diff --git a/intake_esm/core.py b/intake_esm/core.py
index acae149..13fa719 100644
--- a/intake_esm/core.py
+++ b/intake_esm/core.py
@@ -1,6 +1,8 @@
+import concurrent.futures
 import json
 import logging
-from collections import namedtuple
+from collections import OrderedDict, namedtuple
+from copy import deepcopy
 from typing import Any, Dict, List, Tuple, Union
 from warnings import warn
 
@@ -107,14 +109,33 @@ class esm_datastore(intake.catalog.Catalog):
         self._log_level = log_level
         self._datasets = {}
         self.sep = sep
+        self._data_format, self._format_column_name = None, None
+        self._path_column_name = self.esmcol_data['assets']['column_name']
+        if 'format' in self.esmcol_data['assets']:
+            self._data_format = self.esmcol_data['assets']['format']
+        else:
+            self._format_column_name = self.esmcol_data['assets']['format_column_name']
         self.aggregation_info = self._get_aggregation_info()
         self._entries = {}
         self._set_groups_and_keys()
         super(esm_datastore, self).__init__(**kwargs)
 
     def _set_groups_and_keys(self):
-        self._grouped = self.df.groupby(self.aggregation_info.groupby_attrs)
-        self._keys = list(self._grouped.groups.keys())
+        if self.aggregation_info.groupby_attrs and set(self.df.columns) != set(
+            self.aggregation_info.groupby_attrs
+        ):
+            self._grouped = self.df.groupby(self.aggregation_info.groupby_attrs)
+            internal_keys = self._grouped.groups.keys()
+            public_keys = [self.sep.join(str(v) for v in x) for x in internal_keys]
+
+        else:
+            self._grouped = self.df
+            internal_keys = list(self._grouped.index)
+            public_keys = [
+                self.sep.join(str(v) for v in row.values) for _, row in self._grouped.iterrows()
+            ]
+
+        self._keys = dict(zip(public_keys, internal_keys))
 
     def _allnan_or_nonan(self, column: str) -> bool:
         """
@@ -153,46 +174,27 @@ class esm_datastore(intake.catalog.Catalog):
                 'aggregations',
                 'agg_columns',
                 'aggregation_dict',
-                'path_column_name',
-                'data_format',
-                'format_column_name',
             ],
         )
 
         groupby_attrs = []
-        data_format = None
-        format_column_name = None
         variable_column_name = None
         aggregations = []
         aggregation_dict = {}
         agg_columns = []
-        path_column_name = self.esmcol_data['assets']['column_name']
-
-        if 'format' in self.esmcol_data['assets']:
-            data_format = self.esmcol_data['assets']['format']
-        else:
-            format_column_name = self.esmcol_data['assets']['format_column_name']
 
         if 'aggregation_control' in self.esmcol_data:
             variable_column_name = self.esmcol_data['aggregation_control']['variable_column_name']
             groupby_attrs = self.esmcol_data['aggregation_control'].get('groupby_attrs', [])
             aggregations = self.esmcol_data['aggregation_control'].get('aggregations', [])
             aggregations, aggregation_dict, agg_columns = _construct_agg_info(aggregations)
+            groupby_attrs = list(filter(self._allnan_or_nonan, groupby_attrs))
 
-        if not groupby_attrs:
-            groupby_attrs = self.df.columns.tolist()
-
-        groupby_attrs = list(filter(self._allnan_or_nonan, groupby_attrs))
+        elif not groupby_attrs or 'aggregation_control' not in self.esmcol_data:
+            groupby_attrs = []
 
         aggregation_info = AggregationInfo(
-            groupby_attrs,
-            variable_column_name,
-            aggregations,
-            agg_columns,
-            aggregation_dict,
-            path_column_name,
-            data_format,
-            format_column_name,
+            groupby_attrs, variable_column_name, aggregations, agg_columns, aggregation_dict,
         )
         return aggregation_info
 
@@ -205,8 +207,7 @@ class esm_datastore(intake.catalog.Catalog):
         list
             keys for the catalog entries
         """
-        keys = [self.sep.join(x) for x in self._keys]
-        return keys
+        return self._keys.keys()
 
