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organisms in vivo. It is also possible that some researchers have noted fungi occurring with their algae fossils, but did not bother to address them because they were
merely interested in the algae and/or lacked the expertise to adequately describe
fungal remains.
Perhaps the best fossils of fungal parasites of algae come from the Lower
Devonian Rhynie chert, together with the earliest evidence of hypertrophy (i.e.
increase in cell size as a result of an external stimulus) in the fossil record. Chytridlike organisms are common parasites of the Rhynie chert charophyte Palaeonitella
cranii (Taylor et al. 1992b, c). One of these organisms, Milleromyces rhyniensis, is
characterized by an endobiotic zoosporangium extending out from the charophyte
cell wall (Fig. 3.3l). At the base of the zoosporangium is a rhizoidal system. Other
chytrid-like organisms associated with P. cranii include Lyonomyces pyriformis and
Krispiromyces discoides, which differ from one another in thallus morphology.
Both M. rhyniensis and K. discoides are associated with hypertrophic host cells
(Fig. 3.3m), which grow to approximately five times the diameter of normal cells
(Fig. 3.3n), and thus prove that colonization occurred while the host was alive. This
same pattern in cell increase in response to chytrid parasitism has been reported in
the modern genus Chara (Karling 1928), a distant relative of P. cranii.
3.3.3 Fungal Parasites of Other Fungi
The term mycoparasitism is used to describe the interfungal interrelationships of a
fungus parasite and a fungus host (Barnett 1963; Jeffries and Young 1994). There
are numerous examples of mycoparasitism in the fossil record, the majority of
which come from the Lower Devonian Rhynie chert.
3.3.3.1 Rhynie Chert Interfungal Interactions
Rhynie chert evidence of interfungal associations ranges from fungal mycelia and
reproductive units in the lumen of other fungal reproductive units (Kidston and Lang
1921; Krings et al. 2009a, 2010a, 2015, 2016), to fungal hyphae enveloping and subsequently penetrating fungal vesicles (Krings and Taylor 2014b), to fungal reproductive units developing in glomeromycotan vesicles (Fig. 3.4a) (Harper et al. 2017b).
Moreover, numerous monocentric and polycentric chytrid-like organisms have been
described as intruders of fungal hyphae and spores. Most of these organisms consist
of epibiotic sporangia and rhizoidal systems extending into the host spore lumen
(Fig. 3.4b) (Taylor et al. 1992a; Krings and Taylor 2014a; Krings and Harper 2019).
Other chytrid-like intruders of fungal spores are found between particular wall layers
of fungal spores or occupying the spore lumen (Hass et al. 1994). Unfortunately, the
majority of fungi associated with other fungi in the Rhynie chert cannot be identified
C. J. Harper and M. Krings
organisms in vivo. It is also possible that some researchers have noted fungi occurring with their algae fossils, but did not bother to address them because they were
merely interested in the algae and/or lacked the expertise to adequately describe
fungal remains.
Perhaps the best fossils of fungal parasites of algae come from the Lower
Devonian Rhynie chert, together with the earliest evidence of hypertrophy (i.e.
increase in cell size as a result of an external stimulus) in the fossil record. Chytridlike organisms are common parasites of the Rhynie chert charophyte Palaeonitella
cranii (Taylor et al. 1992b, c). One of these organisms, Milleromyces rhyniensis, is
characterized by an endobiotic zoosporangium extending out from the charophyte
cell wall (Fig. 3.3l). At the base of the zoosporangium is a rhizoidal system. Other
chytrid-like organisms associated with P. cranii include Lyonomyces pyriformis and
Krispiromyces discoides, which differ from one another in thallus morphology.
Both M. rhyniensis and K. discoides are associated with hypertrophic host cells
(Fig. 3.3m), which grow to approximately five times the diameter of normal cells
(Fig. 3.3n), and thus prove that colonization occurred while the host was alive. This
same pattern in cell increase in response to chytrid parasitism has been reported in
the modern genus Chara (Karling 1928), a distant relative of P. cranii.
3.3.3 Fungal Parasites of Other Fungi
The term mycoparasitism is used to describe the interfungal interrelationships of a
fungus parasite and a fungus host (Barnett 1963; Jeffries and Young 1994). There
are numerous examples of mycoparasitism in the fossil record, the majority of
which come from the Lower Devonian Rhynie chert.
3.3.3.1 Rhynie Chert Interfungal Interactions
Rhynie chert evidence of interfungal associations ranges from fungal mycelia and
reproductive units in the lumen of other fungal reproductive units (Kidston and Lang
1921; Krings et al. 2009a, 2010a, 2015, 2016), to fungal hyphae enveloping and subsequently penetrating fungal vesicles (Krings and Taylor 2014b), to fungal reproductive units developing in glomeromycotan vesicles (Fig. 3.4a) (Harper et al. 2017b).
Moreover, numerous monocentric and polycentric chytrid-like organisms have been
described as intruders of fungal hyphae and spores. Most of these organisms consist
of epibiotic sporangia and rhizoidal systems extending into the host spore lumen
(Fig. 3.4b) (Taylor et al. 1992a; Krings and Taylor 2014a; Krings and Harper 2019).
Other chytrid-like intruders of fungal spores are found between particular wall layers
of fungal spores or occupying the spore lumen (Hass et al. 1994). Unfortunately, the
majority of fungi associated with other fungi in the Rhynie chert cannot be identified
C. J. Harper and M. Krings