Pressed specimens of Arceuthobium are easily broken or fragmented. The plants invariably fragment if a large host branch is pressed with an attached dwarf mistletoe. Relatively little fragmentation occurs, however, if individual shoots are pressed rather than the entire plant. The basal shoot internodes are sometimes taxonomically important, and thus dwarf mistletoe shoots should be cut from the host branch so that a small portion of the bark remains attached to each shoot. For smaller species such as A. douglasii or A. pusillum, the entire infected host branch can be pressed if it measures less than about 0.5 cm in diameter. Collection of both staminate and pistillate dwarf mistletoe plants is desirable. Also, it is critical to include sufficient host foliage to facilitate its identification.
The collection data on herbarium specimens are usually meager. Information that should be recorded when collecting dwarf mistletoes includes location, date, host (not only that of the specific collection but other associated infected trees as well), ecological data about the site, and shoot characters such as habit, size, sexual dimorphism, and original color. Also, the presence or absence of witches’ brooms should be recorded. If more than one host species is involved, their relative susceptibility should be noted.
Mounted herbarium specimens were better preserved when we used a heavy grade herbarium paper and a heavy coat of adhesive applied to the back of each specimen before the plants became totally dry. Another satisfactory method is to use a cotton-backed envelope or Riker Mount. A modification of the latter is to place the dried specimen directly on Tomac, and file it in a large envelope with a transparent window so it can be observed with little handling.
Ag Handbook 709 home page