Andreaea is one of two moss genera belonging to the class of mosses known as Andreaeidae and the family Andreacea. Andreaeidae, referred to as the granite mosses, are commonly found on granite rock faces in mountainous and arctic regions. Andreaea, a genus comprised of about 100 species, is the single representative of Andreaeidae found in North America with the exception of Andreaeobryum, which has been found in Canada and Alaska. Andreaea rupestris Hedw. and Andreaea rothii Web. & Mohr are the two most commonly identified representative species found in North America. The range of A. rupestris Hedw. in North America is Canada and Alaska south to North Carolina, Colorado and Oregon. A. rothii is less widespread commonly occurring in eastern North America. A. rothii has been identified in Jackson and Hocking county. A. rupestris has been found as close as the Upper Peninsula, Michigan.
Macroscopically, the gametophyte of Andreaea is recognized by its unique dark-green to red-brown or black appearance which often forms cushions or tufts on exposed rocks, ledges, or cliffs. These tufts have slender branching stems lacking a central axis. Leaf shape in the common North American species tend to vary. A. rupestris forms fiddle shaped leaves lacking a costa. A. rothii tends to taper into more narrow leaves divided by a costa. Leaves of both species are mostly concave and oblong-ovate standing erect at the base. Leaf margins are usually entire and the gametophyte’s tissue is comprised of uniform, thickened, pappiliose and porose cells containing oil globules.
The sporophyte in Andreaea usually consists of a foot and capsule and lacks a seta. The capsule extends from the gametopyte on an elongate pseudopodium. The capsule is easily recognized by its paper-lantern-like dehiscence. Lacking peristome teeth, the capsule splits along four longitudinal slits as a result cell weakness. The longitudinal valves are responsive to humidity, which allows the spores to be carried away when the air is dry and conditions are optimal, closing when the air becomes moist. This dehiscence type is a unique characteristic and occurs exclusively among the granite mosses. When present, the calyptra is small and mitrate. Spores within the capsule often undergo cell division before being emitted. Similar to spore discharge in liverworts, this adapted mechanism ensures survival in harsh conditions.
Crum, Howard, Mosses of the Great Lakes Forest third ed., University of Michigan: Ann Arbor, 1983, pg. 52-53.
Darlington, The Mosses of Michigan, Cranbrook Institute of Science: Bloomfield Hills, 1964, pg. 33.
Raven, Evert, & Eichhorn, Biology of Plants, sixth ed., W.H. Freeman and Company: New York, 1999, pg. 412-416.
Richardson, The Biology of Mosses, Blackwell Scientific Publications: New York, 1981, pg.2.
Written by Jeremy McKinney