Bryophytes: Encyclopedia Arctica 5: Plant Sciences (General)

Author Stefansson, Vilhjalmur, 1879-1962


(EA-PS. William Campbell Steere)



Scroll Table to show more columns

Classes of Bryophytes 3
Musci 4
Spagna 6
Hepaticae 8
Anthocerotes 9
Distribution of Arctic and Subarctic Bryophytes 9
Arctic Alaska and the Yukon 10
Canadian Western Arctic 11
Canadian Eastern Arctic 12
Greenland 13
Iceland 14
Spitsbergen 15
Jan Mayen 15
Northern Scandinavia 16
Franz Josef Archipelago [: ] 17
Severnaya Zemlya Archipelago 17
Soviet Arctic Mainland 17
General Considerations 18
Bryophyte Associations in the Arctic 22
Problems in Arctic Bryology 24

EA-Plant Sciences (William Campbell Steere)

Mosses and liverworts (bryophytes) are small plants that as individuals would scarcely be noticed. However, since they usually grow in tufts or mats, they contribute much, in the aggregate, to the green color of forests, moun– tains, and moors, especially in rainy weather. The association of mosses with moist habitats is no accident, since none of these plants has true roots, and they can, therefore, get little water from below the surface of the soil. They need abundant moisture not only for their ordinary vegetative growth, but also for their reproduction. Although a few mosses are able to live on rocks exposed to the sun in deserts, and may not receive water more than a few times a year, the great majority of them grow in moist places, and it is very obvious to any observer that the moister the climate, the more abundant are the mosses and liverworts.
In mountain forests where clouds hang low at night, or where mist and rain are of almost continual occurrence, so that the air is saturated with moisture during at least part of each day, mosses become so conspicuous that this type of vegetation is known to botanists and to geographers as a special type, the “mossy forest.” Mossy forests are found on the coastal ranges of the Pacific Northwest of North America, where mosses clothe the trees and hang from them in festoons, and may even become weeds in fruit orchards. In the wet forests of tropical mountain peaks, mosses are so abundant that the apparent diameter of tree trunks is doubled by their growth, and even the leaves may be covered with liverworts and mosses. In arctic regions, where there are no

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forests, the abundance of mosses clothing rocks and ledges is directly related to the amount of precipitation and humidity.
Mosses are very hardy plants and can resist extremely unfavorable condi– tions. As one ascends a high mountain, he finds mosses and liverworts cover– ing the rocks and the ground long after the disappearance of trees, and these plants which appear so delicate have been collected at altitudes as great as 18,000 feet above sea level in the Himalayas and in the Andes of South America. Likewise, as one goes north in Europe, Asia, and North America, he finds that, in many areas beyond the tree line, mosses may become the most conspicuous land plants, as well as the most numerous in species. For this reason, they are among the very few plants which flourish on the Antarctic Continent.
A curious and interesting fe ^ a ^ ture of mosses is that the plants will revive when moistened, ever after years of drought. Cells from leaves dried care– fully for many years, when well soaked up, cannot be distinguished easily under the microscope from fresh ones. The question as to whether or not these old dried leaves are still alive has never been answered.
The ability of mosses to withstand not only low temperatures but also desiccation means that they can invade freshly exposed rock surfaces, which they gradually break down into soil, thereby preparing the way for larger plants. This ability also enables them to grow as far northward as land goes, to beyond 83° N. latitude on the northern end of Greenland, where temperatures are very low in winter but relatively high in summer, where there [: ] is no night during part of the year and no day during another part, and where they are frozen solid for several mo ^ n ^ ths and then perhaps dried out during part of the summer.

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Although all these conditions do not prevail on the summits of high mountains, there is nevertheless some basis for comparing alpine and arctic regions, especially since many species grow in both places. One of the best analyses has been made recently by Meylan (67) who says (translated): “The bryological vegetation of Iceland, especially that of the regions situated at some altitude, seems analogous to that of the alpine meadows of our own Alps, especially to that of the little snowy valleys in siliceous areas. Much affinity is found likewise with our high altitude bogs. The carpet of mosses in Iceland seems to develop, even more than in the Alps, brown and purple coloration.
“Even though the rigorous climate of Iceland seems to cause an especially vigorous development of some species, these conditions provoke in [: ] the major– ity of species a diminution of growth and the formation of depauperate forms. This phenomenon is especially visible in Hylocomium. One sees that these species lack the shelter of the forest.
“The same phenomenon is observed as one ascends the Alps in the nival zone, and one may note the same causes producing the same effects, a perfect parallelism between these depauperate forms of arctic regions and those of the elevated regions of our Alps. It is possible to present numerous examples of this parallelism; I cite for the Acrocarpae only the Syntrichia, especially S. ruralis . In general, in Iceland, as at 3000 meters altitude in the Alps, the stems of this species scarcely reach 1 to 1.5 cm.; the shorter leaves are no longer squarrose, but erect like those of S. montana .”
Classes of Bryophytes
Mosses and liverworts fall into several groups, on the basis of structure and reproductive behavior. The four classes are: ( 1 ) the true mosses, Musci;

