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Remarks (public):The arid waxy, almost coriaceous, basidiocarps of Exidiopsis calcea, which often become pure white to light grayish white upon drying, are almost sufficiently characteristic to identify the species macroscopically. When moist the basidiocarps are only slightly duller than dried specimens. Microscopically the dimensions and morphology of the hymenial elements distinguish this species. Because of the intermediate forms, we suggest that the dikaryophyses and cystidioles designated for this species are only extremes of one type of sterile hymenial element. This may well be the case in several other species of Exidiopsis as well.
Exidiopsis calcea seems to be the most widely distributed and common species of the genus in the U.S.S.R. As Oberwinkler (1963) reported for southern Bavaria, in the northern zones east of the Ural Mountains, E. calcea is most frequently collected on Picea abies. In Siberia the species evidently
FIG. 5. Exidiopsis calcea. A-C. Segments of fertile hyphae (A from TAA 15314; B,C from TAA 6964). D. Basidium (TAA 69640 ). E,F. Dikaryophyses (TAA 16220 ). G-I. Cystidioles (G,H from TAA 16220; I from TAA 6964 ). J-L. Basidiospores. (J from TAA 12616; K from TAA 16220; L from TAA 6964 ).
occurs commonly on Larix gmelini and L. russica. Decaying Picea obovata is not an usual substrate in the northern regions both east and west of the Ural Mountains. In the Crimean Peninsula and in the vicinity of the Caucasus Mountains, E. calcea has been most commonly collected from decaying angiosperm wood.
While Christiansen (1959) did not report this species from Denmark, Wells (1962) determined M. P. Christiansen 609, which Christiansen had reported as Sebacina umbrina Rogers, as Exidiopsis macrospora (Ell. et Everh.) Wells. We now believe that this specimen, as well as the other specimens of E. macrospora cited by Wells (1962) from Europe, should best be labelled E. calcea.
Neuhoff (1936) and Eriksson (1958) noted that E. calcea was common on species of Picea in Sweden. Pilát (1957) found that E. calcea had been collected most frequently in Czechoslovakia and several neighboring countries, including the U.S.S.R., on decaying Picea abies, less frequently on other conifer species, and rarely on angiosperm wood. Malençon (1957) and Boidin and Lanquetin (1965) reported E. calcea from Morocco on angiosperm wood, and Boidin (1957a) noted that it was extremely common on Picea abies in the Haute-Savoie of France but was also found on angiosperm wood. In southern France (Haute-Garonne ), Boidin (1957b) recorded E. calcea on a species of Salix. Thus, while E. calcea seems to occur more commonly on decaying conifer wood, especially on Picea abies, it has also been reported from several regions on angiosperm wood.
An authentic specimen of Thelephora calcea Persoon from the Rijksherbarium in Leiden, Holland, was also examined. While the specimen is in poor condition, the observable features conform to the concept outlined above. Thus, as Boidin and Lanquetin (1965) suggested, the concepts of Wittlake (1938), McGuire (1941), Martin (1952), and Wells (1962) of Exidiopsis calcea were incorrect. Their descriptions were based on a species that is probably undescribed. Exidiopsis macrospora ( Ell. et Everh.) Wells [- Sebacina macrospora ( Ell. et Everh.) Burt, Eichleriella macrospora ( Ell. et Everh. ) Martin) as defined by Burt (1915 ), McGuire (1941), and Wells (1962) is very closely related, or possibly identical, to Exidiopsis calcea as we have defined it here. The basidiocarps of North American collections tend to form scattered tubercules, which are not evident in the specimens from the U.S.S.R. that we have examined. Since other features are nearly identical, we were tempted to consider Corticium macrosporum Ell. et Everh. as a later synonym of Thelephora calcea Pers.; however, we believe that mating experiments should be made between European and North American specimens before such changes are made.
 
Description type:Non-original description 
Description:Exidiopsis calcea (Pers.) Wells, Mycologia 53: 348. 1962. FIG. 5
Thelephora acerina var. abietis Fries, Syst. Mycol. 1: 453. 1821. Thelephora calcea Pers., Mycol. Eur. 1: 153. 1822.
Thelephora calcea c. albido-fuscescens Fries, Elench. Fung. 1: 215. 1828. Corticium calceum (Pers.) Fries, Epicr. Syst. Mycol., p. 562. 1838. Xeocarpus farinellus Karst., Bidrag Kännedon Finlands Natur Folk 37: 139. 1882.
Sebacina letendreana Pat., Rev. Mycol. (Paris) 7: 152. 1885.
Thelephora letendreana (Pat.) Sacc., Syll. Fung. 6: 541. 1888. Sebacina calcea (Pers.) Bres., Fungi Trid. 2: 64. 1892.
Corticium abietis (Fries) Romell, Bot. Not. 1895: 72. 1895.
Basidiocarps arid waxy to somewhat coriaceous, effused, pure white, grayish white to light ochraceous, arising as small porous reticulate to pruinose patches and becoming confluent to form extensive irregular basidiocarps; surface granulose to pruinose, irregular; margins thinning out to, rarely, abrupt, porous reticulate to fimbriate, lighter; drying lighter, chalky, grayish white to light buff, often cracking and exposing light subhymenium, strongly pruinose; in section (40-)45-250(-630) µm, consisting of a thin prostrate layer that is often absent, and an ascending layer of interwoven hyphae terminating in hymenium of fertile hyphae, dikaryophyses, and cystidioles, mineral granules often abundant in the subhymenium, the hymenium, or throughout, portions of the substrate often present in the ascending layer, pro- and hypobasidia formed in a well defined layer 25-50 µm wide and usually covered by a relative sparse but distinct layer of dikaryophyses and cystidioles 15-35 µm wide, growth strata rarely evident; subhymenial hyphae ( 1.5-)2-5.5(-6.5) µm in diam, hyaline, usually distinct, with clamps, tending to develop thickened walls in older portions; dikaryophyses simple to little branched, often nodulose apically, thin walled, hyaline, becoming indistinct in some specimens, 1-5( -8.5 ) µm in diam; cystidioles subcylindrical, subclavate, subfusiform, or irregular, hyaline, usually thin walled, becoming de- void of contents, rarely projecting, 23-75(-85) x (1-)2-10(-12) µm, hymenial elements intermediate in form between dikaryophyses and cystidioles common; fertile hyphae 2-5 ( -6) µm in diam; probasidia arising as cylindrical or narrow clavate proliferations through or near a sub-basidial clamp then becoming clavate to broadly fusiform or oval; hypobasidia with a basal clamp, forming (2- ) 4 hypobasidial segments, becoming oval, ovate, elliptical oblong, obovate to clavate, or, rarely, subglobose, also scarcely seen pyriform hypobasidia with enucleate stalks, (12- )14-18.5-25( -30) x (8- ) 9.5-12.5-15(-16) µm, becoming guttulate at maturity; epibasidia tubular, often flexuous, although somewhat irregular usually equal in diam throughout, (2.5-)3-4(-4.5)µm in diam, up to 58 µm in length; basidiospores allantoid to cylindrical curved, sometimes approaching helicoid, often guttulate, (10.5-)12-15.5-18(-19) x (4-)5-7(-7.5) µm, capable of germinating by repetition.
On decaying conifer and, less often, angiosperm wood. Known from Germany, Czechoslovakia, Holland, Sweden, France.
Illustration. - Oberwinkler, F. 1963. Ber. Bayer. Bot. Ges. 36: 51, Fig. 19. Type locality. - Europe.
 
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