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50 W. Foissner et al. (eds)
Myxomycete diversity and distribution from the fossil 
record to the present
Steven L. Stephenson · Martin Schnittler · 
Yuri K. Novozhilov 
Originally published in the journal Biodiversity and Conservation, Volume 17, No 2, 285–301.
DOI: 10.1007/s10531-007-9252-9 © Springer Science+Business Media B.V. 2007
Abstract The myxomycetes (plasmodial slime molds or myxogastrids) are a group of
eukaryotic microorganisms usually present and sometimes abundant in terrestrial ecosys-
tems. Evidence from molecular studies suggests that the myxomycetes have a signiWcant
evolutionary history. However, due to the fragile nature of the fruiting body, fossil records
of the group are exceedingly rare. Although most myxomycetes are thought to have very
large distributional ranges and many species appear to be cosmopolitan or nearly so, results
from recent studies have provided evidence that spatial distribution patterns of these organ-
isms can be successfully related to (1) diVerences in climate and/or vegetation on a global
scale and (2) the ecological diVerences that exist for particular habitats on a local scale.
A detailed examination of the global distribution of four examples (Barbeyella minutissima,
Ceratiomyxa morchella, Leocarpus fragilis and Protophysarum phloiogenum) demon-
strates that these species have recognizable distribution patterns in spite of the theoretical
ability of their spores to bridge continents.
Keywords Distribution patterns · Ecology · Long-distance dispersal · Microorganisms · 
Slime molds
Special Issue: Protist diversity and geographic distribution. Guest editor: W. Foissner.
S. L. Stephenson
Department of Biological Sciences, University of Arkansas, Fayetteville, AR 72701, USA
M. Schnittler (&)
Institute of Botany and Landscape Ecology, Ernst Moritz Arndt University Greifswald, Grimmer Str. 88, 
17487 Greifswald, Germany
e-mail: martin.schnittler@uni-greifswald.de
Y. K. Novozhilov
V.L. Komarov Botanical Institute of the Russian Academy of Sciences, Prof. Popov St. 2,
197376 St. Petersburg, Russia
W. Foissner et al. (eds.), Protist Diversity and Geographical Distribution
DOI: 10.1007/978-90-481-2801-3_5 51
52 W. Foissner et al. (eds)
The myxomycetes (also called plasmodial slime molds or myxogastrids) are a group of
eukaryotic microorganisms usually present and sometimes abundant in terrestrial ecosys-
tems. Myxomycetes have been known from their fruiting bodies since at least the middle of
the seventeenth century, when the Wrst recognizable description of a member of the group
(the very common species now known as Lycogala epidendrum) was provided by the Ger-
man mycologist Thomas Panckow. Evidence from molecular studies (e.g., Baldauf and
Doolittle 1997; Baldauf et al. 2000) indicates that the myxomycetes should be placed
within the “crown” clade of eukaryotes, which would suggest that they have a signiWcant
evolutionary history. However, due to the fragile nature of the fruiting body, fossil records
of the group are exceedingly rare. Domke (1952) described a species of Stemonitis and
Dörfelt et al. (2003) a species of Arcyria from Baltic amber dating from the Eocene,
whereas Waggoner and Poinar (1992) reported the fossil of a myxomycete plasmodium in
amber from Eocene-Oligocene deposits in the Dominican Republic. The maximum age that
could be assigned to any of these fossils would not exceed about 50 million years, which is
greater than that of the few records of fossil spores that appear to be those of myxomycetes,
which date only from the Oligocene and Pleistocene (Graham 1971).
Life cycle
The myxomycete life cycle (Fig. 1) encompasses two very diVerent trophic stages, one
consisting of uninucleate amoebae, with or without Xagella, and the other consisting of a
distinctive multinucleate structure, the plasmodium (Martin et al. 1983). Under favorable
conditions, the plasmodium gives rise to one or more fruiting bodies containing spores.
IdentiWcation of myxomycetes is based almost exclusively upon features of the fruiting
body (Martin and Alexopoulos 1969). The fruiting bodies produced by myxomycetes are
somewhat suggestive of those produced by higher fungi, although they are considerably
smaller (usually no more than 1–2 mm tall). The spores of the vast majority of myxomycetes
range in size from 5 to 15 �m in diameter, with most species producing spores 10 § 2 �m
in diameter. Presumably, the spores are wind-dispersed and complete the life cycle by
germinating to produce the uninucleate amoeboXagellate cells. These feed and divide by
binary Wssion to build up large populations in the various microhabitats in which these
organisms occur. Ultimately, this stage in the life cycle gives rise to the plasmodium. This
process can result from gametic fusion between compatible amoeboXagellates or it can be
apomictic (Collins 1980, 1981). Bacteria apparently represent the main food resource for
both trophic stages, but plasmodia are also known to feed upon yeasts, algae (including
cyanobacteria), and fungal spores and hyphae (Stephenson and Stempen 1994). Under
adverse conditions, such as drying out of the immediate environment or low temperatures,
a plasmodium may convert into a hardened, resistant structure called a sclerotium, which is
capable of reforming the plasmodium upon the return of favorable conditions. Moreover,
amoeboXagellate cells can undergo a reversible transformation to dormant structures called
microcysts. Both sclerotia and microcysts can remain viable for long periods of time and
are probably very important in the continued survival of myxomycetes in some ecological
situations and/or habitats, such as the bark surface of living trees and deserts.
The fruiting bodies of many species of myxomycetes can achieve macroscopic dimen-
sions and be collected and preserved for study in much the same way as the sporocarps of
Protist Diversity and Geographical Distribution 53
fungi or even specimens of bryophytes, lichens, and vascular plants. However, most
species of myxomycetes tend to be rather inconspicuous or sporadic in their occurrence and
are not always easy to detect in the Weld. Moreover, fruiting bodies of most species are
relatively ephemeral and do not persist in nature for very long. Myxomycetes also spend a
portion of their life cycle in a state where their very presence in a given habitat can be
exceedingly diYcult if not impossible to determine. Because of their life history strategy
and inconspicuous nature, these organisms provide an immense challenge in biodiversity
assessments and, consequently, often have been neglected in such studies.
Approximately 875 species of myxomycetes have been described (Lado 2001), and these
have been placed in six diVerent taxonomic orders (Ceratiomyxales, Echinosteliales,
Fig. 1 Life cycle of a typical myxomycete. A, Spore. B, Germinating spore. C, Uninucleate amoeboid stage,
with (right) or without (left) Xagella. D, Microcyst. E–F, Fusion of two compatible amoebae to produce a sin-
gle cell. G, Zygote. H, Early plasmodium. I, Sclerotium. J, Portion

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