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( 2 ) the peat mosses, Sphagna; ( 3 ) the true liverworts,Hepaticae; and ( 4 ) the hornworts, Anthocerotes.
Musci . True mosses are always green, and therefore are all able to make their own food. The individual plants range insize from nearly invisible to the naked eye to more than a yard long, and consist of a creeping, hanging, floating, or erect stem, covered with delicate, scalelike leaves. Mosses have no true roots and must, therefore, depend for water absorption on small, threadlike tubes, the rhizoids, that absorb moisture from the surface of the soil or from the atmos– phere. For this reason, mosses are able to grow more or less continuo o ^ u ^ sly through the winter, when temperatures at midday rise to the thawing point, since they can use a superficial film of water not available to the roots of higher plants frozen fast in the ground. Most of the water used by mosses passes up the out– side of the stem, by capillarity, through and over the layer of rhizoids which covers the stem, and the height of an erect moss stem is apparently determined by the height to which water will rise by capillary action.
In the [: ] tropical and temperate mossy forests, water is obtained from the saturated air, so that banners of mosses a yard long, hanging from the twigs and branches of trees, are not uncommon. Likewise, mosses growing in run– ning water may develop very elongated stems which steam out for a yard or so with the current. In contrast to the wet foresttypes, arctic mosses usually have rather short stems because of the generally reduced rainfall and the drying winds. The leaves of almost all mosses are only one layer of cells thick, in striking contrast to the complex leaves of higher plants, which are usually well-protected against evaporation, but which are killed at once if dried.
Mosses do not produce seeds, but much simpler, single-celled reproductive bodies, the spores. The spores are very small and very light, so ^ that ^ they float in

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the atmosphere with only a slight movement of air, and have therefore been found at very high altitudes in samples of air taken by airplanes. Each moss plant produces hundreds of spores, and when one consider [: ] ^ s ^ the large numbers of indi– vidual plants of weedy species of mosses, he begins to realize the astronomical numbers of spores released into the air during any one year. The spores may live for years in some mosses, but in others they die almost at once if they do not land in a suitable spot, just as with the seeds of higher plants. Moss spores, however, need light for germination.
Mosses need water for fertilization, since the sperms are free-swimming, just as in algae and in ferns. From the fertilized egg comes the spore-bearing structure of a moss, consisting primarily of a usually cylindrical spore case, supported on a threadlike stalk, embedded at its lower end in the green plant from which it derives its moisture more or less parasit u ^ i ^ cally. Although mosses depend on water for their [: ] ordinary life processes, and water is indispensable for fertilization, mosses do live mostly on land and often in relatively dry places. The other great advance of mosses over algae, in an evolutionary sense, is their conspicuous development of alternation of generations, in which a spore-bearing plant, the sporophyte, with a diploid chromosome number, lives dependently on the gamete-producing leafy green plant, which has a single set of chromosomes. The obligate alternation of generations, with periodic doubling and halving of chromosome number, is found in all higher plants.
Long-lived perennial mosses will produce a new set of sporophytes each year and hundreds of spores, so that the persistence of most species is assured. Other mosses, however, such as those which develop in summer on the mud flats along receding rivers, may complete their whole life cycle in a few weeks. The green plants appear, produce simple spore cases which break open and distribute

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the spores on the mud ready for another favorable season. Such annual mosses are rather rare and so small that they are difficult to [: ] find, supporting the common belief that mosses are delicate and short-lived plants. Some mosses rarely produce spores, and this situation is especially pronounced in the Arctic. Propagation is carried on by the production of detachable buds which are carried about by wind, water, or other agencies. The method of reproduction of many arctic mosses is completely unknown.
Sphagna . Peat mosses, all belonging to the genus Sphagnum , of which perhaps 100 species exist in the whole world, are among the most absorbent of all plants, since their leaves consist of large, bubble-like, dead, water-storage cells which alternate with the narrow, green, living cells. The stems and branches likewise contain special water-storage cells. These large and empty cells re– flect light and cause peat mosses to appear white when dry, so that one who knows peat moss about the greenhouse or garden is apt not to recognize it in the bog when it is green, healthy, and filled with water. The absorbent powers of Sphagnum are so great that it is used to hold moisture in dry soils, to root cuttings, to pack seedlings and cuttings for shipment, and even to ship clams and other aquatic animals which otherwise die in the absence of water.
[: ] Sphagnum possesses another curious property in addition to its great absorptiveness — it prevents the growth of many bacteria, and is, therefore, somewhat antiseptic. For this reason it was used in enormous quantities during World War I for filling absorbent bandages, because of a cotton shortage. A striking demonstration of the antiseptic properties of Sphagnum and of the peat that it produces is that people and animals who have fallen into bogs in Ireland have been found rather perfectly preserved, perhaps hundreds of years later, upon

