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A key to British Exidia species
Field Mycology Volume 2(4), October 2001
A KEY TO BRITISH €X/D/A SPECIES Peter Roberts The Herbarium, Royal Botanic Gardens, Kew, Surrey TW9 3AE [email protected]
M
ost of the larger British heterobasidiomycetes produce gelatinous fruitbodies which are reasonably easy to identify in the field. The trick is to look upwards from time to time, instead of keeping your eyes on the ground. Gelatinization is one of several desiccation-defying strategies employed by fungi growing on exposed wood. The fruitbodies store water which helps maintain a damp microclimate for sporulation after rain stops and branches begin to dry. Accordingly, many gelatinous species only grow on dead attached twigs and branches, gradually giving way to less specialized species when the wood eventually falls to ground. Most of the larger British species belong to one of three genera: Auricularia, Exidia, or Tremella. Of these, Auricularia is usually easy to recognize since we have just two species: A . auricula-judae, the familiar “Jew’s ear fungus”, and A. mesenterica, the equally familiar “tripe fungus”. Tremella species are less easy, though in Britain we have only a few that are large and these are reasonably straightfoxward. They include the two bright yellow species, T aurantia (on Stereum hirsutum fruitbodies) and 7: mesenterica (on Peniophora mycelium), the brown to black, foliose T foliacea (on Stereum mycelium), and the pinkish, brain-like I: encephala (on Stereum sanguinolentum fruitbodies). Descriptions and colour photographs can be found in Roberts (1995,1999). This leaves Exidia. Unlike Tremella (a genus of parasites on other fungi), Exidia is a genus of wood-rotters, with just seven species so far recorded in the British Isles. They are readily distinguished microscopically by their allantoid (sausage-shaped) basidiospores, a spore shape never found in Tremella. Macroscopically, it is probably easiest to recognize each species individually.The following key may help.
1. Fruitbodies hyaline to whitish, occasionally tinted pink to violaceous . . . . . . . . . . . . . . .2 1. Fruitbodies distinctly coloured, orange, .3 brown, or black.. .................... 2. Mature fruitbodies whitish; effused, becoming plicate; no mineral inclusions; basidia not stalked. . . . . . . Exidia thuretiana 2. Mature fruitbodies hyaline to whitish, occasionally tinted pink to violaceous; pustular and coalescing; white mineral inclusions often visible; basidia distinctly stalked . . . . . . . . . . . . . . . . . .Exidia nucleata 3. Fruitbodies blackish-brown to black; hymenium with scattered warts or papillae 4 under lens .......................... 3 . Fruitbodies orange to brown; hymenium 5 smooth ............................. 4. Fruitbodies turbinate (top-shaped), often remaining separate, occasionally coalescing; typically on oak or hazel. . . Exidia glandulosa 4 . Fruitbodies effused, irregularly lobed, coalescing; typically on beech, willow, sycamore and other deciduous trees (but rarely, if ever, on oak) . . . . . . . . Exidia plana sensu Donk (1966) 5 . Fruitbodies brown, irregularly lobed; on pine . . . . . . . . . . . . . . . . . . Exidia saccharina 5. Fruitbodies orange to orange-brown; on .6 deciduous trees ..................... 6. Fruitbodies button-shaped; typically on birch. . . . . . . . . . . . . . . . . . . .Exidia repanda 6. Fruitbodies turbinate (top-shaped), often pendulous; typically on willow . Exidia recisa
Exidia thuretiana and E. nucleata are both common on deciduous wood and well-developed specimens are normally recognizable in the field. The former often grows along the underside of dead attached branches, the edges of the fruitbodies neatly
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Field Mycology Volume 2(4), October 2001 pleated, whilst the latter is irregularly pustular, with conspicuous white kernels of mineral matter visible under the surface. Young or small specimens, however, need microscopic examination to separate them from each other and from the similar, pustular species Tremella globispora. Exidia nucleata is commonly referred to the genus Myxarium and may not be closely related to other Exidia species (Weiss & Obenvinkler, 2001). Specimens tinted pinkish or violaceous are sometimes found and might be confused with similarly coloured gelatinous ascomycetes (Ascocoryne and Ascotremella species). If you examine Exidia nucleata microscopically, you may discover the auricularioid parasite Zygogloea gemelliparu, known from a very few English collections. Exidia glandulosa and “E.plana” are microscopically indistinguishable, but appear distinct in the field. Recent molecular research (Weiss & Obenvinkler, 2001) suggests they are indeed separate species. Their names are extraordinarily muddled and several pages could be taken up in arguing the case for using one dubious old epithet instead of another. But as treated here, E. glandulosa is the common, turbinate species often called E. truncata and most frequently found on oak (Quercus)or hazel (Corylus),whilst E. plana sensu Donk (1966)* is the rather less common, lobed, effused species usually found on deciduous trees other than oak. If you come across specimens of E. glandulosa covered in gall-like pustules, they may be parasitized by another heterobasidiomycete, Heteromycophaga glandulosae, known from several English collections. Be aware that the ascomycete Bulgaria inquinans bears a superficial resemblance to E. glandulosa, but is usually much more compact, lacks warts, and produces a black spore print. Exidia saccharina is the only British Exidia species on conifers (Pinus) and as such should be easy to recognize. It is mainly known from Scotland (collections from six sites at Kew), with just a single recent record from England (Devon). Surely it must occur somewhere in between, especially since it seems happy to colonize plantation pines? Exidia recisa and E. repanda form another microscopically indistinguishable pair. The former is widespread but local on dead attached twigs of willow (Salix),whilst the latter is mostly confined to twigs of birch (Betula) in Scotland (collections from five sites at Kew), with a single recent record
on hazel from Northern Ireland. Exidia recisa tends to be pendulous and turbinate, whilst E. repanda is button-shaped and more closely attached to the wood. Both can occasionally occur on poplar (Populus) and other deciduous trees. Not yet recorded from Britain, but worth looking out for, is the tiny discomycete, Gelatinopsis exidiophila, on old, decaying fruitbodies of Exidia recisa. Other Exidia species are found in continental Europe and might possibly turn up in the British Isles. Exidia pithya forms rather featureless, rubbery, tar-like patches on spruce (Picea) and should be quite easy to distinguish. Exidia cartilaginea resembles E. nucleata, but is typically bicoloured (brownish at centre, hyaline to whitish at the edges) and lacks stalked basidia. It is quite common on birch in Scandinavia and might be looked for in Scotland. Exidia umbrinella superficially resembles E. repanda, but occurs on conifers, mainly in southern Europe. Should you find any of these, or other interesting specimens, I shall be happy to examine them and add them to the national collections at Kew.
References Donk, M.A. (1966). Checklist of European hymenomycetous heterobasidiae. Persoonia 4: 145 - 335 Roberts, P. (1995). British Tremella species I: Eemella aurantia & T mesenterica. Mycologist 9: 110- 114 Roberts, P. (1999). British Tremella species 11. Tremella encephala, T steidleri, T foliacea. Mycologist 13: 127 - 131 Weiss, M. & Obenvinkler, F. (2001). Phylogenetic relationships in Auriculariales and related group? -hypotheses derived from nuclear ribosomal DNA sequences. Mycol. Res. 105: 403 - 415
* Exidia plana Wigg. was originally
described as green when young (“initio viridis” - Wiggers, quoted in Donk, 1966) which makes it sound more algal than fungal. Donk tried to resurrect the name, but it deserves reburial. Exidia applanata Schwein. may be the oldest applicable name for the species, but this nomenclatural confusion still needs sorting out.
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A KEY TO BRITISH €X/D/A SPECIES Peter Roberts The Herbarium, Royal Botanic Gardens, Kew, Surrey TW9 3AE [email protected]
M
ost of the larger British heterobasidiomycetes produce gelatinous fruitbodies which are reasonably easy to identify in the field. The trick is to look upwards from time to time, instead of keeping your eyes on the ground. Gelatinization is one of several desiccation-defying strategies employed by fungi growing on exposed wood. The fruitbodies store water which helps maintain a damp microclimate for sporulation after rain stops and branches begin to dry. Accordingly, many gelatinous species only grow on dead attached twigs and branches, gradually giving way to less specialized species when the wood eventually falls to ground. Most of the larger British species belong to one of three genera: Auricularia, Exidia, or Tremella. Of these, Auricularia is usually easy to recognize since we have just two species: A . auricula-judae, the familiar “Jew’s ear fungus”, and A. mesenterica, the equally familiar “tripe fungus”. Tremella species are less easy, though in Britain we have only a few that are large and these are reasonably straightfoxward. They include the two bright yellow species, T aurantia (on Stereum hirsutum fruitbodies) and 7: mesenterica (on Peniophora mycelium), the brown to black, foliose T foliacea (on Stereum mycelium), and the pinkish, brain-like I: encephala (on Stereum sanguinolentum fruitbodies). Descriptions and colour photographs can be found in Roberts (1995,1999). This leaves Exidia. Unlike Tremella (a genus of parasites on other fungi), Exidia is a genus of wood-rotters, with just seven species so far recorded in the British Isles. They are readily distinguished microscopically by their allantoid (sausage-shaped) basidiospores, a spore shape never found in Tremella. Macroscopically, it is probably easiest to recognize each species individually.The following key may help.
