Arceuthobium

The genus Arceuthobium, commonly called dwarf mistletoes, is a genus of 42 species of parasitic plants that parasitize members of Pinaceae and Cupressaceae in North America, Central America, Asia, Europe, and Africa. Of the 42 species that have been recognized, 39 and 21 of these are endemic to North America and the United States, respectively. They all have very reduced shoots and leaves (mostly reduced to scales) with the bulk of the plant living under the host's bark. Recently the number of species within the genus has been reduced to 26 as a result of more detailed genetic analysis.

==Description== thumb|Female plant of A. vaginatum susbp. cryptopodum on Ponderosa pine They are dioecious, individual plants being either male or female. The fruit is unusual in that it builds up hydrostatic pressure internally when ripe and shoots the single sticky seed up to speeds nearly , an example of rapid plant movement. The lodgepole pine dwarf mistletoe, Arceuthobium americanum, has been found to explosively-disperse its seeds through thermogenesis. Dwarf mistletoe seeds are enveloped in a hygroscopic, glue-like substance called viscin. Many fail to land on a suitable host's shoot, but some succeed, and in this way they are spread through the forests as a pest front. The spread of dwarf mistletoes in forest stands is greatest from the overstory to the understory, owing to gravity. Advantageous stand conditions for the spread of the parasite include an uneven-aged stand structure with severely infected hosts in dominant and codominant crown classes, species composition dominated by the primary host, and tree densities between 175 and 500 trees/ha.