     @property
     def key_template(self) -> str:
@@ -218,7 +219,11 @@ class esm_datastore(intake.catalog.Catalog):
         str
           string template used to create catalog entry keys
         """
-        return self.sep.join(self.aggregation_info.groupby_attrs)
+        if self.aggregation_info.groupby_attrs:
+            template = self.sep.join(self.aggregation_info.groupby_attrs)
+        else:
+            template = self.sep.join(self.df.columns)
+        return template
 
     @property
     def df(self) -> pd.DataFrame:
@@ -249,6 +254,7 @@ class esm_datastore(intake.catalog.Catalog):
         groupby_attrs = list(filter(self._allnan_or_nonan, value))
         self.aggregation_info = self.aggregation_info._replace(groupby_attrs=groupby_attrs)
         self._set_groups_and_keys()
+        self._entries = {}
 
     @property
     def variable_column_name(self) -> str:
@@ -282,11 +288,11 @@ class esm_datastore(intake.catalog.Catalog):
         """
         The name of the column containing the path to the asset.
         """
-        return self.aggregation_info.path_column_name
+        return self._path_column_name
 
     @path_column_name.setter
     def path_column_name(self, value: str) -> None:
-        self.aggregation_info = self.aggregation_info._replace(path_column_name=value)
+        self._path_column_name = value
 
     @property
     def data_format(self) -> str:
@@ -294,22 +300,22 @@ class esm_datastore(intake.catalog.Catalog):
         The data format. Valid values are netcdf and zarr.
         If specified, it means that all data assets in the catalog use the same data format.
         """
-        return self.aggregation_info.data_format
+        return self._data_format
 
     @data_format.setter
     def data_format(self, value: str) -> None:
-        self.aggregation_info = self.aggregation_info._replace(data_format=value)
+        self._data_format = value
 
     @property
     def format_column_name(self) -> str:
         """
         Name of the column which contains the data format.
         """
-        return self.aggregation_info.format_column_name
+        return self._format_column_name
 
     @format_column_name.setter
     def format_column_name(self, value: str) -> None:
-        self.aggregation_info = self.aggregation_info._replace(format_column_name=value)
+        self._format_column_name = value
 
     def __len__(self):
         return len(self.keys())
@@ -353,9 +359,31 @@ class esm_datastore(intake.catalog.Catalog):
             return self._entries[key]
         except KeyError:
             if key in self.keys():
-                _key = tuple(key.split(self.sep))
-                df = self._grouped.get_group(_key)
-                self._entries[key] = _make_entry(key, df, self.aggregation_info)
+                internal_key = self._keys[key]
+                if isinstance(self._grouped, pd.DataFrame):
+                    df = self._grouped.loc[internal_key]
+                    args = dict(
+                        key=key,
+                        row=df,
+                        path_column=self.path_column_name,
+                        data_format=self.data_format,
+                        format_column=self.format_column_name,
+                    )
+                    entry = _make_entry(key, 'esm_single_source', args)
+                else:
+                    df = self._grouped.get_group(internal_key)
+                    args = dict(
+                        df=df,
+                        aggregation_dict=self.aggregation_info.aggregation_dict,
+                        path_column=self.path_column_name,
+                        variable_column=self.aggregation_info.variable_column_name,
+                        data_format=self.data_format,
+                        format_column=self.format_column_name,
+                        key=key,
+                    )
+                    entry = _make_entry(key, 'esm_group', args)
+
+                self._entries[key] = entry
                 return self._entries[key]
             raise KeyError(key)
 
@@ -673,6 +701,7 @@ class esm_datastore(intake.catalog.Catalog):
         preprocess: Dict[str, Any] = None,
         storage_options: Dict[str, Any] = None,
         progressbar: bool = None,
+        aggregate: bool = None,
     ) -> Dict[str, xr.Dataset]:
         """
         Load catalog entries into a dictionary of xarray datasets.
@@ -685,14 +714,14 @@ class esm_datastore(intake.catalog.Catalog):
             Keyword arguments to pass to :py:func:`~xarray.open_dataset` function
         preprocess : callable, optional
             If provided, call this function on each dataset prior to aggregation.
-        aggregate : bool, optional
-            If "False", no aggregation will be done.
         storage_options : dict, optional
             Parameters passed to the backend file-system such as Google Cloud Storage,
             Amazon Web Service S3.
         progressbar : bool
             If True, will print a progress bar to standard error (stderr)
             when loading assets into :py:class:`~xarray.Dataset`.
+        aggregate : bool, optional
+            If False, no aggregation will be done.
 