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the draining of the bog and cutting peat into blocks for fuel.
The tips of the peat-moss plants grow each year and branch, so that a tufted growth is produced. As the plants grow upward, the deposit of dead material below them, or peat, is made deeper, and it may eventually reach a depth of many yards. In flat land, where bogs form over springs, the bog may become much higher than the surrounding country, because of the growth of the Sphagnum , and the water is held within the bog in enormous quantities. In Europe, the break– ing out of one of these raised bogs because of excess rainfall may flood much of the surrounding country.
The reproduction of Sphagnum is the principle exactly like that of the true mosses. The sporophyte, however, is much simpler, consisting only of a spherical spore case without a stalk. In the warm rays of the summer sunshine, the air within the mature capsule expands and finally develops enough pressure to blow off the lid and the entire mass of spores in one puff. If plants of Sphagnum with many brown, spherical capsules be brought into a warm, dry place, the bursting open of the spore cases can be heard clearly, like the popping of corn on a small scale.
Peat is used in many countries for fuel, and although this is not so extensively the case in the New World, there are nevertheless in North America millions of tons of it available in case of emergency, and it is the potential source of hydrocarbons for many purposes. It is a standard fuel for heating and [: ] cooking in many parts of northern Europe, although it does not give off nearly as much heat as coal does, and it has a peculiar odor when burning. When peat is compressed, it produces coal, and the idea has been proposed that our present coal deposits came from peat bogs of extremely ancient times. This idea is well supported by the discovery of Sphagnum leaves and spores in coal

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from the Rocky Mountains and from Greenland.
Hepaticae . Hepatica is the Latin word for liver, and it was applied to certain plants during the Middle Ages because of their liver-shaped leaves or plant bodies. In [: ] medieval times, medicines came [: ] almost entirely from plants, and were sometimes chosen according to a curious superstition. It was assumed that a benevolent Creator would mark or “sign” each plant in some way to indicate its usefulness to man. According to this pious “doctrine of si [: ] gnatures,” yellow turmeric was used to treat jaundice, plants with heart– shaped leaves were used for heart diseases, and the liver-shaped plants described here became known as liverworts or hepatics and were widely prescribed for liver ailments.
The name “liverwort” was applied by early botanists only to plants without a leafy stem, and that consist of a flat, ribbon-like or somewhat liver-shaped body of green tissue, called a thallus. However, this original concept has been extended to include many leafy forms which had been originally placed with mosses, so that now the true “liverwort” type makes up only about 15 per cent of the Hepaticae, of which the remainder have leafy stems instead of a thallus.
Leafy liverworts always possess two rows of leaves and are usually con– spicuously flattened against the soil, rotten wood, or rock upon which they grow. Some kinds have a third row of somewhat different leaves, the underleaves. Leafy liver ^ w ^ orts may be distinguished from mosses by the two-rowed leaves, the lack of a midrib in the leaves, and the fact that the leaves are often variously deeply lobed or toothed. In mosses, the leaves are arranged spirally around the stem, usually have a midrib, and are never lobed or deeply toothed. Further– more, the structure of liverworts is much more delicate than mosses, and they do not withstand the rigors of drought and cold in the Arctic Zone as well as

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mosses do. Nevertheless, most liverworts are perennial and produce spore cases each year in abundance under favorable conditions.
Liverworts reproduce in exactly the same way as do mosses, by the ferti– lization of an egg, and the subsequent development of a diploid spore-producing structure from the fertilized egg. The developing sporophyte of all Hepaticae reaches its full size inside the greatly stretched archegonium that [: ] produced the egg. When the spores are mature and ready for distribution, they may be re– leased by the bursting of the spore case within the archegonium, but usually the telescoped cells below the spore case suddenly elongate and thrust the spore case out through the top of the archegonium and into the air on a stalk that is sometimes several inches long.
Anthocerotes . The [: ] Anthocerotes are a small group of rather rare liverworts, sometimes called the hornworts because of the elongated cylindrical, pointed sporo– phyte, which has the peculiar property of being able to continue growth through– out the growing season by means of a region of dividing cells at the base. As the sporophyte splits open at the top and mature spores escape, new cells are being produced at a bottom. This curious manner of growth of the spore-producing structure has led to many theories that this group might ^ be ^ in some way the “missing link” from which higher plants developed, since all higher, or vascular, plants as we know them are spor ^ o ^ phytes which continue growth throughout much of their lives.
Distribution of Arctic and Subarctic Bryophytes
As has been pointed out, mosses and liverworts are able to survive extremes of climate and local environment which most higher plants cannot tolerate. Consequently above the timber line on mountains and north of the tree line in both hemispheres,

