Eastern dwarf mistletoe

Appearance

Eastern dwarf mistletoe is a hemiparasitic plant which grows inside the stems of a host plant. Once a seed lands on a branch it will germinate and grow a haustorium which penetrates past the cambium layer and into the host's xylem and phloem tissues; from those tissues it gathers nutrients needed for its own growth and reproduction. Until the mistletoe grows aerial stems it will be completely reliant on the host for all nutrients and energy; even after it grows aerial stems it will still not produce enough energy to support itself and will still be still reliant on the host.

After 2–12 years from the start of the infection the mistletoe will grow aerial stems outside of the stem it inhabits, these stems are often inconspicuous at 0.5–3 centimetres . The stems may pale yellow green and the male stems may be red or red-brown. Dwarf mistletoe is dioecious,with distinct male and female plants: the male flowers are 2mm across and mostly trimerous but may be 2–4-merous. The mature fruits are green, 1.5-3mm sized berry. Seeds ripen in the autumn and the fruits forcefully eject seeds which are coated in a sticky substance that allows them to adhere to whatever they touch. After rain, the sticky seed will slide down a needle that it has landed on onto a stem where it will then germinate and enter into the host. The seeds may spread long distances via animals.

Naming

Arceuthobium pusillum Peck
Razoumofskya pusilla (Peck) Kuntze

Status

''A. pusillum'' is listed as endangered in Connecticut, New Jersey, and Rhode Island as well as threatened in Pennsylvania.

Behavior

Parasitic mainly on black spruce but sometimes on tamarack, white spruce, jack pine, and red pine.

Habitat

On black spruce branches (although it can infect other conifers). This species is most often seen in boggy habitats where black spruce is the predominant tree species.

Reproduction

Sexes are on separate plants and pollination is by insects. Flowering time is between March to May. The seeds are ejected from ripe fruit at a high speed and can travel as far as 15 meters. A sticky mucilage allows the seeds to adhere to any branches they land on. Under good conditions, the seed will germinate and send roots into the tree's living tissue. The seeds can also be transported on the feathers and fur of birds and small arboreal mammals.

Food

Dwarf mistletoe has very restricted photosynthetic ability and so receives almost all of its carbohydrates as well as other nutrients and water from the host tree.

Predators

Dwarf mistletoe is host to a fungus,

Caliciopsis arceuthobii (Peck) Barr (ex Wallrothiella arceuthobii (Peck) Saccardo) was first described infecting
Arceuthobium pusillum Peck in 1873 by Peck (in Weir 1915) as Sphaeria arceuthobii Peck. This pathogen displays extreme host specificity, infecting only the pistillate flowers of the spring-flowering dwarf mistletoes A. pusillum, Arceuthobium americanum Nuttal ex Engelmann in Gray, Arceuthobium douglasii Engelmann, and Arceuthobium vaginatum (Willdenow) Presl in Berchtold, subsp. cryptopodum (Engelmann) Hawksworth & Weins (Kuijt 1969; Hawksworth et al. 1977).