         Returns
         -------
@@ -725,9 +754,6 @@ class esm_datastore(intake.catalog.Catalog):
             pr         (member_id, time, lat, lon) float32 dask.array<chunksize=(1, 600, 160, 320), meta=np.ndarray>
         """
 
-        import concurrent.futures
-        from collections import OrderedDict
-
         # Return fast
         if not self.keys():
             warn('There are no datasets to load! Returning an empty dictionary.')
@@ -739,7 +765,7 @@ class esm_datastore(intake.catalog.Catalog):
             preprocess=preprocess,
             storage_options=storage_options,
         )
-        token = dask.base.tokenize(source_kwargs)
+        token = dask.base.tokenize([source_kwargs, aggregate])
         if progressbar is not None:
             self.progressbar = progressbar
 
@@ -749,8 +775,12 @@ class esm_datastore(intake.catalog.Catalog):
         # Avoid re-loading data if nothing has changed since the last call
         if self._datasets and (token == self._to_dataset_args_token):
             return self._datasets
-
         self._to_dataset_args_token = token
+
+        if aggregate is not None and not aggregate:
+            self = deepcopy(self)
+            self.groupby_attrs = []
+
         if self.progressbar:
             print(
                 f"""\n--> The keys in the returned dictionary of datasets are constructed as follows:\n\t'{self.key_template}'"""
@@ -761,37 +791,26 @@ class esm_datastore(intake.catalog.Catalog):
 
         sources = [source(**source_kwargs) for _, source in self.items()]
 
+        progress, total = None, None
         if self.progressbar:
             total = len(sources)
             progress = progress_bar(range(total))
 
         with concurrent.futures.ThreadPoolExecutor(max_workers=len(sources)) as executor:
             future_tasks = [executor.submit(_load_source, source) for source in sources]
-
             for i, task in enumerate(concurrent.futures.as_completed(future_tasks)):
                 ds = task.result()
                 self._datasets[ds.attrs['intake_esm_dataset_key']] = ds
                 if self.progressbar:
                     progress.update(i)
-
             if self.progressbar:
                 progress.update(total)
-
             return self._datasets
 
 
-def _make_entry(key, df, aggregation_info):
-    args = dict(
-        df=df,
-        aggregation_dict=aggregation_info.aggregation_dict,
-        path_column=aggregation_info.path_column_name,
-        variable_column=aggregation_info.variable_column_name,
-        data_format=aggregation_info.data_format,
-        format_column=aggregation_info.format_column_name,
-        key=key,
-    )
+def _make_entry(key: str, driver: str, args: dict):
     entry = intake.catalog.local.LocalCatalogEntry(
-        name=key, description='', driver='esm_group', args=args, metadata={}
+        name=key, description='', driver=driver, args=args, metadata={}
     )
     return entry.get()
 
diff --git a/intake_esm/merge_util.py b/intake_esm/merge_util.py
index 9540faf..7477fcd 100644
--- a/intake_esm/merge_util.py
+++ b/intake_esm/merge_util.py
@@ -229,7 +229,7 @@ def _aggregate(
     return apply_aggregation(v)
 
 
-def _open_asset(path, data_format, zarr_kwargs, cdf_kwargs, preprocess, varname):
+def _open_asset(path, data_format, zarr_kwargs, cdf_kwargs, preprocess, varname=None):
     protocol = None
     root = path
     if isinstance(path, fsspec.mapping.FSMap):
@@ -259,8 +259,8 @@ def _open_asset(path, data_format, zarr_kwargs, cdf_kwargs, preprocess, varname)
         except Exception as e:
             logger.error(f'Failed to open netCDF/HDF dataset with cdf_kwargs={cdf_kwargs}')
             raise e
-
-    ds.attrs['intake_esm_varname'] = varname
+    if varname:
+        ds.attrs['intake_esm_varname'] = varname
 
     if preprocess is None:
         return ds
diff --git a/intake_esm/source.py b/intake_esm/source.py
index 7b3e3e1..d20b787 100644
--- a/intake_esm/source.py
+++ b/intake_esm/source.py
@@ -1,12 +1,88 @@
 import copy
 