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the dominant plants in numbers of species, and even of individuals are often bry– ophytes. Nevertheless, these plants are not sufficiently collected, and are too often overlooked in ecological and floristic studies. It is not uncommon for a detailed study of nearly any phase of arctic botany to omit a consideration of the bryophytes altogether, even though this group is represented in every arctic region by as many species as the higher plants. As an illustration, one may take the most recent large publication on arctic plants. The Botany of the Canadian Eastern Arctic , published by the National Museum of Canada. In this important work, a whole volume (408 pages) is devoted to 297 species of vascular plants, whereas less than 150 pages cover 304 species of mosses and 78 spe [: ] ^ c ^ ies of hepatics. The writer believes that the high specialization of bryophytes to their habitat and their significance as indicators of edaphic and environmental factors have not been properly realized by botanists, at least in the Arctic.
During the last decade, mosses have come into general use as indicators of forest sites and to help determine the stages of succession or stagnation in forests and moors, especially in Scandinavia (20;91). The extension of this important technique to North America and to the arctic regions of both hemispheres is highly desirable.
Arctic Alaska and the Yukon . Although no organized account of the bryophytes of arctic Alaska and the Yukon has yet been drawn up, we have a fair idea of the composition of that flora through several publications based on reasonably large collections, especially the papers of Hooker and Arnott (45) on Kotzebue Sound; Williams on the Yukon (95) and on the arctic coast of Alaska (96); and Persson (73;74) on miscellaneous collections from the Bering Strait region and from the Yukon. Although the coastal regions of Alaska south of and including the Aleutian chain are extremely rich in bryophytes and have many species which are either endemic

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or of an unusual pattern of geographic distribution, arctic Alaska presents the usual group of circumpolar species of wide distribution. A rough estimate of the number of bryophytes of this region would be perhaps 100 species of Hepaticae and about 300 species of Musci, including the Sphagna. In spite of [: ] the large number of widespread circumpolar species, there is a surprisingly large element of species restricted to this segment of the Arctic, some of which are endemic, others of which are at their northern extreme in the Rocky Mountains. Examples are Diplophyllum imbricatum , Lepicolea fryei , and Bryobrittonia pellucida . As a result of many col– lections made during World War II, and of a new interest in the flora of Alaska and the Yukon, this almost unknown region is gradually becoming better understood. The presence of many areas which have escaped glaciations, and which, therefore, have served as refugia for plants during continental glaciations, should serve as a sti– mulus for extensive and critical study of the flora.
Canadian Western Arctic . Perhaps the most unknown area, bryologically, of northernmost North America is the arctic coast between the mouth of the Mackenzie River and the Boothia Peninsula, as well as the islands of the American Arctic Archipelago lying north of it, including especially the larger islands, as Victoria, Banks, Melville, and Parry Islands. This region, which may be called the Canadian Wes– tern Arctic, has been little explored by botanists and lacks the comprehensive study which has been given to the Canadian Eastern Arctic. Parry’s 1819-20 expedition to Melville Island and [: ] Franklin’s journey to the polar sea between 1819 and 1823 both resulted in important collections of bryophytes. Except for the relatively large collection of bryophytes made by the Canadian Arctic Expedition of 1913-18 on the [: ] arctic coast and Victoria Island (96), further bryological material from the Canadian Western Arctic is composed mostly of small collections made incidentally

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to other work. The first-known American specimens of such Siberian and Scandi– navian species as Radula prolifera , Campylium zemliae , and Bryum neodamense came from this region. Described as new from this area were Polytrichum hyperboreum , Bryum calophyllum , B. arcticum , and Barbula johansenii of which all but the last are now known to have circumpolar ranges. Although only about a hundred Musci and perhaps a dozen Hepaticae have been reported from the Canadian Western Arctic, it will probably be discovered to be as rich in species as the regions east and west of it, upon proper exploration and study.
Canadian Eastern Arctic . The bryophyte flora of the Canadian Eastern Arctic is relatively better known than the other arctic American floras, primarily through the enormous collections resulting from the second expedition of the Fram (18). Other large collections made more recently by Freuchen, Polunin, Dutilly, and other have made known to a greater or lesser extent the bryophytes of nearly every major area of the region (41;87;88). As the result of the extensive collections now available, it has been possible to summarize rather completely [: ] the bryophyte flora of the Canadian Eastern Arctic, north of 60° N. latitude (90). The total of 304 species of Musci and 78 of Hepaticae (77) is not surpassed by the known bryo– phyte floras of many temperate regions far to the south, many of the United States, for example. A study of these materials demonstrates a very definite high-arctic ele– ment in the bryophyte flora — species which flourish as far north as land exists, to beyond latitude 82° N., yet which gradually disappear southward and are scarcely to be found south of 60° N. latitude. Examples are Distichium hagenii , Arctoa hyperbo rea , Stegonia latifolia , Voitia [: ] hyperborea , Haplodeon wormskjoldii , Mieli chhoferia macrocarpa , [: ] Pohlia crudoides , Bryum obtusifolium , B. globosum , Cin clidium subrotundum , C. arcticum , Aulacomnium acuminatum , A. turgidum , Conostomum boreale , Drepanocladus berggrenii , and Hygrohypnum polare . Many [: ] other species are

