Coefficient of Conservatism:
Coefficient of Wetness:
R. W. Smith
A tiny parasite, the shoots seldom over 1 cm long, on the branches of spruce. The commonest host is Black Spruce (Picea mariana) and hence it is usually found in bogs, where it is rather frequent in Michigan, often locally abundant. However, as also in Door Co., Wisconsin and the Lake Huron shores in Ontario, it also parasitizes White Spruce (P. glauca) in thickets and at borders of forests, especially on dunes, near the Great Lakes shore (Drummond Island, Bois Blanc Island, Beaver Island, and Wilderness State Park in Emmet Co.). Elsewhere in the Great Lakes region, it has been found rarely on Jack Pine and Red Pine (Pinus banksiana and P. resinosa) and Tamarack (Larix laricina). Thus far, the southernmost stands of spruce in Michigan seem to be free of mistletoe, which occurs only in the northern part of the state, whence it ranges northward to Hudson Bay (but not as far north as spruce).
Our dwarf mistletoe is one of the first plants to bloom, in late March to May, often at or a little before Red Maple is in flower. The sexes are separate, and pollination is primarily by insects. The minute perianth of the pistillate flower is 2-toothed; the staminate flower is only slightly more noticeable, with 3 (–4) small lobes, each bearing a yellow anther. The 1-seeded berry, ca. 3 mm long, ripens in the fall and the seed is expelled by rapid contraction of the fruit, traveling perhaps as much as 6 to 12 m or more. Wind and even birds or squirrels, aided by a viscous coating on the seed, may play minor roles in dispersal. Germination of the seed and penetration of the host by the rapidly growing fungus-like absorptive tissues of the plant ordinarily occur the following spring. Plants do not flower until the fourth season and consequently fertile material will not be found on younger branches of the host.
The most conspicuous effect on the host is to produce the deformity known as a “witch's broom.” The dwarf mistletoes are the only flowering plants that induce this unusual growth on the part of other plants, but since many parasitic fungi cause witch’s brooms, the presence of such an aberration of growth is no guarantee that mistletoe is present. Anyone looking for the parasite, however, should watch for these deformities of spruce as a handy indicator. In old, well established infections, some of the host trees may already be dead, their skeletons starkly revealing the witch’s brooms. Fire was formerly a natural means of control.