Pennsylvania Biological Survey

The Bryophyte and Lichen Technical Committee of the Pennsylvania Biological Survey had its inception on April 18, 1986, when persons interested in forming the present Pennsylvania Biological Survey met in Harrisburg, Pennsylvania. The first meeting of the Technical Committee was held March 12, 1987, in State College, Pennsylvania. The Bryophyte and Lichen Technical Committee shares the overall goals of the Pennsylvania Biological Survey, with a specific focus on gaining a better understanding of the bryophyte and lichen flora of the state. The Technical Committee is able to advise the Pennsylvania Bureau of Forestry regarding the status of bryophytes and lichens under the Wild Resources Conservation Act and members are conducting research on the distribution and taxonomy of the State’s bryophytes and lichens.

BRYOPHYTES AND LICHENS: REVIEW OF STATUS IN PENNSYLVANIA

G. Christine Manville
Academy of Natural Sciences, Philadelphia

Harold J. Webster
The Pennsylvania State University at Dubois

Jack R. Stabley, Jr.

INTRODUCTION

Although bryophytes and lichens are often grouped together because of common habitat, the organisms differ markedly in structure. Bryophytes (mosses, liverworts, and hornworts) are autotrophic plants; mosses are generally radially symmetric, with sporophytes of variable and complex differentiation. Liverworts are bilaterally symmetric, and may be strap-shaped, or "thalloid", a growth form also seen in hornworts. Hornworts differ microscopically from thalloid liverworts in the presence of but a single chloroplast in each cell in most taxa, each of which contains a dark granule or pyrenoid. Liverwort sporophytes are spherical and of determinate growth; hornwort sporophytes are linear and of indeterminate basipetal growth.

Lichens are often studied with fungi, as "lichenized fungi", because the more obvious symbiont is fungal, in mutualistic association with algae. In temperate regions, the fungal component (or mycobiont) is of ascomycetic structure that can be cultured, much as other fungi. The algal photobiont consists of a layer of green algae such as Trebouxia, or cyanobacteria (blue-green algae) such as Nostoc or Stigonema, which can exist separately in nature. Bacterial nodules may be a part of the consociation. There are three basic growth forms of lichens: foliose, fruticose, and crustose. Foliose lichens look much like large thalloid liverworts, with immersed or sessile ascocarps. Fruticose lichens bear the ascocarps on extended branches of the thallus, or on stalks or podetia on which ascocarps are raised above the thallus. Crustose forms, with thalli adherent to the substrate and with sessile ascocarps, colonize and persist on rocks and trees, often in extensive patches.

Bryophytes and lichens, together with fungi and algae, are often classed as "lower" plants, since they produce neither showy inflorescences nor large trees. They tend to blend in with the scenery, literally, and are not as frequently noticed as the flowering plants or trees that comprise a forest canopy. Like their "hidden" gametes -- hence the name "cryptogams" -- their function in ecosystems is often hidden. Yet these plants may serve as pioneers on sites that have accumulated heavy metals (the mosses Scopilophila cataractae, Mielichhoferia mielichhoferi, for example), and on bare soil of roadsides (the lichen Baeomyces roseus, and mosses Ceratodon purpureus, Polytrichum spp. or "hair cap mosses", and Bryum spp.). The role of bryophytes and lichens in primary succession leads to soil formation through accumulation of organic materials; this prepares whole banks or rocky outcrops for secondary succession of herbs, shrubs, and trees. Though "hidden", this pioneering -- even opportunistic -- habit of some lichens and mosses plays a significant role in primary and secondary succession, particularly on rocks and rock faces. Crustose lichens and the moss genus Grimmia are the first colonizers of rock, often followed by Cladonia and Polytrichum species, and then by annual and perennial plants (Smith 1966). In xerarch, and occasionally mesarch succession, lichens are an integral part of primary succession; in hydrarch succession, aquatic mosses, e.g., Sphagnum, Drepanocladus, Fissidens, and other aquatic plants provide the initial and intermediary successional phases (Spurr 1964).

Bryophytes, particularly the "feather mosses," e.g., Hylocomium splendens, Thuidium delicatulum, and lichens such as the "reindeer mosses" (Cladina spp.), may also serve as seed beds for native forest trees and wild flowers. Rarer native plants, such as orchids, often grow in mats of bryophytes, particularly in peat mosses (Sphagnum spp.).