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able to exist in latitudes as northerly as the truly arctic species just listed, but also occur in alpine habitats far to the south. These species, the arctic– alpine species, have received considerable att [: ] ^ en ^ tion, especially in the southern extension of their range, since they are not rare at higher elevations in the relatively well-studied temperate latitudes, and a list of them would be too long to give here. Nevertheless, it is important to point out that the arctic-alpine species are with few exceptions circumboreal in their distribution.
Greenland . The bryophytes of Greenland are known not through any one or more large collections as are those of Siberia and Arctic America, but through multitudes of relatively small gatherings. Travel is difficult and distances are great in an island that is almost two thousand miles long and [: ] that ex– tends from below 60° N. latitude nearly to 84° N. latitude. Consequently, al– though dozens of collections have been made through casual or intensive study of small areas, no over all study of the whole island has been made in the field of bryophytes. Unfortunately for our purposes here, there has been no comprehensive review since 1880 of specimens and publications resulting from all the different collections. That is something much to be desired. The volumes of Meddelelser om Grønland contain many small contributions to the bryological flora of Greenland, so that some general remarks may be made. In a very general way, one finds a relationship between the bryophytes of southern Greenland, whose climate is tem– pered by the Gulf Stream, and those of southern Iceland. One of the most inter– esting indications of this affinity was the recent discovery of Bryoxiphium norvegi cum in East Greenland. The [: ] greater part of the flora of East Greenland seems to have a closer relationship with that of northern Iceland and other areas to the east than with the American Arctic Archipelago to the west. Western Greenland, on [: ] the other hand, shows in its bryophyte flora a definite agreement

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with that of Ellesmere, Devon, and Baffin Islands to the west. Approximately 150 species of Musci and perhaps 50 species of Hepaticae have been reported from Greenland, and it is probable that further collecting by trained bryologists will double this total from the whole island. Except for numerous species of Bryum (see p.000), the bryophyte flora of Greenland seems peculiarly lacking in endemic species. Although the specific name groenlandicum is not unusual, nearly all the species of bryophytes which bear it seem now to have a more or less wide circumpolar districution. A fact of especial interest is that in Greenland bryophytes reach their northernmost geographic extension, above 83° N. latitude, whence many species have been reported.
Iceland . The bryophyte flora of Iceland is now reasonably well known in its general outlines, even though every new collection of any size seems to contain species not previously reported. The excellent treatment of Icelandic bryo– phytes by Hesselbo (39) and the recent report on a large collection by Meylan [: ] (67) give us much more material for bryogeographical considerations than is avai– lable from most northern lands. A total of about 100 Hepaticae, more than [: ] 20 Sphagna, and nearly 350 species of Musci have been reported. Because of its position just south of the Arctic Circle, the sweep of the Gulf Stream along its south coast, and the numerous hot springs, Iceland supports a surprisingly temperate bryophyte flora, at least in certain restricted localities. Many European species reach their northern limit of distribution here, as Anthoceros punctatus , Fossombronia dumortieri , Blasia pusilla , Archidium phascoides , Mnium hornum , Atrichum undulatum , Entosthodon ericetorum , and Campylopus fragilis . One of the most interesting species in the flora of Iceland is Bryoxiphium norvegicum , which in spite of its specific name is not known from Norway, but has a curious geographical distribution in unglaciated regions of North America

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and also occurs in Mexico and the Orient (89). Endemic species seem to be few, among which are Bryum islandicum , B. groenlundii , and Fontin e ^ a ^ lis islandica .
According to Hesselbo (39), the vegetation of Iceland corresponds in its composition most nearly with that of Scandinavia and South Greenland. All species so far listed from Iceland, except for the Bryoxiphium just mentioned, are also found in Scandinavia. Meylan (67), however, expresses the opinion that the bryological flora of Iceland is related directly to that of north and central Europe, since no purely American species are found there, but only American species which are also common to Europe.
Spitsbergen . Numerous recent collections have added some species to the known bryological flora of Spitsbergen, but our main knowledge concerning the bry– ophytes of these islands still depends largely on the excellent work of Berggren (12) and Arnell (2). In view of the isolated position and high latitude of the Spitsbergen group, the bryophyte flora is surprisingly large, with over 200 species of Musci and 50 of Hepaticae - more than have yet been found in Greenland. Although numerous species have been described from Spitsbergen, and this name serves as the basis for several specific epithets, most, if not all of them, have now been found elsewhere in the Arctic. Since the bryophytes are of distinctly arctic and arctic-alpine types, [: ] with a characteristic circumpolar geographic districution, it is difficult to correlate the flora of Spitsbergen with [: ] that of any other polar region. However, it seems about equally close to that of Greenland and northernmost Scandinavia.
Jan Mayen . Jan Mayen is an isolated arctic island which is seldom visited by botanists. According to the most recent summary of its bryophyte flora (60;61), 39 Hepaticae and 106 Musci have been collected there. This surprisingly large

