diff --git a/src/pycea/tl/ancestral_states.py b/src/pycea/tl/ancestral_states.py
index acccebd..3826f61 100755
--- a/src/pycea/tl/ancestral_states.py
+++ b/src/pycea/tl/ancestral_states.py
@@ -193,6 +193,24 @@ def _reconstruct_sum(tree: nx.DiGraph, key: str, index: int | None, fixed_nodes:
         _set_node_value(tree, node, key, sum(valid) if valid else None, index)
 
 
+def _reconstruct_sum_array(tree: nx.DiGraph, key: str, fixed_nodes: set | None = None) -> None:
+    """Reconstructs ancestral states by vectorized numpy sum over array-valued attributes."""
+    for node in reversed(list(nx.topological_sort(tree))):
+        is_fixed = fixed_nodes is not None and node in fixed_nodes
+        if tree.out_degree(node) == 0 or is_fixed:
+            continue
+        child_arrays = [tree.nodes[child][key] for child in tree.successors(node)]
+        stacked = np.stack(child_arrays)
+        result = np.nansum(stacked, axis=0)
+        result[np.all(np.isnan(stacked), axis=0)] = np.nan
+        tree.nodes[node][key] = result
+    # Convert numpy arrays back to lists for compatibility
+    for node in tree.nodes:
+        val = tree.nodes[node].get(key)
+        if isinstance(val, np.ndarray):
+            tree.nodes[node][key] = val.tolist()
+
+
 def _reconstruct_mean(tree: nx.DiGraph, key: str, index: int | None, fixed_nodes: set | None = None) -> None:
     """Reconstructs ancestral by averaging the values of the children."""
 
@@ -387,18 +405,26 @@ def ancestral_states(
         # If array add to tree as list
         if is_array:
             length = data.shape[1]
-            node_attrs = data.apply(lambda row: list(row), axis=1).to_dict()
-            for node in t.nodes:
-                if node not in node_attrs:
-                    node_attrs[node] = [None] * length
-            _remove_node_attributes(t, keys_added[0])
-            nx.set_node_attributes(t, node_attrs, keys_added[0])
             fixed_nodes = None
             if tdata.alignment != "leaves":
                 not_all_nan = ~data.isna().all(axis=1)
                 fixed_nodes = set(data[not_all_nan].index) - leaves_set
-            for index in range(length):
-                _ancestral_states(t, keys_added[0], method, costs, missing_state, default_state, index, fixed_nodes)
+            _remove_node_attributes(t, keys_added[0])
+            if method == "sum":
+                node_attrs = dict(zip(data.index, data.to_numpy(dtype=float)))
+                for node in t.nodes:
+                    if node not in node_attrs:
+                        node_attrs[node] = np.full(length, np.nan)
+                nx.set_node_attributes(t, node_attrs, keys_added[0])
+                _reconstruct_sum_array(t, keys_added[0], fixed_nodes)
+            else:
+                node_attrs = data.apply(lambda row: list(row), axis=1).to_dict()
+                for node in t.nodes:
+                    if node not in node_attrs:
+                        node_attrs[node] = [None] * length
+                nx.set_node_attributes(t, node_attrs, keys_added[0])
+                for index in range(length):
+                    _ancestral_states(t, keys_added[0], method, costs, missing_state, default_state, index, fixed_nodes)
         # If column add to tree as scalar
         else:
             for key, key_added in zip(keys, keys_added, strict=False):