In associations with animals, lichens may be a component of the food chain for invertebrates (Gerson and Seaward 1977, Seaward 1988). Mosses, particularly the genus Sphagnum, and other turf-forming moss species, provide habitat for a variety of invertebrates, from nematodes to arthropods, some of which may use these plants as a food source (Clymo and Hayward 1982, Schofield 1985). If sufficiently abundant, as in northern boreal habitats (McAndrews and Manville 1987), lichens may provide extensive forage for deer (Odocoileus virginianus), elk (Cervus elaphus), and other grazing animals. In Pennsylvania, the assertion that lichens may provide forage for vertebrate populations (Richardson and Young 1977) has been verified by observations of selective browsing of macrolichens by white-tailed deer and elk (M. Benner, pers. comm. to R.J. Hill). The less common northern parula warbler (Parula americana), a breeding bird within Pennsylvania, is known to use ephiphytic lichens, particularly the genus Usnea, which may occur in its habitat in old growth forests along rivers (Schwalbe 1992).

A few mosses, notably of the genera Sphagnum and Polytrichum, have long had practical and occasional economic importance; Sphagnum peat has been used as fuel, and the dried moss as insulation because of the air spaces in the leaves and stems, as natural absorbents (sphagnos in Greek means "sponge"), and as an acidifying agent because of cation exchange. Polytrichum was variously used in roping, and as boat caulking, in woven mats, and as mattress filling in prehistoric cultural remains associated with Romans in Britain (Schofield 1985). Mosses are used in ornamental displays of plants and in gardens. Peat mosses, in particular, are commonly used in horticultural applications.

Although lichens have little prominent economic use today, they have had historic use as emergency rations. At Valley Forge, Pennsylvania, Washington's troops used boiled rock tripes to extract a gelatinous thickening for soup. Lichens are high in caloric content, although slow growth and the presence of irritating acids limits their use as food. In the past, lichens were also used in natural dyes, the extraction of which were closely guarded formulae. However, the introduction of dyes derived from coal tar in the 19th century led to the replacement of lichens as primary dyestuffs. There are two modern commercial uses of lichens: litmus paper (an indicator of acids and bases), and as an aroma stabilizer in expensive perfumes (Hale 1961).

Mosses and hepatics are used in biogeochemical monitoring of heavy metal content within their environment because they serve as efficient absorbers of water- born pollutants, heavy metals, and radio nuclides (Rao 1982). Both bryophytes and lichens are sensitive to airborne effluents surrounding industrial and urban areas and serve as indicators of air quality. Studies of zinc smelting operations at Palmerton, Pennsylvania (Nash 1972, 1988) and industrial areas of western Pennsylvania (Showman and Long 1992) have shown a decline in the numbers of lichen species near such sites. A similar decrease in the number of bryophyte species has been observed elsewhere (Rao 1982). Regrettably, the lichen flora of the state is not well understood. Studies of pollution effects have added to our knowledge of lichens within the Commonwealth. Unfortunately, such studies are an indirect indication of what may have been lost to the flora since the middle of the 19th century.

HISTORY

Bryophytes and lichens in Pennsylvania have been studied since the 1740s, when John Bartram sent specimens from eastern Pennsylvania, New Jersey, and Virginia to Peter Collinson and Hans Sloane in England, as well as to Dillenius, Grovenius, and Linneus (Buck and McLean 1985, Manville 1987). Both bryophytes and lichens were termed "mosses" by Dillenius (1742). Linnaeus did not quite know where to place lichens systematically (Ahmadjian 1995). Mycologists of the 18th century often treated lichens as a single genus. Although the number of genera has multipled substantially, modern lichen systematists follow the concept of "lichen forming, lichenicolous and allied fungi" (Esslinger and Egan 1995).