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number of species indentified from so small an island may in part be due to the fact that a bryologist has visited it. In spite of the high latitude (about 71° N.), the flora seems not to be essentially arctic, but more related to that of Iceland or Norway, through the large number of boreal species.
Northern Scandinavia . Northernmost Norway, Sweden, and Finland con– statute by far the best-known region lying so far north in the world, from a bryo– logical viewpoint. Although its flora may not have the potential richness of the Soviet Arctic, counting both European and Asiatic northern extensions, the bryophytes of Scandinavia have been so thoroughly collected and studied that perhaps twice the number of species have been found north of the Arctic Circle there than anywhere else. Furthermore, the warm Gulf Stream which runs northward along the Norwegian coast gives opportunity for a genuinely temperate [: ] flora to exist in a region that lies latitud ^ i ^ nally quite far north, thus bringing into the area under consideration many species which would otherwise not be able to flourish there. Through the studies in Norway of Hagen (32) and Jørgensen (57), in Sweden by Arnell and Jensen (9), and in Finland by Brotherus (14), as well as the [: ] comprehensive treat– ments of the bryophytes of all Scandinavia by Arnell (4) and Jensen (55), the astonishing totals of more than 500 species of mosses and perhaps 200 species of hepatics have been reported from northern Scandinavia. The enormous collections and the careful studies in localized areas give adequate data for careful bryo– geographical studies, so that among the bryophytes of the Sarekgebiet of Sweden, for example, Arnell and Jensen (9) have recognized with some confidence 6 major floristic elements and a dozen minor ones. Furthermore, the understanding of bryophytic associations in each habitat is so exact that it sets a model for bryocoenological studies in other regions.

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Franz Josef Archipelago . The group of islands which make up the Franz Josef Archipelago have remained almost totally unknown with regard to their bryophyte flora until relatively recently, when two important collections were made by Ivanov in 1929 and by Savicz in 1930, during expeditions of the Soviet icebreaker G . Sedov (81;82). The 7 Hepaticae and 80 Musci now known from these islands con– sist mostly of common arctic species of wide distribution, and seem to include no endemic species. The affinity of this flora is difficult to determine because of the small number of species concerned and their wide distribution. However, there are some indications that it is most closely related to the flora of northern Scandinavia and Siberia.
Severnaya Zemlya Archipelago . The bryophyte flora of [: ] this botanically little-known area consists of only 16 species of mosses and 1 hepatic, all of them species of wide distribution and not uncommon on the Siberian mainland to the south as the [: ] result of the 1930 expedition of [: ] the Russian icebreaker G. Sedov (82).
Soviet Arctic Mainland . The mainland of the Soviet Arctic, taking together the European and Asiatic segments, including Novaya Zemlya, probably has the richest bryophyte flora, at least potentially, of any of the arctic regions. This opinion is based on the fact that three great north-flowing rivers, the Ob, the Yenisei, and the Lena, all serve as routes to bring species north from more temperate regions. Furthermore, the great land mass to the south, representing very differ ^ e ^ nt floras in widely separated regions, both in Europe and Asia, serves as an enormous reservoir of species which in some way may find or have found their way to the Arctic. Arnell, in 1875 and 1876, collected nearly 100 species of Hepaticae and over 400 species of Musci in the valleys of the Ob and Yenisei rivers (64;65). In 1898, Nilsson-Ehle collected 61 Hepaticae, 14 Sphagna, and 233 Musci in the valley of

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Lena (8). Kjellman, botanist to the Vega expedition along the arctic coast of Russia and Siberia, brought back about 60 Hepaticae, 12 Sphagna, and over 150 Musci (5). These splendid collections give an excellent indication of the richness of the bryophyte flora of arctic Russia and Siberia and are very use– ful in charting the total distribution of arctic species. In the present state of our knowledge concerning arctic bryophytes, it is difficult to determine if the large num ^ b ^ er of species endemic to Siberia depends on the narrow specific concepts of the bryologists who described them, or upon the intrinsically richer flora. Since many of these species have now been found in arctic North America, as Aulacomnium acumiaatum , Cinclidium latifolium , Dicranum fragilifolium , Diplophyllum microdontum , and Radula prolifer ^ a ^ , it is probable that the latter alternative is the correct one. There still remain many species restricted to Siberia, as Scapania rufidula , Calycularia laxa , Scouleria rschewini , Myrinia rotundifoliu , Dicranum tundrae , and Didymodon rotundatus .
General Considerations
A striking feature of truly arctic mosses, to be seen from the foregoing discussions of different areas and from the tabular depiction of geographical ranges (see Table I), is that a large number of them are circumpolar. The relatively low degree of endemism, and the fact that many of [: ] those species long considered to be endemic have now been discovered in other and widely sepa– rated areas, leads naturally to the opinion that careful collection and study in the future will [: ] greatly extend the range of almost all polar species of bryophytes. The recent discovery in the American Arctic of Siberian species with a very limited distribution, as Radula prolifera , Dicranum fragilifolium ,

[: ] EAPS Steere: Bryophytes

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TABLE I. Known Distribution of some Arctic and Subarctic Bryophytes. Key
1. Arctic Alaska 10. Jan Mayen
2. Canadian Western Arctic 11. Northern Scandinavia
3. Canadian Eastern Arctic 12. Franz Josef Land
4. Ellesmere Island 13. Severnaya Zemlya
5. Baffin Island 14. Novaya Zemlya
6. West Greenland 15. Yenisei region
7. East Greenland 16. Lena region
8. Iceland 17. Alps and Rockes
9. Spitsbergen