+import pandas as pd
 from intake.source.base import DataSource, Schema
 
-from .merge_util import _aggregate, _path_to_mapper, _to_nested_dict
+from .merge_util import _aggregate, _open_asset, _path_to_mapper, _to_nested_dict
 
 _DATA_FORMAT_KEY = '_data_format_'
 
 
+class ESMDataSource(DataSource):
+    version = '1.0'
+    container = 'xarray'
+    name = 'esm_single_source'
+    partition_access = True
+
+    def __init__(
+        self,
+        key,
+        row,
+        path_column,
+        data_format=None,
+        format_column=None,
+        cdf_kwargs=None,
+        zarr_kwargs=None,
+        storage_options=None,
+        preprocess=None,
+        **kwargs,
+    ):
+        super().__init__(**kwargs)
+        self.key = key
+        self.cdf_kwargs = cdf_kwargs or {'chunks': {}}
+        self.zarr_kwargs = zarr_kwargs or {}
+        self.storage_options = storage_options or {}
+        self.preprocess = preprocess
+        if not isinstance(row, pd.Series) or row.empty:
+            raise ValueError('`row` must be a non-empty pandas.Series')
+        self.row = row.copy()
+        self.path_column = path_column
+        self._ds = None
+        if format_column is not None:
+            self.data_format = self.row[format_column]
+        elif data_format:
+            self.data_format = data_format
+        else:
+            raise ValueError('Please specify either `data_format` or `format_column`')
+
+    def __repr__(self):
+        return f'<name: {self.key}, asset: 1'
+
+    def _get_schema(self):
+
+        if self._ds is None:
+            self._open_dataset()
+
+            metadata = {
+                'dims': dict(self._ds.dims),
+                'data_vars': {k: list(self._ds[k].coords) for k in self._ds.data_vars.keys()},
+                'coords': tuple(self._ds.coords.keys()),
+            }
+            self._schema = Schema(
+                datashape=None, dtype=None, shape=None, npartitions=None, extra_metadata=metadata,
+            )
+        return self._schema
+
+    def _open_dataset(self):
+        mapper = _path_to_mapper(self.row[self.path_column], self.storage_options)
+        ds = _open_asset(
+            mapper, self.data_format, self.zarr_kwargs, self.cdf_kwargs, self.preprocess
+        )
+        ds.attrs['intake_esm_dataset_key'] = self.key
+        self._ds = ds
+        return ds
+
+    def to_dask(self):
+        """Return xarray object (which will have chunks)"""
+        self._load_metadata()
+        return self._ds
+
+    def close(self):
+        """Delete open files from memory"""
+        self._ds = None
+        self._schema = None
+
+
 class ESMGroupDataSource(DataSource):
     version = '1.0'
     container = 'xarray'
@@ -35,7 +111,7 @@ class ESMGroupDataSource(DataSource):
         self.storage_options = storage_options or {}
         self.preprocess = preprocess
         self._ds = None
-        if df.empty:
+        if not isinstance(df, pd.DataFrame) or df.empty:
             raise ValueError('`df` must be a non-empty pandas.DataFrame')
         self.df = df.copy()
         self.aggregation_columns, self.aggregation_dict = _sanitize_aggregations(
diff --git a/setup.py b/setup.py
index 43a4543..c6b3060 100644
--- a/setup.py
+++ b/setup.py
@@ -53,6 +53,7 @@ setup(
         'intake.drivers': [
             'esm_datastore = intake_esm.core:esm_datastore',
             'esm_group = intake_esm.source:ESMGroupDataSource',
+            'esm_single_source = intake_esm.source:ESMDataSource',
         ]
     },
     keywords='intake, xarray, catalog',

diff --git a/tests/test_source.py b/tests/test_source.py
index 921b685..938077c 100644
--- a/tests/test_source.py
+++ b/tests/test_source.py
@@ -1,11 +1,12 @@
 import os
 
