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Page number:1168 
Remarks (public):T. mollusca grows on both coniferous and deciduous wood but in S weden only 7 out of 47 collections were from coniferous wood. Seven specimens grew on dead basidiomata of Fomes fomentarius or Phellinus igniarius. T. mollusca seem to prefer areas and localities with a high proportion of deciduous trees like Oland, the surroundings of Malaren, the inner part of Oslofjorden, Aland and the alpine birch-forest. Many collections stem from localities with a favourable climate and a rich, from the surroundings deviating flora.
T. mollusca is widespread in the Northern Hemisphaere. Its distribution in the Nordic countries shows an eastern-continental tendency. The lack of finds from nemoral areas, notably Denmark and Scania in southernmost Sweden is remarkable. Sjaelland, the surroundings of Göteborg and the Stockholm-Uppsala region are three areas where intense collecting have been undertaken. No fords on Sjaelland and 3 finds from Göteborg contrasts with 27 finds from Stockholm-Uppsala. These figures most likely reflects a true distribution. The northernmost parts of Sweden, Norway and Finland are poorly investigated. The 7 finds from this part indicates that T. mollusca is not uncommon in this area.
A high proportion of known finds date from before 1950 e.g. 26 of 27 finds from Stockholm-Uppsala. The possibility cannot be excluded that T. mollusca is showing a decline resulting from changes in habitat or air pollution.
The interpretation of Persoon's species has caused a lot of confusion. The current use of the name dates back to Donk (1967) who thoroughly discussed the problem. Persoon introduced Boletus molluscus for a resupinate, whitish, poroid fungus with a thin, soft, basidiome and small, unequal, somewhat lacerate pores. He had found it to be rare and growing on decayed coniferous wood. Following a beta-sign and a question mark he also listed the epithet epiphylla. This name was earlier introduced as Poria epiphylla (Persoon, 1799) and Persoon regarded it as rare and growing on deciduous wood. He seems to have known it only from the type locality and apparently felt uneasy about its status. In Mycologia Europaea (Persoon, 1825) it is definitely reduced to varietal status together with a new variety fcssus. There is no material in Persoon's herbarium named epiphylla. Boletus molluscus var fcssus is, according to Donk, the same as Antrodiella romellii (Donk) Niemela. Fries (1821) accepted the epithet mollusca as Polyporus molluscus while Poria epiphylla was mentioned as a synonym of a form b. tenuissimus. The epithet tenuissimus can not be connected with an authentic specimen.
The use of Persoon's name seem to have followed the original meaning until Bresadola (1897) gave it a different interpretation. Bresadola used the name mollusca for a smooth-spored species now called Porpomyces mucidus (Pers.:Fr.) Rilich (syn. Fibuloporia donkii Dom., Fibuloporia mucida (Pers.: Fr.) Niemelä) another Persoonname. For the species here dealt with, with ornamented spores, Bresadola reintroduced Boletus subtilis Schrader. This interpretation was followed by Bourdot & Galzin (1928) and gained wide acceptance concerning the use of mollusca but not the use of subtilis (Donk,1933; Romell, 1911).
In the herbarium of Persoon there are several specimens named Boletus molluscus, often accompanied on the packet by other names and interrogation marks. One of these collections was already by Lloyd and by Bresadola suggested as type according to notes on the packet (Lloyd: 'This is the type';
Bresadola: 'Typus! sed non = Poria subtilis (Schr.)Bres ut vult Romell'. See below!). Donk (1933) also pointed out this specimen as type ('...das ich für den Typus halte... `) but preferred to name his material Poria candidissima (Schw.)Sacc. (incorrect author) because of the confusion associated with the epithet mollusca.
Following the tradition of Bresadola, Lowe (1966) choose a neotype (incorrectly called lectotype) from the Bresadola material at herb S (Eichler No. 38). Donk (1967) changed his mind about what name should be used. He had now been convinced that mollusca could be clearly defined with the material in Persoon's herbarium and he once again pointed out the specimen earlier discussed as a type. He rejected Lowe's action as illegitimate according to the Code (misapplied name) and argued that Lowe did not pay regard to the existing herbarium material. Donk considered the specimen he selected as a lectotype. All later authors have followed Donk.
There is nothing on the packet in Persoon's specimen that indicates Persoon saw it before the name was published. Furthermore, at the date of publication Persoon apparently new the species only from coniferous wood ('incolit ligna exsiccata pinea'). An examination of the presumed lectotype shows it to grow on deciduous wood. The typification by Donk thus must be regarded as selection of a neotype. This gives us two neotypes, the one selected by Lowe having priority unless its selection can be shown to have violated the Code.
Lowe followed a tradition from Bresadola and by his typifrcation he contributed to stability in naming. We do not know on what material Bresadola based his opinion. He could very well have seen other material from Persoon's hand than any of the collections now left in his herbarium. Bresadola obviously saw the collection which Donk selected as neotype and he agreed it was a type ('Typus!'). However this notation was apperantly done long after he first published his opinion in 1897 because he was able to quote Romell as having conunitted an error in regarding Poria subtilis as a synonym (see above). Romell did not publish this opinion until 1911 (Romell, 1911). One can easily understand Bresadola's mistake about the true nature of the supposed type considering that he already had a firm opinion about Persoons species and therefore at the occasion he made his note, maybe it was not examined under the microscope and, secondly, because this specimen in outer appearance looks very much like Poria mollu
sca sensu Bresadola and rather different from typical Poria subtilis sensu Bresadola.