Work on bryophytes and lichens continued through the efforts of G.H.N. Muhlenberg (1813) and Lewis D. von Schweinitz into the early 19th century, and provided specimens for the description of new taxa. After that time, bryophytes and lichens were studied separately. In the middle of the 19th century, T.P. James (Sayre 1984) and T.C. Porter (Porter 1904) began a survey of bryophytes in Pennsylvania. They were assisted in their work by collectors in other areas: L. Lesquereaux and W.S. Sullivant in western Pennsylvania adjacent to Ohio, A. Simonton and A. Linn in Washington County, J. McMinn in Elk County, F. Wolle, A.P. Garber, and E.A. Rau in Carbon, Northampton, and Lehigh Counties, and J.K. Small in Lancaster County (Small 1892). This combined work was published by J.K. Small of The New York Botanical Garden (Porter 1904), three years after Porter's death. At about the same time of this publication, there was increased interest in bryophytes throughout the state, to which the efforts of others were added: O.E. Jennings in Pittsburgh, W.R. Taylor, A.F.K. Krout, and G.B. Kaiser (1916) in Philadelphia, and W.R. Barbour in Bradford County. Jennings served as editor of The Bryologist, the publication of Sullivant Moss Society (later the American Bryological and Lichenological Society) from 1913 to 1938. From 1915 to 1952, several works were published: O.E. Jennings (1913, 1951), L.M.H. Lanfear's list of western Pennsylvania hepatics (1933 a-c), and G.M. Tees (1933) compiled a list of mosses of the Philadelphia region. These combined studies built upon the work of E.B. Bartram (1921), T. Little (1931; 1932), and H.E. Greenwood (1923). This work was further expanded by S.K. Eastwood's (1936) work on Buxbaumia distribution in western Pennsylvania, and his collections of other bryophytes in western Pennsylvania between 1931 and 1950. There is a significant body of unpublished herbarium records, in addition to S.K. Eastwood's collections in western Pennsylvania. H. Wilkens collected bryophytes from 1925 to 1972 in Berks County. N. Ammons continued work on the bryophyte flora of western Pennsylvania, notably Erie County and southwestern Pennsylvania, along with her work on the hepatics of West Virginia (1940). A.M. Barkman also collected bryophytes in southwestern Pennsylvania between 1940 and 1970.

Moul (1952) incorporated the work of James, Porter, Small, and Tees, and made additional collections in the central and eastern portions of the Commonwealth. H.W. Pretz also collected bryophytes as part of his studies of Lehigh County between 1940 and 1950, as seen in herbarium records. T.S. Githens, a physician who was also an amateur bryologist, published additional lists of mosses from the same area, notably in Sullivan and Monroe Counties (Githens 1957). In 1955, R.A. Pursell began work on the bryophytes of the Commonwealth. He and others (Pursell 1956, 1973, 1975; Williams 1971; Manuel 1975; Allen 1979) have provided many new records in northcentral Pennsylvania. Boardman (1977) published additional records from western Pennsylvania. The work of F.B. Buser provides detailed information on Monroe, Northampton, Pike, and Carbon counties, although much of this has not been published. P. Biebel and his students provided lists of specific sites in Cumberland County (Ainley 1968) and herbarium records for Perry County. Recent work includes that of Bartholomew-Began (1993) for Berks County. Continuing work includes the floristic studies of Allen and Pursell in central Pennsylvania, of Andrus on the Sphagnaceae, and studies of specific restricted habitats such as serpentine barrens, calcareous fens, and seeps for The Nature Conservancy.

Lichens have received far less attention in the Commonwealth than have bryophytes. In the 1890s and early 1900s, J.W. Eckfeldt and E. Tuckerman began studies of lichens that included Pennsylvania. Eckfeldt's collections from Delaware and Philadelphia Counties often lack definitive location data. Specimens from Lancaster County from that era were sent to the Smithsonian Institution. Although O.E. Jennings, A.W. Evans, J.W. Thomson, and others collected lichens, there was no separate checklist until H.N. Mozingo (1948), a student of O.E. Jennings, published a checklist of western Pennsylvania lichens, expanding on the preliminary work of Giardini (1922). W.L. Dix (1943, 1944, 1949) and A.W. Evans' (1947: 1955) studies on the Cladoniaceae and M.E. Hale's (1955; 1965; 1976a, b) studies on the lichen family Parmeliaceae include collections from Pennsylvania. An unpublished checklist compiled by J.K. McGrath (1990 ms.) contains only a portion of the lichens collected from the Commonwealth.

