Salix nigra – Black Willow

Persistent stipules are a distinguishing feature.

Uncommon in Ottawa and frequently confused with the more abundant and widespread  non-native Hybrid Crack Willow (S. x fragilis), Black Willows become medium to large trees, often with broad, open crowns.  The bark is deeply furrowed, dark grey/brown tending to plated in old trees.  Leaves are long, lanceolate, finely serrated, broad at the base, tapering to a long point, dark green above, duller green below.  Persistent stipules on second year twigs are a distinguishing feature.

Black Willow growing as a shrub on the Petrie Island shoreline.

One of the few places where Black Willow is found in abundance is Petrie Island.  There it can grow to full tree size, usually set back from the shoreline, where otherwise it is coppiced regularly to shrub form on the ice-scoured Ottawa River beaches. Large, mature specimens grow on the north beach towards the west end beyond the trail system. Black Willows can also be found at Andrew Haydon Park.

 

Selected photographs with location coordinates in iNaturalist:
https://www.inaturalist.org/observations/2897273 – good photos of leaves at Constance Bay.
https://www.inaturalist.org/observations/8148207 – bark and male flowers at Petrie Island in June.
https://www.inaturalist.org/observations/2693150 – persistent stipules at Andrew Haydon Park.
https://www.inaturalist.org/observations/33536463 – upright tree form at Petrie Island.
https://www.inaturalist.org/observations/4847103 – female flowers at Petrie Island in June.
https://www.inaturalist.org/observations/51651425 – small tree at Alvin Runnalls Forest.

Distinguishing Black Willow, Hybrid Crack Willow, and White Willow

Hybrid Crack Willows at the Kanata Beaver Pond.

Because these willows easily hybridize with one another, it can sometimes be difficult to determine exactly what the tree in front of you is.  However, there are means to distinguish our native Black Willow from Hybrid Crack and White.

First let’s address the latest nomenclature, which comes from iNaturalist.  Crack Willows in Ottawa are generally considered to be hybrids of Crack Willow (S. euxina, formerly S. fragilis) and White Willow (S. alba) called Hybrid Crack Willow  (S. x fragilis).  Without genetic testing, it’s probably safest to make this assumption as the two hybridize freely into variable, intermediate forms.  All are non-native to North America.

Black Willow vs. Hybrid Crack Willow – Both have long, lanceolate, finely serrated leaves and similar furrowed bark.  Distinguishing characteristics are:
  1. Black Willow has persistent stipules on second year wood.
  2. Hybrid Crack Willow is true to its fragilis name:  take a young, but woody twig and bend it.  If it easily breaks, it’s Hybrid Crack.
  3. Black Willow often appears darker green than Hybrid Crack Willow (possibly due to White Willow’s contribution to its parentage).  The underside of a Black Willow leaf, although lighter and duller than its top side, is usually darker than the underside of Hybrid Crack Willow leaves, which can be, although not always, glaucous (blueish-white).
Persistent stipules and dark underside of Black Willow (photo by O. Clarkin).
Hybrid Crack Willow leaves with glaucous underside.

 

 

 

 

 

 

Hybrid Crack Willows can grow to be very large, multi-stemmed trees with spreading crowns.  They are common on the banks of our rivers, streams, and ponds, often with limbs broken off as they age.  Black Willow is a medium to large tree and uncommon in our area.

The silvery appearance of White Willow (photo by O. Clarkin).

White Willow (S. alba) – This non-native willow has a distinctive, silvery, light colour reminiscent of Russian Olive (Elaeagnus angustifolia).  It can hybridize with Black Willow, Shining Willow (S. lucida), and Sandbar Willow (S. interior).  White Willow twigs are flexible; use the woody twig break test described above to determine if the tree is a hybrid.

 

 

https://www.inaturalist.org/observations/9107010 – multiple photos taken in Ottawa’s eastern greenbelt.
https://www.inaturalist.org/observations/8161375 – Beechwood Cemetery.
https://www.inaturalist.org/observations/4833782 – in Barrhaven with flowers (late May).