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Trees of Wisconsin

Picea mariana (Mill.) Britton, Sterns and Poggenb.
black spruce
Family: Pinaceae

Black Tree Witch's Broom Black Branch Black Twig Black Cones
tree witch's broom branch pubescent twig cones

Picea mariana can be recognized as a spruce by needles squarish in cross-section and attached to woody projections (sterigmata) of the twig. It can be distinguished from the other spruces in Wisconsin by the presence of short pubescence of the young twigs, and by the short cones that generally are less that 3 cm long. The other spruces have glabrous twigs and longer cones. It also tends to have the shortest leaves, usually 6-10 mm, while the leaves of other spruces are longer than 10 mm and often longer than 15 mm. The situation is not so clear in Door County, near Lake Michigan where some spruces, presumably P. glauca, have glabrous twigs but needles as short as P. mariana. Cones, if present, will distinguish these plants.

Picea mariana is the host for Arceuthobium pusillum, Wisconsin's only species of mistletoe. A. pusillum is parasitic on the branches of P. mariana (and perhaps rarely P. glauca), and causes the profuse growth of branches known as a "witch's broom".

The range of Picea mariana is similar to that of P. glauca, but P. mariana prefers a much wetter habitat in Wisconsin. It is most often found in old bogs and in northern coniferous forests, often with Larix laricina. Proceeding north into Canada, P. mariana becomes increasingly successful in more upland settings and is usually the last surviving tree as the forest grades into the treeless communities of northern Canada.

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