Sites of special interest such as Ohiopyle (Fayette County), Hearts Content (Forest and Clarion Counties), Bear Meadows Natural Area (Centre County), Alan Seeger Natural Area (Huntingdon County), the Poconos and the Delaware Water Gap (Monroe and Pike Counties) have been explored through forays sponsored by the American Bryological and Lichenological Society in 1940 and 1982, and the A.LeRoy Andrews forays in 1977 and 1989 (Chavanngs, 1940; s.a., The Bryologist 1977, p. 558 ; 1982. pp 182, 280). The Bryophyte and Lichen Technical Committee of the Pennsylvania Biological Survey continues to explore state areas such as Nolde State Park (Berks County, 1988), R.B. Winter State Park (Union County, 1989), Bald Eagle State Forest (Snyder County, 1989), Rickett's Glenn State Park (Luzerne County, 1993), and Gifford Pinchot State Park (York County, 1998). Members of the Bryophyte and Lichen Technical Committee of the Pennsylvania Biological Survey have also explored Berks, Bucks, Centre, Clearfield, Clarion, Chester, Delaware, Erie, Lancaster, Sullivan, Washington, and Wayne Counties within the past decade.

WHERE THE ORGANISMS ARE FOUND

Mosses are found in varied habitats. Ubiquitous mosses such as common Bryum and Pohlia species, Ceratodon purpureus, and some Polytrichum species can be found in any open, suitably moist habitats, and are often pioneers on soil, stream banks, rocks, roadsides, and tree bark. Other mosses (Tortula, Grimmia and Bryum species, and crustose lichens) may colonize rocks and rock crevices. Orthotrichum and Anacamptodon species may grow on logs and tree trunks. Some mosses are also known to overgrow wood shingles on roof-tops. Woodlands support a variable bryoflora, dependent in part upon substrate and forest cover. In Pennsylvania, common woodland mosses include Leucobryum, Dicranum, and Thuidium species. Some mosses are aquatic, notably Fontinalis, and some Fissidens species, as well as Amblystegium, Drepanocladus, and the peat mosses of the genus Sphagnum. Although there is some correlation variation between habitats and forest type (Jennings 1951, Moul 1952), quantitative studies are lacking in Pennsylvania.

Liverworts generally grow in consistently moist habitats, generally occupying niches where competition with vascular plants is minimal. Spray zones of waterfalls or wetlands such as bogs, fens, and streams seeps, are often rich in hepatics. Shaded old-growth forests also support liverwort growth, particularly in mesic or even hydric habitats. Thalloid liverworts grow on consistently damp rock faces or in wetlands. Other species may grow in shaded crevices and among mosses in more xeric conditions. Liverworts may colonize moist or submerged rocks (Scapania nemorosa, Porella pinnata), grow under water (Ricciocarpus fluitans), and are found on logs and humic soil in mesic forests (Nowellia curvifolia, Bazzania trilobata). Frullania eboracensis grows on tree bark (Lanfear 1933a). Different forest associations favor a variety of liverwort assemblages (Schuster 1949).

Lichens, particularly crustose forms, appear to be drought tolerant, since the mycobiont retains water, and are prominent on exposed rocks, tree trunks, and bare soil. Epiphytic foliose and fruticose lichens thrive on mature timber stands. Variation between forest associations and the lichen flora has been subjectively observed, though not quantitatively substantiated (Mozingo 1948).

PROMINENT COLLECTIONS AND DATA

The primary repository for Pennsylvania mosses is now at the Missouri Botanical Gardens, which received the collections (including Jennings' and Eastwood's material) of the Carnegie Museum in Pittsburgh in the mid-1980s; they also acquired The Pennsylvania State University Bryophyte Herbarium within the past five years. The Missouri Botanical Garden has also assisted the Academy of Natural Sciences in Philadelphia with curating their collections (including materials from Porter and James). Other major repositories are the Moss Herbarium of the American Bryological and Lichenological Society at Duke University, the Smithsonian Institution, and The New York Botanical Garden (which contains many of Porter's collections, as well as those of E.G. Britton, E.A. Rau, T.S. Githens, A.F.K. Krout, and others). The Farlow Herbarium at Harvard University, SUNY Binghamton, the Herbarium of the University of West Virginia, the Academy of Natural Sciences in Philadelphia, and the Darlington Herbarium (University of West Chester) also house collections from the Commonwealth. The 18th century collections of John Bartram are found in several places: Oxford (Dillenian Herbarium), the San Francisco Library (Sutro Library, a special collection), and the Hans Sloane collection in the British Museum of Natural History, London. Muhlenberg's collections are in the Academy of Natural Sciences in Philadelphia, and some of his collections are also found in Dillenius' Herbarium, and in the Hedwig/Schwaegrichen Herbarium at the Conservatoire et jardin botaniques in Geneva (Species Muscorum Frondosorum, 1801). Some early collections from southeastern Pennsylvania may also be with Durand's collections at Herbier, Museum National d'Histoire Naturelle1 in Paris. Recent collections are found in herbaria at Dickinson, East Stroudsburg and Shippensburg Universities, as well as H.J. Webster's collection at The Pennsylvania State University, Dubois Campus. This last collection now includes 19th and early 20th century moss specimens from Washington and Franklin Counties, as well as specimens collected during the past decades. Materials from The Nature Conservancy studies of calcareous fens are being prepared for distribution.