+import dask
 import pandas as pd
 import pytest
 import xarray as xr
 
 from intake_esm.search import search
-from intake_esm.source import ESMGroupDataSource
+from intake_esm.source import ESMDataSource, ESMGroupDataSource
 
 
 @pytest.fixture(scope='module')
@@ -48,6 +49,7 @@ def test_esm_group(df, aggregation_dict):
     source = ESMGroupDataSource(**args)
     assert source._ds is None
     ds = source.to_dask()
+    assert dask.is_dask_collection(ds['tasmax'])
     assert ds.attrs['intake_esm_dataset_key'] == 'foo'
     assert isinstance(ds, xr.Dataset)
     assert set(subset_df['member_id']) == set(ds['member_id'].values)
@@ -55,11 +57,11 @@ def test_esm_group(df, aggregation_dict):
     assert source._ds is None
 
 
-def test_esm_group_empty_df(df, aggregation_dict):
-    empty_df = pd.DataFrame(columns=df.columns)
+@pytest.mark.parametrize('x', [pd.DataFrame(), pd.Series(dtype='object'), {}, None])
+def test_esm_group_invalid_df(x):
     args = dict(
         key='foo',
-        df=empty_df,
+        df=x,
         aggregation_dict=aggregation_dict,
         path_column='path',
         variable_column='variable_id',
@@ -70,3 +72,38 @@ def test_esm_group_empty_df(df, aggregation_dict):
 
     with pytest.raises(ValueError, match=r'`df` must be a non-empty pandas.DataFrame'):
         _ = ESMGroupDataSource(**args)
+
+
+def test_esm_single_source(df):
+    args = dict(
+        key='foo',
+        row=df.iloc[0],
+        path_column='path',
+        data_format='netcdf',
+        format_column=None,
+        cdf_kwargs={'chunks': {'time': 2}},
+    )
+
+    source = ESMDataSource(**args)
+    assert source._ds is None
+    ds = source.to_dask()
+    assert dask.is_dask_collection(ds['tasmax'])
+    assert ds.attrs['intake_esm_dataset_key'] == 'foo'
+    assert isinstance(ds, xr.Dataset)
+    source.close()
+    assert source._ds is None
+
+
+@pytest.mark.parametrize('row', [pd.DataFrame(), pd.Series(dtype='object'), {}, None])
+def test_esm_single_source_invalid_row(row):
+    args = dict(
+        key='foo',
+        row=row,
+        path_column='path',
+        data_format='netcdf',
+        format_column=None,
+        cdf_kwargs={'chunks': {'time': 2}},
+    )
+
+    with pytest.raises(ValueError, match=r'`row` must be a non-empty pandas.Series'):
+        _ = ESMDataSource(**args)

Missing `aggreagate` kwarg for `esm_datastore.to_dataset_dict`
When passing `aggregate=False` to `.to_dataset_dict` I get the following error:

```
TypeError                                 Traceback (most recent call last)
<ipython-input-8-aace3fd1d074> in <module>
      2 col = intake.open_esm_datastore(url)
      3 cat = col.search(variable_id='o2', source_id='CanESM5', experiment_id='historical')
----> 4 dd = cat.to_dataset_dict(zarr_kwargs={'consolidated':True}, aggregate=False)

TypeError: to_dataset_dict() got an unexpected keyword argument 'aggregate'
```
It seems as if that option was deprecated, but not removed from the docstring. Is there another way to recover the old behavior?

tests/test_source.py::test_esm_group_invalid_df[x0] tests/test_source.py::test_esm_group_invalid_df[x1] tests/test_source.py::test_esm_group_invalid_df[x2] tests/test_source.py::test_esm_group_invalid_df[None] tests/test_source.py::test_esm_single_source_invalid_row[row0] tests/test_source.py::test_esm_single_source_invalid_row[row1] tests/test_source.py::test_esm_single_source_invalid_row[row2] tests/test_source.py::test_esm_single_source_invalid_row[None]