At the time Donk made his typifrcation it could have been seriously questioned. Today, when Donk,s opinion has been accepted for more than 20 years, nothing will be gained by once again changing names. Besides there are several collections from Persoon's hand being mollusca but today no collection so named that conforms with Bresadolas interpretation.
Fries knew the species under discussion well and regarded it as common ('frequens` Fries, 1863). There is no material left which could be used for a lectotypification but there are collections in Kew and in Edinburgh with Fries' handwriting and of different identity. A collection in Edinburgh shows T. hymenocystis. Ryvarden & Johansen (1980) held this specimen for a type. However, its status would be that of a neotype since no Friesian material of a sanctioned name can be regarded as holotype or lectotype. Such material can only be found with the original author. As two neotypes were already chosen before 1980 the Edinburgh collection has no special interest for typication. The International Code of Botanical Nomenclature does not permit a change of neotype in a case like this.
Lowe (1966) lists Polyporus gordoniensis Berk. & Br. (1865) as a synonym with T, mollusca. The identity was confirmed by Reid & Austwick (1963). They noted that there was three collections in Kew bearing the epithet gordoniensis, two from the type locality and being identical, and one sterile collection from Strachan, Kincardineshire. The two collections from Aboyne Castle are probably the original type which has been divided. The Aboyne Castle collection shows a typical resupinate polypore with a dimitic, or a thick-walled, monomitic, hyphal system and belonging in Antrodia or Tyromyces. The,,. material is lacking sterile elements and neither basidia nor spores could be located.
T. mollusca has several distinctive characters. The basidiomata usually have an adnate growth habit and often an abrupt margin. Pore diameter varies a lot depending on growth conditions and age but are rather small, at least when compared with other poroid Trechispora species. However, the figures for pore diameter given here will be seen only when basidiomata are growing on a smooth substrate in a perfectly downward position. The whitish colour, which only fades slightly in the herbarium, is striking when compared with T. hymenocystis. T. mollusca
usually has a poorly developed subiculum and cords are not prominent. Crystals are common throughout and consists of rosette-like druses or just a grainy mass. The hyphae are of a uniform width, rather narrow and have somewhat thickened walls. Spores are subglobose with a tendency to have the dorsal side flat and they are laterally compressed. Aculei are small and densely arranged. T. mollusca seem to accept living in more exposed places than T. hymenocystis and T. candidissima.
 
Description type:Non-original description 
Description:Trechispora mollusca (Pers.:Fr.) Liberta (Figs 9-10, 26-27, 30, 37-38) Can. J. Bot. 51:1878 (1973).
Neotype (designated by Donk 1967). Herb. Persoon, L 910.270-437 (L).
Boletus molluscus Pers., Syn. Fung. p. 547 (1801). Polyporus molluscus Pers.:Fr., Syst. mycol. I p. 384 (1821). Basidiomata resupinate, effused, soft and fragile, easily separable from the substratum. Margin thinning out, sharply delimited towards the substratum or with white, sterile hyphal mats, sometimes forming cord-like structures. Hymenophore poroid, pores shallow and up to 1 mm deep, rounded to irregular but not angular, 2.5-5/mm, dissepiments thin, slightly fringed from emergent hyphae, whitish to light ochraceous or straw-coloured. Hyphal system monomitic, all hyphae with clamps. Cords with straight, uniform, slightly thick-walled, 1.5-2.5 µm wide hyphae, some of them appearing rough from swellings and protuberances on the outer cell-wall, with numerous ampullate septa up to 6 µm wide. Subiculum forming a thin layer consisting of straight, moderately branched, often anastomosing, slightly thick-walled and 2-3 µm wide hyphae, frequently with the same kind of roughness but also with crystalline matter, either in druses or as small, single crystals. Dissepiments with thin-walled, 2-3 µm wide, mainly straight hyphae, also with both roughening and incrustation. Subhymenium forming a thin, often only one-cell thick layer of thin-walled, short-celled hyphae with rounded or irregular outline, 2-4 µm wide, branching of at right angles from the tramal hyphae, often lacking altogether. Basidia cylindrical to doliform or with a slight median constriction, often with aberrant forms due to the different growth conditions provided on the dissepiments and hence often seen as pleurobasidia, mainly measuring 10-14 x 5 µm, with four curved, slender, 4-5 µm long sterigmata. Spores densely aculeate, subglobose, with the adaxial side slightly flattened, 3.5-4 x 3-3.5 µm as seen in side-view and including the 0.3 µm long spines, somewhat compressed and hence slightly narrower as seen in dorsal view, not or only weakly cyanophilous. Crystals formed as aggregated bipyramids.
 
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