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Plant 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Anthelia julaces * * * * * * * * * *
A. Juratzkana * * * * * * * * * * * *
Arnellia fennica * * * * * * * *
Cephaloziella verrucosa * * * *
C. divaricata v. incurva *
Clevea hyalina * * * * * *
Gymnomitrium concinnatum * * * * * * * * * * * *
G. corallioides * * * * * * * * * * * * * *
Jungermannia polaris * * * *
Lophozia groenla [: ] ndica * *
L. murmanica * * *
Marsupella groenlandica * * * *
Mesoptychia sahlbergii * * * *
Odontoschisma macounii * * * * * *
Peltolepis grandis * * *
Plagiochila arctica * * * * *
Pleuroclada albescens * * * * * * * * *
Prasanthus suecicus * * * * *
Radula prolifera * * * *
Sauteria alpina * * * * * * * *
Scapania simmonsii * * *
S. spitsbergensis * * * * * *
Temnoma setiforme * * * * * * * * * * * *
Andread blyttii * * * * * *
A. obovata * * * * * *
A. papillosa * * * * * * * * *
Aongstroemia longipes * * * * * *

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Table I continued
Plant 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Aulacomnium acuminatum * * * * * * *
A. turgidum * * * * * * * * * * * * * * *
Brachythecium turgidum * * * * *
Bryum archangelicum * * * * * *
B. arcticum * * * * * * * * * * * * * * *
B. globosum * * * * * * * *
B. obtusifolium * * * * * * * * * * * *
B. rutilans * * * * * * * * * * * *
Calliergon turgescens * * * * * * * * * * * * * * *
Campylium zemliae * * * * *
Cinclidium arcticum * * * * * * * * *
C. latifolium * * *
C. [: ] polare * * * *
C. subrotundum * * * * * * * * * * *
Conostomum boreale * * * * * * * * * * * * * *
Cratoneuron curvicaule * * * * * * * *
Desmatodon suberectus * * * * * * * * *
Dicranum angustum * * * * * *
D. arcticum * *
D. elongatum * * * * * * * * * * * * * *
D. fragilifolium * * * *
D. hyperboreum *
D. neglectum * *
Didymodon rufus * * * * * * * *
Distichium hagenii * * * * * * * *
D. inclinatum * * * * * * * * * * * *
Ditrichum flexicaule * * * * * * * * * * * * * * * * *
D. giganteum * *
Drepanocladus badius * * * * * * * * * * * * *
D. berggrenii * * * *
D brevifolius * * * * * * * * *
D. latifolius * * * * * * * * *
D. tundra * *
Fissidens arcticus *
Funaria Polaris * *
Haplodon wormskjoldii * * * * * * * * * * * *
Hygrohypnum polare * * * * * * * * * * *
Hypnum revolutum * * * * * * * * * * * * * * * *
Mielichhoferia macrocarpa * * * *
Myurella tenerrima * * * * * * * * * * * * *
Oligotrichum incurvum * * * * * *
Oncophorus schisti * * * * * *
Orthothecium acuminatum *
O. chryseum * * * * * * * * * * * * * * * *
Orthothecium strictum * * * * * * * * * * * * * *
Orthotrichu [: ] m killiasii * * * * * * * * * *
Philonotis tomentella * * * * * * * * * * * * *

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Table I continued
Plant 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Polytrichum fragile * * * *
P. hyperboreum * * * * * * * * * * * *
P. jensenii * * * * * * * * *
Pottia heimii, v. obtusifolia * * * * * * * * * * *
Psilopilum cavifolium * * * * * * *
P. laevigatum * * * * * * *
Rhacomitrium lanuginosum * * * * * * * * * * * * * * * *
Scouleria rschewini * *
Seligeria Polaris *
Spalachnum vasculosum * * * * * * * * * * * *
Stegonia latifolia * * * * * * * * * * *
Tetraplodon bryoides * * * * * * * * *
Timmia norvegica * * * * * * * * * *
Voitia hyperborea * * * * * * *

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Cinclidium latifolium, and Aulacomnium acuminatum , and the reciprocal discovery in Siberia of several species previously considered endemic to the American Arctic, as Scapania simmonsii and Plagiochila arctica , well illustrates this point. The generalized circumpolar geographical distribution of the arctic bryophytes seems to indicate that their invasion of the Arctic Zone was very ancient indeed, since their migration under present conditions must be exceedingly slow.
The stability of specific types is also a remarkable feature of arctic bryophytes. Although all of them show the usual response in growth to unfavora– ble environmental conditions, under the same conditions specimens form widely separated localities appear almost identical. The only govern which seem highly variable genetically are Drepanocladus and Calliergon among the Pleurocarpae, and Bryum in the Acrocarpae. Since Drepanocladus and Calliergon are represented by relatively few species, the problem is not particularly acute. Bryum , how– ever, has proliferated in the Arctic zone in much the same manner as Taraxacum , and perhaps through the same methods. Although apomictic clones are not known yet in mosses, apospory is not uncommon in them. A thorough study of the more than 100 species of Bryum in the Arctic with modern genetical and cytological techniques would produce results of the greatest scientific interest, and might clarify some of our present problems concerning specific concepts in Musci.
Bryophyte Associations in the Arctic . As bryophytes are extremely sensi v ^ t ^ ive to edaphic and climatic factors, one finds a surprisingly large series of differ– ent associations, reflecting sometimes only very small differences in habitat conditions. The absence of trees in all arctic regions removes the complicated series of forest associations, and so the factors which influence the distribu– tion and association of bryophytes are primarily the nature of the substratum, the amount of water through all or part of the year, the amount of insolation, ex– posure to wind, and temperature. In any given habitat, the amount of water seems

