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Diversity, dispersal and biogeography of bryophytes
(mosses)
Jan-Peter Frahm
Originally published in the journal Biodiversity and Conservation, Volume 17, No 2, 277–284.
DOI: 10.1007/s10531-007-9251-x � Springer Science+Business Media B.V. 2007
Abstract Bryophytes disperse by small unicellular spores between 7 lm und usually less
than 100 lm. A large percentage of species is sterile and propagates vegetatively either by
special brood bodies or fragments of whole plants. It is shown that there is no difference in the
effectiveness between generative and vegetative propagation. Size and weight of the diaspores
suggest that both must easily be dispersed and the species must therefore have wide ranges.
This does, however, not result in ubiquitous occurrence. This is only true for part of the species.
Many, even sterile species show wide transcontinental ranges. On the other hand, there are
many examples of limited to very limited distribution in spite of a rich production of diaspores.
These are explained by narrow ecological niches, age of taxa, local extinction or historical
events such as ice ages. Conspicuously, species can loose the ability for dispersal for unknown
(perhaps genetic) reasons, which may ultimately lead to extinction.
Keywords Bryophytes � Dispersal � Vegetative propagation � Spore dispersal �
Endemism � Relics � Ubiquitism
Introduction
Bryophytes are the second largest group of green land plants and the only haploid land plants.
They are presumably polyphyletic and do no exist as natural group, similarly so as ‘‘algae’’,
but are composed by mosses (Bryophyta), liverworts (Marchantiophyta) and hornworts
(Anthocerotophyta). Although very different in structure, they correspond, however, in their
life cycle. Like ferns and allies, they are spore plants. In contrast to spermatophytes, they
distribute a single cell with a haploid genome, but usually in masses. Seed plants, in contrast,
distribute a diploid embryo in a seed, variously packed in a fruit. Spermatophytes have thus
Special Issue: Protist diversity and geographic distribution. Guest editor: W. Foissner.
J.-P. Frahm (&)
Nees-Institut fu¨r Biodiversita¨t der Pflanzen, Rheinische Friedrich-Wilhelms-Universita¨t Bonn,
Meckenheimer Allee 170, 53115 Bonn, Germany
e-mail: frahm@uni-bonn.de
W. Foissner et al. (eds.), Protist Diversity and Geographical Distribution
DOI: 10.1007/978-90-481-2801-3_4 43
taken an alternative evolutionary pathway, which was by far more successful than the tra-
ditional spore dispersal (Frahm 2001).
Bryophytes can therefore be used as a model organism for spore plants. Bryophyte spores
are produced in sporangia (‘‘capsules’’). The spores are between 7 and 100 lm, max. 200 lm
large, on average 10–20 lm. They are released in quantities between 4 and 5 millions per
sporangium, usually several hundred thousands. The smaller spores (\25 lm) can easily be
lifted into the atmosphere by warm air and distributed by air currents globally. There is,
however, no doubt that also the larger spores can be transported over large distances by
stronger winds or attached to animals. Spores are thus ubiquitous, they are also dispersed into
regions in which the species cannot grow. This is shown by large sand or clay pits in central
Europe, in which occasionally arctic species are found. An analysis of spores in rain water of a
meteorological station in Finland revealed that there were spores of Aloina brevirostris, a
species not known from Finland (Petterson 1940). The overall presence of spores is one of the
reasons for the use of bryophytes as indicators for climate changes: spores of southern species
are dispersed across the former borders of their ranges and can react immediately upon a
warmer climate (Frahm and Klaus 2001). In addition, these spores can keep their vitality for
more than 100 years. As an example, several rare moss species usually typical for xerothermic
vegetation were found on loess soil along the edge of a forest south of Bonn. The rarity of
these species, of which some have never been found in this region or not for 100 years, made
it unlikely that they arrived by recent spore dispersal. It turned out that there were vineyards in
this region before 1880 and that they were given up and forested as a consequence of the
phylloxera disease (Frahm 2006).
The high potential for generative and vegetative propagation of bryophytes may lead to
the assumption that all bryophytes have large ranges. This is not the case. In spite of the
facility to spread very easily, many bryophyte species have very limited ranges.
Diversity
Bryophytes are a group of about 15,000 species. Traditionally, the species number was
indicated in textbooks with 25,000 species, which seems to be a count of all species
enumerated in the bryophyte volumes of Engler-Prantl´s ‘‘Natu¨rliche Pflanzenfamilien’’.
Recent worldwide monographs and revisions have distinctly reduced the number of spe-
cies. Reason is especially that many species have large, for instance pantropical ranges,
and have been described repeatedly from different parts of the tropics under different
names. In the nineteenth century, the religious convictions of some authors did not allow
the idea that a species occurs on different continents because they were assumed to be
independently created by god. In contrast to other organisms, the number of bryophytes is
decreasing (also and especially in the tropics) because more species are reduced into
synonymy then described as new. For this reason, bryophytes provide a good base for
calculation of biodiversity because they give approximate species numbers.
Dispersal
Vegetative dispersal
Two thirds of the mosses are dioecious. A fertilisation of the female egg is only possible if
male plants are in close contact. The spermatozoids can swim only over a short distance
44 W. Foissner et al. (eds)
and rain drops with spermatozoids can hardly reach more than one meter. If a male spore
lands somewhere, it establishes a male clone, which will not have any chance for sexual
propagation until it gets in contact with a female clone. To cover the time span in between
sexual propagation, both sexes propagate asexually. The need for an asexual strategy of
propagation has led to an enormous variety of different structures for this purpose amongst
bryophytes. Basically, every part of a bryophyte plant can reproduce vegetatively (rhizoids,
leaves, stems).
However, only part of the species produce spores. Many species are only known in
sterile condition. This depends often on the lack of one sex. There is, however, hardly any
difference in the size of ranges between sterile and fertile species. As

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