1. Fruitbodies hyaline to whitish, occasionally tinted pink to violaceous . . . . . . . . . . . . . . .2 1. Fruitbodies distinctly coloured, orange, .3 brown, or black.. .................... 2. Mature fruitbodies whitish; effused, becoming plicate; no mineral inclusions; basidia not stalked. . . . . . . Exidia thuretiana 2. Mature fruitbodies hyaline to whitish, occasionally tinted pink to violaceous; pustular and coalescing; white mineral inclusions often visible; basidia distinctly stalked . . . . . . . . . . . . . . . . . .Exidia nucleata 3. Fruitbodies blackish-brown to black; hymenium with scattered warts or papillae 4 under lens .......................... 3 . Fruitbodies orange to brown; hymenium 5 smooth ............................. 4. Fruitbodies turbinate (top-shaped), often remaining separate, occasionally coalescing; typically on oak or hazel. . . Exidia glandulosa 4 . Fruitbodies effused, irregularly lobed, coalescing; typically on beech, willow, sycamore and other deciduous trees (but rarely, if ever, on oak) . . . . . . . . Exidia plana sensu Donk (1966) 5 . Fruitbodies brown, irregularly lobed; on pine . . . . . . . . . . . . . . . . . . Exidia saccharina 5. Fruitbodies orange to orange-brown; on .6 deciduous trees ..................... 6. Fruitbodies button-shaped; typically on birch. . . . . . . . . . . . . . . . . . . .Exidia repanda 6. Fruitbodies turbinate (top-shaped), often pendulous; typically on willow . Exidia recisa
Exidia thuretiana and E. nucleata are both common on deciduous wood and well-developed specimens are normally recognizable in the field. The former often grows along the underside of dead attached branches, the edges of the fruitbodies neatly
134
Field Mycology Volume 2(4), October 2001 pleated, whilst the latter is irregularly pustular, with conspicuous white kernels of mineral matter visible under the surface. Young or small specimens, however, need microscopic examination to separate them from each other and from the similar, pustular species Tremella globispora. Exidia nucleata is commonly referred to the genus Myxarium and may not be closely related to other Exidia species (Weiss & Obenvinkler, 2001). Specimens tinted pinkish or violaceous are sometimes found and might be confused with similarly coloured gelatinous ascomycetes (Ascocoryne and Ascotremella species). If you examine Exidia nucleata microscopically, you may discover the auricularioid parasite Zygogloea gemelliparu, known from a very few English collections. Exidia glandulosa and “E.plana” are microscopically indistinguishable, but appear distinct in the field. Recent molecular research (Weiss & Obenvinkler, 2001) suggests they are indeed separate species. Their names are extraordinarily muddled and several pages could be taken up in arguing the case for using one dubious old epithet instead of another. But as treated here, E. glandulosa is the common, turbinate species often called E. truncata and most frequently found on oak (Quercus)or hazel (Corylus),whilst E. plana sensu Donk (1966)* is the rather less common, lobed, effused species usually found on deciduous trees other than oak. If you come across specimens of E. glandulosa covered in gall-like pustules, they may be parasitized by another heterobasidiomycete, Heteromycophaga glandulosae, known from several English collections. Be aware that the ascomycete Bulgaria inquinans bears a superficial resemblance to E. glandulosa, but is usually much more compact, lacks warts, and produces a black spore print. Exidia saccharina is the only British Exidia species on conifers (Pinus) and as such should be easy to recognize. It is mainly known from Scotland (collections from six sites at Kew), with just a single recent record from England (Devon). Surely it must occur somewhere in between, especially since it seems happy to colonize plantation pines? Exidia recisa and E. repanda form another microscopically indistinguishable pair. The former is widespread but local on dead attached twigs of willow (Salix),whilst the latter is mostly confined to twigs of birch (Betula) in Scotland (collections from five sites at Kew), with a single recent record
on hazel from Northern Ireland. Exidia recisa tends to be pendulous and turbinate, whilst E. repanda is button-shaped and more closely attached to the wood. Both can occasionally occur on poplar (Populus) and other deciduous trees. Not yet recorded from Britain, but worth looking out for, is the tiny discomycete, Gelatinopsis exidiophila, on old, decaying fruitbodies of Exidia recisa. Other Exidia species are found in continental Europe and might possibly turn up in the British Isles. Exidia pithya forms rather featureless, rubbery, tar-like patches on spruce (Picea) and should be quite easy to distinguish. Exidia cartilaginea resembles E. nucleata, but is typically bicoloured (brownish at centre, hyaline to whitish at the edges) and lacks stalked basidia. It is quite common on birch in Scandinavia and might be looked for in Scotland. Exidia umbrinella superficially resembles E. repanda, but occurs on conifers, mainly in southern Europe. Should you find any of these, or other interesting specimens, I shall be happy to examine them and add them to the national collections at Kew.
References Donk, M.A. (1966). Checklist of European hymenomycetous heterobasidiae. Persoonia 4: 145 - 335 Roberts, P. (1995). British Tremella species I: Eemella aurantia & T mesenterica. Mycologist 9: 110- 114 Roberts, P. (1999). British Tremella species 11. Tremella encephala, T steidleri, T foliacea. Mycologist 13: 127 - 131 Weiss, M. & Obenvinkler, F. (2001). Phylogenetic relationships in Auriculariales and related group? -hypotheses derived from nuclear ribosomal DNA sequences. Mycol. Res. 105: 403 - 415
* Exidia plana Wigg. was originally
described as green when young (“initio viridis” - Wiggers, quoted in Donk, 1966) which makes it sound more algal than fungal. Donk tried to resurrect the name, but it deserves reburial. Exidia applanata Schwein. may be the oldest applicable name for the species, but this nomenclatural confusion still needs sorting out.
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