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to be the most important limiting factor in determining which species may exist there.
With the exception of members of the Splachnaceae, which usually grow on dung, bones, and other animal materials, the usual substrata for arctic bryo– phytes are soil and rock. Alkalinity in terms of calcium ion, and acidity in terms of hydrogen ion are factors which affect the distribution of species most conspicuously. In alkaline to neutral marches and bogs, on e finds a very different flora from that occurring in acid ones, with a strong development of such conspicuous species as Drepanocladus revolvens, Scorpidium acorpioides, Paludella squarrosa , Calliergon sarmentosum , C. turgescens , C. trifarium , Cinclidium stygium , Meesea triquetrs , and Philonotis tomentella . In acid [: ] bogs and swamps, Sphagnum species are not only the most predominant plants, but also the most actice acidifying agents. However, the greatest development of acid bogs and muskegs is in the subarctic zone, since Sphagnum is not primarily an arctic genus, and it gradually disappears northward, not only in number of species, but also in number of individuals. Sphagnum species are usually ac– companied in the Arctic Zone by (and may be replaced by) species of Dicranum, Polytrichum [: ] strictum , Aulacomnium palustre , Pohlia nutans , Calliergon stramineum , Tomenthypnum nitens , and many Hepaticae.
On soil, under mesophytic conditions, the bryophyte associations are very rich in species, especially in such genera as Polytrichum , Pogonatum , Timmia , Hylocomium , Lophozia , Cephalozia , and many others. In this habitat, the genus Bryum finds its maximum expression, and has developed specialized species which seem to fill even the [: ] most minute cological niches throughout the mesophytic formation. On more calcareous and somewhat [: ] drier soil, one finds species of [: ] Tortula, Distichium, Ditrichum, Encalypta, Myurella, Orthothecium ,

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Peltolepis, Sauteria , etc. In xerophytic habitats, especially on acid soil and rock, Rhacomitrium lanuginosum finds its greatest development, and may form a ground cover or heath several inches thick and, in some places, several miles in extent. Where conditions are too dry for Rhacomitrium to flourish, scattered tufts of Grimmia and Andreaea may be the only vegetation of any kind. In neutral of alkaline areas, species of Dicranum mixed with other bryophytes may produce thick cushions or mats on rock and soil, and form the dominant vege– tation over large areas.
One of the most characteristic features of arctic mosses and liverworts is the great mixture in which they grow. It is not uncommon to find twenty species in a clump the size of one’s hand, and this fact is emphasized by nearly all bryo– logists who have studied arctic material. Each microhabitat seems to develop its own little flora which grades into the next microhabitat, which may be only a few inches away and yet have its own group of species.
Problems in Arctic [: ] Bryology . This discussion would not be complete with– out a brief statement of some of the problems open to a bryologist in the Arctic, beyond the simple fact that a large number of species not previously reported can be added to our lists. Careful collecting by trained bryologists and their exten– sive field notes will solve many problems of phytogeographical distribution. The abundance of any particular species can be judged only by a bryologist in the field; inferences drawn from herbarium material alone can hardly be trusted, since the average collector will soon shun the common species and yet pick up the rare species every time he meets them. Relative abundance of any species may show its ecological preferences with relation to altitude and habitat, and may even give information on paths of migration.

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One of the most interesting phytogeographic problems is the determination of local distribution of rare or relict species, many of which show disjunction of geographic range to a greater or lesser degree. The effect of the rigorous arctic climate on the different species and floristic elements has never been studied as an ecological problem, but only with reference to taxonomy. Why is it that some species are extremely reduced and barely surviving, whereas others are robust and flourishing? Life forms and growth forms of arctic bryophytes need study as does even the time of fertilization and maturation of sporophyte. The physio– logical reasons for the lack of spore production by many arctic bryophytes need study, as well as their adjustment to the long, dark winter months. The success– sion of species of bryophytes in different [: ] habitats in Arctic is completely unknown. The study of natural moss communities has been reasonably well studied in north ^ e ^ rn Scandinavia but throughout most of the polar regions this important field of bryocoenology remains almost completely unstudied.
To summarize, although in arctic regions the bryophytes have often been collected casually and incidentally to flowering plants, there may actually be more species of bryophytes about which we know very little, and whose study in a detailed manner by bryologists in the field may [: ] well halp solve [: ] some of the many problems of arctic botany.
William Campbell Steere

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William Campbell Steere