ty.Tuple[str, base.MaskLike]]:
             for key, val in mask_group.items():
@@ -950,18 +967,11 @@ def leaves(
                     continue
                 if isinstance(val, type(self)):
                     yield key, val.data
-                    yield from leaves(val)
+                    yield from visit(val)
                 else:
                     yield key, val
 
-        if how == "rise":
-            return self.__class__(cl.OrderedDict(leaves(self)), "or")  # type: ignore
-        return self.__class__(
-            cl.OrderedDict(
-                zip(self.keys(), map(op.attrgetter("data"), self.values()))
-            ),
-            "or",
-        )
+        return self.__class__(cl.OrderedDict(visit(self)), self.agg_op)
 
     def serialize(self) -> ty.Dict[str, ty.Any]:
         """Returns serialized data as a dictionary.