Our I.lvnii; Resources — Plants 



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Bivophytes (mosses, liverworts, and horn- 

 worts) are small green plants that reproduce 

 by means of spores (or vegetatively) instead of 

 seeds. Most are only a few centimeters high, 

 although some mosses attain a half meter (20 in) 

 or more. Although often small and inconspicu- 

 ous, bryophytes are remarkably resilient and suc- 

 cessful. They are sensitive indicators of air and 

 water pollution, and play important roles in the 

 cycling of water and nutrients and in relation- 

 ships with many other plants and animals. 

 Information about bryophytes and their ecology 

 is essential to develop comprehensive conserva- 

 tion and management policies and to restore 

 degraded ecosystems. 



There are three main groups of bryophytes: 

 mosses (Musci); liverworts, also known as hepat- 

 ics (Hepaticae); and homworts (Anthocerotae). 

 Bryophytes rank second (after the flowering 

 plants) among major groups of green land plants, 

 with an estimated 15.000-18,000 species world- 

 wide. In North America north of Mexico, there 

 are 1,320 species of mosses in 312 genera 

 (Anderson et al. 1990), and 525 species of hepat- 

 ics and homworts in 119 genera (Stotler and 

 Crandall-Stotler 1977), or somewhat more than 

 10% of the world's bryophyte species. 



Mosses are most abundant and conspicuous in 

 moist habitats, but are also found in grasslands 

 and deserts, where they endure prolonged dry 

 periods. Hepatics also include some arid-adapted 

 species, but most are plants of humid environ- 

 ments. In mosses and leafy hepatics. the conspic- 

 uous plant body is leafy; in some liverworts and 

 all homworts, the plant is a flattened, ribbon-like 

 "thallus" that lies flat on the ground. Bryophytes 

 have no roots but are anchored by slender threads 

 called rhizoids, which also play a role in the 

 absorption of water and mineral nutrients. 



Bryophytes have successfully exploited many 

 environments, perhaps partly because they are 

 rarely in direct competition with higher plants 

 (Anderson 1980). For such small organisms, the 

 climate near the ground (microclimate) is often 

 very different from conditions recorded by stan- 

 dard meteorological methods, and shifts in tem- 

 perature and humidity are often extreme. A 

 remarkable adaptation of bryophytes is their abil- 

 ity to remain alive for long periods without water, 

 even under high temperatures, then resume pho- 

 tosynthesis within seconds after being moistened 

 by rain or dew. 



Ecological Roles 



Most bryophytes appear to absorb water and 

 mineral nutrients directly into leaves and stems, a 

 fact that makes them extremely vulnerable to air- 

 borne pollutants in solution (see references in 

 Longton 1980). Where abundant, bryophytes 



may constitute an important sink for moisture 

 and nutrients. Mosses are reliable indicators of 

 soil conditions because they tend to accumulate 

 chemical elements somewhat indiscriminately. 

 The analysis of concentrations of pollutants in 

 older bryophyte specimens could be used to doc- 

 ument increases in pollution levels over time. 



Bryophytes are also closely associated with 

 organisms as diverse as protozoa, rotifers (micro- 

 scopic aquatic animals), nematodes, earthworms, 

 mollusks, insects, and spiders (Gerson 1982), as 

 well as plants and fungi. Direct interactions of 

 bryophytes include providing food, shelter, and 

 nesting materials for small mammals and inverte- 

 brates; indirectly, they serve as a matrix for a 

 variety of interactions between organisms. 



Bryophytes occur in all types of environ- 

 ments, except salt water. They occur on both 

 shaded and exposed soil and rocks, the bark of 

 living trees, and on decaying logs and litter in 

 humid forests (evergreen and deciduous). Many 

 are subaquatic in swamps, bogs, and fens, and 

 some grow submerged or emergent in streams. 

 There are no marine bryophytes, but a few grow 

 on coastline rocks and can tolerate exposure to 

 salt spray. 



Bryophytes 



by 



Gary L. Smith Merrill 



The Field Museum, Chicago 



In the moss-caipeted rainforests of the Pacific 

 Northwest, bryophytes make up a significant pro- 

 portion of the biomass. Peat moss {Sphciiinum) is 

 a dominant organism in northem peatland com- 

 munities and is of some economic importance in 

 horticulture and as an energy source. Bryophytes 

 of arid grasslands and deserts are few, but there 

 are mosses that appear adapted to prairies and to 

 the periodic intense disturbance of grazing and 

 tire (Merrill 1991). 



Floristics and Distribution 



Basic information on the distribution of 

 bryophytes is available for at least the northeast- 

 em United States, eastern Canada, and the Pacific 



Tlie newly discovered moss genus 

 ,ind species. Ozohryum ogalalense, 

 IS known only from four localities 

 Ml northwest Kansas and adjacent 

 Nebraska (Merrill 1992). The 

 species fomis soft, compact cush- 

 ions on exposed lime-rich outcrops 

 in native prairie pastures. The out- 

 crops are porous and charged with 

 moisture, making them a magnet 

 for several species of bryophytes in 

 an otherwise hostile environment. 

 Ozobryiim underscores the fact that 

 discoveries can still be made in 

 areas of the country where 

 bryophytes are poorly known. 



