Fraxinus quadrangulata

Blue ash or Ontario blue ash is in the olive or Oleaceae family and is native to the U.S. to an area south of Lake Michigan including parts of Michigan, Oklahoma, Kentucky and Tennessee. Pioneers used to extract blue dye from its inner bark.

As of 2014, blue ash appears to be least threatened in comparison to other North American ash by the infestation of the emerald ash borer, with over 60% survival of trees in attacked areas.

• Leaves are 20–38 cm long, with 5–11 (most often 7) leaflets, the leaflets 7–13 cm long and 2.5–5 cm broad, with a coarsely serrated margin and short but distinct petioles.
• Flowers are small and purplish, produced in the early spring before the leaves appear.
• Fruit is a samara 2.5–5 cm long and 6–12 mm broad, including the wing.
• Twigs typically have four corky ridges, a distinctive feature giving them a square appearance (in cross-section), thus the name 'quadrangulata'(four-angled). Winter buds are reddish-brown.