July 21, 2017

A Particular Parasite

Arceuthobium pusillum

Arceuthobium pusillum - Photos courtesy of Glen Mittelhauser/Maine Natural History Observatory

Arceuthobium pusillum has a way of getting to a tree. That is if you are a spruce, larch or pine in Maine. It’s not particularly showy or useful, even if its near relative is part of a revered Christmas tradition: kissing under the mistletoe. A. pusillum is dwarf mistletoe, kind of the wallflower cousin with its short yellow-green stems and and leaves reduced to brown scales. In fact, dwarf mistletoe has another effect on trees. On infected spruce, it causes a hormone imbalance that causes a proliferation of twigs called witches brooms, according to the Minnesota Department of Natural Resources. And how does dwarf mistletoe spread? Thank the birds, who either drop them you-know-how or by wiping the sticky seeds off their beaks and onto branches where the sticky seeds stick and eventually take hold. Dwarf mistletoe has another curious characteristic: It is one of the rare plants that blossoms in winter.

Wild Wednesday is a collaboration of Garden Maine and Glen Mittelhauser of the nonprofit Maine Natural History Observatory, www.mainenaturalhistory.org.