There are few hepatic collections housed in the Commonwealth. The work of early 19th century collectors, Schweinitz and Muhlenberg, are housed as special collections at the Academy of Natural Sciences. The Carnegie Museum collections are in the Herbarium of the University of Colorado Museum in Boulder, and comprise the bulk of western Pennsylvania materials. Additional collections from Pennsylvania (including duplicates from the Carnegie Museum) are housed at The New York Botanical Garden, the Herbarium of The University of West Virginia at Morgantown, the Evans Herbarium at the Peabody Museum of Yale University, the Hepatic Herbarium of the American Bryological and Lichenological Society in Southern Illinois University, the Buser Herbarium at East Stroudsburg, the Smithsonian Institution, The Missouri Botanical Garden, and the private collection of C.F. Reed. Extensive hepatic collections of R.M. Schuster (including specimens for Pennsylvania) are being transferred to The Field Museum in Chicago.

The lichen collections from the Carnegie Museum are also housed in the Herbarium of the University of Colorado Museum. Other prominent collections are at The New York Botanical Garden, The Smithsonian Institution (including A.W. Evans' Cladonia collections), at Ohio State University in Columbus, the Farlow Herbarium, and at the Academy of Natural Sciences in Philadelphia, which includes collections made by J.W. Eckfeldt (Harshberger 1899) and E. Tuckerman (1847-1856, 1848). Replicates of some of Tuckerman's collections are in the Dillenian Herbarium at Oxford. The lichens from Muhlenberg's collections that were identified by Acharius are probably located in the University Herbarium at Upsalla, Sweden.

DOCUMENTATION

In the late 1980s, at the behest of the Pennsylvania Biological Survey, a group of professional, semi-professional, and amateur bryologists and one amateur lichenologist began to compile the records on bryophytes and lichens within the Commonwealth. The initial work, involving redeterminations of bryophytes, was begun by R.A. Pursell. Over 350 moss species, 160 liverworts, and 351 lichens are reported although these figures are probably low. Vitt and Belland's (1997) analysis of mosses in Alberta calculated that approximately 25% of the mosses could be considered rare; in Pennsylvania, about 30% of lichens and hepatics have been collected from one or two counties. Whether these are indeed rare taxa or whether they are simply overlooked has yet to be substantiated.

photograph courtesy of K. Light
(left to right) Oliver Crichton, Bob Hill, Christine Manville, Bioblitz '99.
Field trips are an important part of the Technical Committees work.

For each of the mosses, hepatics, and lichens, one taxon near the limits of its range has not been reported in the Commonwealth since 1900, and is thus known only from historic records. In the case of the moss Broxyphium norvegicum, reportedly collected by Lesquereaux along Slippery Rock Creek in the mid-1800s, the herbarium voucher is missing. The literature citations (Rau and Hervey 1880, Porter 1904, Jennings 1913, 1951) are tantalizing hints of its occurrence. Several attempts to relocate this moss along Slippery Rock Creek by Jennings, Pursell, and the present authors have been unsuccessful. Dumortiera hirsuta, a large thalloid liverwort, has apparently been extirpated since its discovery in 1899 at Bushkill Gap near Easton, Northampton County and south of Pottstown, Chester County in 1899 and 1900. Coenogonium cf. interplexum (originally determined as C. interpositum) or "net lichen", collected in 1919 on sheltered limestone at Bedford Springs by Jennings (Giardini 1922), has not been seen at the site since its original collection. Other taxa, such as the mosses Campylium stellatum, Tomenthypnum nitens, and Sphagnum warnstorfii are restricted to calcareous wetlands, recently studied by The Nature Conservancy.

