diff --git a/arrow/arrow.py b/arrow/arrow.py
index 8d329efd..19132f98 100644
--- a/arrow/arrow.py
+++ b/arrow/arrow.py
@@ -303,7 +303,9 @@ def utcfromtimestamp(cls, timestamp: Union[int, float, str]) -> "Arrow":
         )
 
     @classmethod
-    def fromdatetime(cls, dt: dt_datetime, tzinfo: Optional[TZ_EXPR] = None) -> "Arrow":
+    def fromdatetime(
+        cls, dt: Union["Arrow", dt_datetime], tzinfo: Optional[TZ_EXPR] = None
+    ) -> "Arrow":
         """Constructs an :class:`Arrow <arrow.arrow.Arrow>` object from a ``datetime`` and
         optional replacement timezone.
 
@@ -318,6 +320,10 @@ def fromdatetime(cls, dt: dt_datetime, tzinfo: Optional[TZ_EXPR] = None) -> "Arr
             >>> arrow.Arrow.fromdatetime(dt)
             <Arrow [2021-04-07T13:48:00-07:00]>
 
+        **NOTE**:
+            Although you can pass a :class:`Arrow <arrow.arrow.Arrow>`, doing so is not recommended
+            except for some cases where it simplifies handling both.
+
         """
 
         if tzinfo is None:
@@ -635,8 +641,8 @@ def ceil(self, frame: _T_FRAMES) -> "Arrow":
     def span_range(
         cls,
         frame: _T_FRAMES,
-        start: dt_datetime,
-        end: dt_datetime,
+        start: Union["Arrow", dt_datetime],
+        end: Union["Arrow", dt_datetime],
         tz: Optional[TZ_EXPR] = None,
         limit: Optional[int] = None,
         bounds: _BOUNDS = "[)",
@@ -646,8 +652,8 @@ def span_range(
         representing a series of timespans between two inputs.
 
         :param frame: The timeframe.  Can be any ``datetime`` property (day, hour, minute...).
-        :param start: A datetime expression, the start of the range.
-        :param end: (optional) A datetime expression, the end of the range.
+        :param start: A datetime or :class:`Arrow <arrow.arrow.Arrow>` expression, the start of the range.
+        :param end: (optional) A datetime or :class:`Arrow <arrow.arrow.Arrow>` expression, the end of the range.
         :param tz: (optional) A :ref:`timezone expression <tz-expr>`.  Defaults to
             ``start``'s timezone, or UTC if ``start`` is naive.
         :param limit: (optional) A maximum number of tuples to return.