Michigan’s Mistletoe

Arceuthobium pusillum

Dwarf Mistletoe witch’s brooms 

Dwarf Mistletoe (Arceuthobium pusillum) is a parasitic flowering plant found on Black Spruce (Picea mariana) and rarely on other evergreens. It is related to southern Christmas Mistletoe (Phoradendron leucarpum). I learned about Dwarf Mistletoe from Billington’s Shrubs of Michigan when I was a boy. He writes, “To include such a little, inconspicuous plant among the shrubs may be stretching things too far. But it is a shrub, and to discover it may provide the discoverer with a greater thrill than locating many of the larger and more conspicuous plants.” I have looked for this species for decades, never being certain that I found it. It often forms distorted branches termed “witch’s brooms.” Fungi and insects also cause these growths. I looked at the witch’s brooms in this colony before and I was never sure what the cause of their abnormal growth was. When I saw the flowers for the first time last weekend, I knew exactly what they were. I have never walked into Diane’s Bog this early in the growing season.

Arceuthobium pusillum

Male Dwarf Mistletoe flowers

Dwarf Mistletoe is one of our first species to flower. It flowers at the same time as Red Maple (Acer rubrum). I found 16 Black Spruce hosts. Male and female Mistletoe grew on separate hosts. The flowers are 10mm (3/8 inch) high but each host had many blooms. The species is insect pollinated; however, I observed no pollinators at work. Mistletoe does damage or kill host trees.

Arceuthobium pusillum

Female Dwarf Mistletoe flowers

Billington was right, it was thrilling. I seldom find native plant species that I have not seem before. My pulse quickened. I stood and stared at the plant for several minutes, forgetting my cold feet. My sense of wonder renewed. I found the male (staminate) plants first and then looked for the more inconspicuous female (pistillate) plants. I returned an hour later and the sunlight was reaching the plants. I spent several hours just photographing and studying the plants. What a memorable day. You never know what you will find when you go out into nature and look.

May 7, 2016
Copyright 2016 by Donald Drife

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Michigan’s Spruces (Picea)

Spruces have needles less than 20mm (3/4 inch) long with square cross-sections. They never occur in bunches, just one needle per node. They can be confused with Balsam Fir (Abies balsamea) but Firs have needles with flattened cross-sections. If you can roll a needle in your fingertips then it is a spruce.

Balsam Fir and Spruce Needles and Branchlets

Balsam Fir and Spruce Needles and Branchlets

Michigan has two native spruces, Black Spruce (Picea mariana) and White Spruce (P. glauca). Norway Spruce (P. abies) is now naturalized into the state.

Picea mariana branchlets

Black Spruce Branchlets

Picea mariana pegs and cones

Black Spruce pegs and cones

Black Spruce has needles shorter than 16mm (5/8 inch) and densely pubescent, meaning furry, first year branchlets. The needle bases, which sit on a peg-like projection, are difficult to see. These peg-like projections stick out at 90 degrees to the twig. If cones are present, they are about as wide as they are long. In southern Michigan, Black Spruce grows only in cool bogs. North of Bay City, it will also grow in upland forests and interdunal swales. Even in the north, it prefers a damp habitat and often occurs with Tamarack (Larix laricina) and White Cedar (Thuja occidentalis). The common name refers to the dark needles this tree normally has.

Picea glauca needles and cone

White Spruce needles and cone

White Spruce has needles that are normally longer than 16mm (5/8 inch) and hairless first year branchlets. The needle bases are easily seen. The peg-like projections  point forward at approximately 60 degrees from the twig. Cones are two to three times longer than wide. The tree’s native range is north of West Branch. It grows in similar habitats as Black Spruce but will also thrive in drier locations. The common name refers to the waxy layer on the young needles.

Picea abies needles and cone

Norway Spruce needles and cone

The native range of Norway Spruce is central and northern Europe. It is escaping throughout Michigan. The branchlets droop and its cones are large, approximately 130mm (5 inch) long. Norway Spruce is commonly planted and beginning to escape into natural areas. Its needles are stiff and have rows of minute openings properly called stomata.

Picea abies stomata

Norway Spruce stomata

Copyright 2014 by Donald Drife

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