There are two probable introductions of species: the moss Fissidens exilis (Steere 1950); and the hepatic Lunularia cruciata, found with greenhouse plants in Lewisburg (Little 1931), Philadelphia, and Pittsburgh (Lanfear 1933b); the senior author has seen L. cruciata along a stream at the Morris Arboretum in Philadelphia. The distribution of a zinc tolerant moss, Scopilophila cataractae, on a superfund site near Palmerton, Pennsylvania is unexplained at present, but might also be an introduced moss (Shaw and Beer 1989).

BARRIERS TO CONSERVATION

Lichens, which are sensitive to aerosol chemicals, have declined within Pennsylvania and other industrial and urban areas in response to increased air-borne pollutants, primarily from acidic sulfate emissions (Nash 1972, 1975, Showman and Long 1992). Bryophytes show a similar decline in species abundance in response to pollutants (Rao 1982, McCune et al. 1997). Habitat loss through development, highway construction, and the diminution of woodland and wetland habitats continues to threaten many plant and animal species. Application of fungicides to farmlands may also kill the lichen's mycobiont. In protected areas, however, such as state parks, state forest lands, game lands, and county parks, bryophyte and lichen growth can be impressive, although distributions are now much dissected compared to 250 years ago.

Forest composition since settlement and industrialization has changed radically through extensive clear-cutting and the demise of 2 major forest trees in the past 80 years, viz., the American chestnut (Castanea dentata) and the American elm (Ulmus americana). Continued loss of habitat through industrial, residential, or recreational development and the "control" of biota selected by gardeners and farmers is a major barrier to conservation of infrequent taxa. Just as habitat loss affects vascular plants, the effects on mosses, hepatics, and lichens may also be high, since the occurrence of "lower plants" is often linked to the succession within wetland communities and old- growth forests. Bryophytes and lichens may be found on particular species of forest trees and not on others (Rose 1992). Bryophytes and lichens that grow on soil and rock may endure through several successional stages, provided the physiography is undisturbed. Within Pennsylvania, this is not always assured. Formerly pristine habitats such as those set aside for natural areas are not immune to the effects of declining diversity (Selva 1994). The effects of forest clearance, agriculture, and industry on the flora are nearly as marked as that of past glaciations to the north. Wetland drainage has resulted in a loss of over half the original wetlands of Pennsylvania, and a concomitant loss of associated bryophytes.

INVENTORY AND MONITORING

Despite nearly 250 years of study on the bryophytes and lichens within the Commonwealth, our floristic knowledge is incomplete. There are inventories in varying states of progress compiled both from the literature and the specimens upon which this literature is based. A list of hepatics and hornworts is available in manuscript form from the senior author. These lists are augmented by recent herbarium records of bryophytes and lichens from Pennsylvania. In addition, collaboration with institutions such as The Nature Conservancy and individual ecologists and botanists assists in documenting common and infrequent mosses in selected, infrequent habitats such as calcareous fens, serpentine barrens, and shale barrens. County inventories are also of great importance (Allen and Pursell 1992, ms.).

H.J. Lutz (1930), although he did not include bryophytes or lichens in his study of Hearts Content, recognized their importance as indicators of forest health. O.E. Jennings (1930) proposed several areas of biological interest for western Pennsylvania: Presque Isle, a small swamp near New Castle, Ohiopyle, and Pymatuming Swamp, all of which are rich in infrequently collected bryophytes and vascular plants. Pymatuming has since been flooded to provide a reservoir (Jennings 1951). Cryptogamic inventory and monitoring neither attracts the interest of foresters nor magnanimous donors, in part because the plants blend with the scenery, and are often not considered economically "important". If the plants can be shown to indicate something of value to human welfare, their relative importance in the eyes of an economy-driven society increases.

The concentration of scholars rigorously trained in bryophyte and lichen identification now tends to be at major institutions outside Pennsylvania. Skilled and talented amateurs have long been a part of bryophyte and lichen study, dating from early days in Pennsylvania. For the amateur, studies of these organisms has been a matter of interest and avocation rather than a profession, and the early work was done by farmers, clergy, pharmacists, and physicians who taught courses in natural history in addition to their other duties. There have been exceptions, notably O.E. Jennings at the University of Pittsburgh, R.A. Pursell at The Pennsylvania State University, and F.B. Buser, professors and consummate professionals who have initiated considerable interest among their students, and have added greatly to our understanding of bryophytes through their dedication and scholarship. S. Bartholomew-Began recently began her studies on bryophytes in Pennsylvania, with a focus upon Berks County. Jennings' encouragement was responsible for a survey of the lichen flora of western Pennsylvania (Mozingo 1948).

Incorporating current changes in taxonomy in the database is an important and challenging part of continuing work (Essinger and Egan 1995, Anderson et al. 1990, Stotler and Crandall-Stotler 1977). As bryophytes and lichens are increasingly included in forest ecosystem analysis (Carleton and Maycock 1981, Rose 1992, Selva 1994) and monitoring of sites, information concerning bryophyte and lichen populations will also increase.

GAPS IN INFORMATION

Plant distribution records, particularly for lower plants, are often a function of the distribution of those who are interested in them. Many counties and protected areas have not been adequately surveyed for bryophytes and lichens, although such studies might provide information leading to protection of rare or infrequent taxa. However, we still know exceptionally little, and specific recommendations for proposing any taxa as "rare" are premature. In particular, species of special concern globally have not been consistently identified in Pennsylvania. Thus, we cannot say whether such species (1) have ever occurred in the Commonwealth or (2) if they have, whether they are extant. Even if reported in the literature, flawed or inconsistent identifications impede understanding of the bryophyte and lichen flora.

The foci of research in Pennsylvania have been in the general areas of where those interested in bryophytes and lichens worked, lived, and traveled -- from Bartram's day to the present. Although the Pocono Mountains and the Delaware Water Gap have received considerable attention in the past (Porter 1904, Githens 1957), other areas of northeastern Pennsylvania have not been well explored. The Poconos attracted those working in New England and New York, centers for bryophyte and lichen research. A prominent barrier to understanding the diversity of bryophytes and lichens in the Pennsylvania is the shortage of specialized systematists who study bryophytes and lichens. A related difficulty is that the study of bryophytes and lichens within Pennsylvania remains largely an avocation among botanists, foresters, and ecologists whose time is taken with other studies and projects, or the abiding interest of those who work elsewhere. The professional basis provided by O.E. Jennings, R.A. Pursell, B.H. Allen, F.B. Buser, R.E. Andrus, R.C. Harris, M.E. Hale, I.W. Brodo, and others offer guidance and an impetus for continued study. Their work provides a basis for much of what we know about these organisms and their distribution within Pennsylvania. However, reference specimens may be located in herbaria distant from those actually working within Pennsylvania. This lack of well curated reference material within the Commonwealth is an important obstacle to comparisons of collected material to carefully identified specimens. Rigorous training of those who might otherwise include them in their studies is also lacking. The combination of systematics with floristics, biodiversity, and ecological studies will increase our understanding of any one of these fields. To this end, manuals, floras, and botanical/biotic inventories of lichens and bryophytes would be of great assistance.

Lichen inventories are not available for Pennsylvania except for a single regional article (Mozingo 1948), an unpublished list (McGrath 1990 ms.), and a sulphate gradient survey (Showman and Long 1992). The use of lichens as bioindicators of air quality and the presence of environmental stressors may actually add to our knowledge of lichens within the state. Lichen community surveys similar to that of Huckaby (1993) will include Pennsylvania sites (Kenneth Stolte, Forestry Sciences Laboratory, Research Triangle Park, NC; pers. comm. to R.J. Hill).

A critical gap in our knowledge of lichens in Pennsylvania involves crustose lichens. Weber (1962) gives some insight as to the reasons for this lack of information. The variability of crustose forms, and the great care needed in collection, preparation, and determination often precludes the use of minute fragments often found in older herbarium collections. Weber viewed many of the lichen specimens originally housed at the Carnegie Museum as so fragmentary as to be worthless as voucher specimens because their determination was questionable (Weber 1995, pers. comm.). Amateur lichenologists have thus had few resources upon which to base identifications. Few are trained in mycology, phycology, or chemistry, which modern lichen systematists view as essential tools. A philatelic approach, though marginally useful for bryophyte collections, may be grossly misleading for lichens. Despite recent work by Harris, Brodo, and Wetmore (found in herbarium records), we know little more about the range and distribution of crustose lichens within Pennsylvania than we did when J.W. Eckfeldt collected these taxa 100 years ago. However, the range of variation, global distribution, and taxonomy are much better understood.

Goward (1994) indicated that epiphytic macrolichen colonization occurs in two "pulses" in British Columbia. The first 50-100 years are marked by more "common" and opportunistic species. A later phase which fosters rare taxa (species that occur outside or at the limits of their range) occurs during the second 50-100 years. If this is also true for Pennsylvania, forestry practices and the length of periods between tree harvests will need reevaluation. Forest harvest intervals may not be sufficiently long for the appearance of rare taxa, in part because of large-scale disturbance and changes to secondary and tertiary forest composition. The introduction of forest trees such as Pinus sylvestris (Scots pine) in managed plantations as well as introductions of ornamental trees and weedy exotic herbs have obviously changed the character of Pennsylvania forests and flora, and the habitat available for lichen and bryophyte establishment.

SUMMARY

The numbers of lichens present in Pennsylvania may be underestimated, since the crustose taxa have not been thoroughly studied. Crustose forms comprise nearly 50% of known taxa world-wide; the numbers of lichen taxa throughout the world range from 13,500 to nearly 20,000 (Hawksworth 1991, Nash and Egan 1988, Galloway 1992). The small number (351) reported from Pennsylvania will probably be enhanced by emphasis on crustose taxa. Of the bryophytes, approximately 350 moss taxa, 115 liverworts, and 4 hornworts have been reported from Pennsylvania. An additional 41 liverworts have been reported from New York and New Jersey, and the Appalachians to the south of Pennsylvania, but have not yet been found within Pennsylvania. Here, too, the numbers reported may be low compared to the numbers of taxa world-wide (Shuster 1969-1991). Some taxa are undoubtedly disjunct because the higher, fog- shrouded mountaintop habitats are not frequent. Other species may be overlooked because of their minute size as well as their admixture with more prominent mosses. Jennings (1951) reported 286 species and 33 varieties of mosses from western Pennsylvania. The estimate of 350 moss species throughout the Commonwealth state may also be low. Studies on the effects of industrial and urban airborne sulfate emmissions both within the Commonwealth and elsewhere provides indirect evidence of a more extensive lichen and bryophyte flora.

Despite the gaps in our knowledge about these organisms throughout the Commonwealth, there is considerable information upon which to build. Future work may need to test quantitatively the assertion of Jennings and his students that different lichen and moss associations occur in different types of forests. This approach would refine the quest for less frequent taxa, based upon solid taxonomic, floristic, and ecological studies. Although this approach is a subjective part of all bryophyte and lichen collection, the rigorous identification of all plants within plots in restricted habitats such as calcareous wetlands and seeps, on serpentine and shale barrens, and other infrequent habitats gives additional information, particularly in areas where bryophytes and lichens are a prominent component of the flora. However, an emphasis on restricted habitats may give a biased view of frequency unless the more common habitats -- and the more frequent elements of the bryophyte and lichen flora --are examined as critically.

ACKNOWLEDGMENTS

We acknowledge the considerable assistance of those involved with Pennsylvania Natural Diversity Inventory, primarily Frank Feldbaum, Kathy McKenna, Dan Devlin, and Ed Dix, who have encouraged the work and provided funding for our efforts through grants from the Wild Resources Conservation Fund over the past decade. In addition, we acknowledge the support and critique of Ronald A. Pursell, whose careful work on mosses and hepatics in central Pennsylvania provided both a basis upon which to build and an example of scientific rigor. Frank Buser also provided encouragement and guidance. Bruce Allen of the Missouri Botanical Garden retains an interest in the bryophyte flora of the state. Sharon Bartholomew-Began, Barbara Theirs, and Raymond Stotler have offered comments on hepatic taxonomy. William A. Weber, professor emeritus at the University of Colorado, offered critical comments on the hepatic and lichen flora. I.W. Brodo has assisted by sharing his knowledge concerning lichen distribution, and has reidentified some of the crustose lichens. We are also indebted to the initial work of James McGrath, an amateur whose work is the basis for our understanding the lichen distribution within Pennsylvania. Robert J. Hill facilitated the inclusion of this contribution in the present Proceedings.

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