Synopsis top ↑
The microscopical study of species of Scytinostroma in herbarium is
often difficult. Basidiospores, generative hyphae,gloeocystidia and
even basidia are often difficult to be found and consequently to be
correctly described and measured. Therefore we paid very much
attention to fresh or very recent collections which got.a spore print
or which were still sporulating. So it is possible to give accurate
measures of spores, to assert the reaction SA+ or SA- of
gloeocystidia, and the presence or the absence of
clamp—connections. Moreover we can also try to obtain monosporous
and polysporous cultures which supply very useful informations,such as
the confirming of he lack or the distribution of clamps and, of
course, the performing of intercompatibility tests if the species is
The collections studied in that way were chiefly originating from Europe, Africa (especially Gabon, but also Ivory Coast, Centrafrican Republic, Madagascar, Island of Reunion), central America (especially Guadeloupe and Martinique), South East Asia (Sri Lanka, Singapore, Bali).
Howewer this work is not exactly a world wide revision of the genus ScytLQOAtaama. Nevertheless we were braught to study specimens originating from very various countries (more particularly from Bourdot's, Burt 's, G.H.Cunningham's and Corner's herbaria) and determinations were confirmed or corrected whenever it was possible.
Technics: except where otherwise stated, basidiospores were measured and drawn in KOH 3%— Phloxine. Measures of fibers were made in Melzer. Moreover several means were used to disentangle fibers:
AMA or Ammonia—acetic Melzer: the sections were immersed, for 15 to 24 hours,in Ammonia at 60°C,then neutralized by acetic acid before being mounted in Melzer (or directly mounted in acetic Melzer).
AC 60: the sections were immersed for 15 to 24 hours in ammoniacal Congo Red at 60°C (or immersed in ammonia and then mounted in Congo Red).
The use of sulfuric aldehydes (abbreviated as SA) makes gloeocystidia easier to found. We.usually use the reactive "sulfo—anisic" which is prepared at the moment of the use by adding a little drop of aldehyde with a larger drop of 80% sulfuric-acid on a slide. Let us remind that the sequiterpen esters responsible for the reaction SA+ are very fragile and consequently a negative result is not significant when obtained with a rather old exsiccatum or even with a not alive collected specimen.
Two problems are difficult to solve: choose the name of genus and define its limit with the genus VaaaaLa Karst. Only temporary solutions will be given.
A— Choice of the legitimate name of the genus: is Stereofomes Rick (1928) priority synonym with Scytinostroma Donk (1956) ?
By mistake, W.B.Cooke (1953) chose S.resupinatus Rick as the type, - he taught Stereofomes had been created in 1931—. In 1959, B.Rambo repeated the same thing in the posthumous publication of Rick, dead 13 years before. In 1957, Donk chose S.nodulosus Rick as it was the best described Stereofomes in 1928. We could not locate the holotypes of these two species. S.resupinatus : The only collection mentionned in 1959 (number 15.246, from S.Leopoldo) was collected in 1930, two years after the creation of this species. It is whithout spores. S.nodulosus was collected in Sta Cruz (Porto Novo) according to the original diagnosis in 1928. In 1959 B.Rambo noticed 4 collections but no one is from Sta Cruz and only one is anterior to 1928 (number 19.590, Itapiranga 1926),not to be found at present. Nevertheless, in Lloyd's Herbarium (BPI), there is one specimen in good condition, originating from Sta Catharina, undated but together with a manuscript paper on which Rick noted :"Stereofomes nov.genus, Sterofomes nodulosus Rick, on palm" and overleaf: "I found this in Sta Catharina, on the wood of Chapico...very fine found." We describe this specimen (p.11 and fig.l p.12).At firts sight, it looks like a Fomes, its spherical amyloid spores are similar to those of C.portentosum, and its branched dichofibers can compared with dichophyses. This specimen cannot be ascertained identical to that from Sta Cruz and to that of Itapiranga, both of them are indiscoverable. So as far as we are not able to find again these two specimens and to study them, we leave the name of genus Sterofomes aside.
B— Limit between Scytinostroma and Vararia : Usually the genus Scytinostroma is characterized by dextrinoid fibers and the genus Vararia by dextrinoid dichophyses or dichohyphidia. Nevertheless a careful study shows that fibers exist in some Vararia and some dichophytical elements sometimes indisputable dichophyses are present in some chthOAIAQma Ac- tually the passage from single fibers to fibers with more or less dicho— tomic ramifications (or "dichofibers”), and even to true dichophyses can be sometimes observed in the same basidiocarp. If the species with sphe- rical amyloide spores are considered as closely related and born of a common and still close ancestor, then it must be admitted that, in the same phyllum,dextrinoid elements are going from single fibers of S.aluta, S. cystidiatum and S. duriusculm to those more branched of S.phaeosarcum, S. ahmadii and finally to those much more dichophytic of S.hemidichophyticum and particularly of S.albo-cinctum and of Stereofomes nodulosus. On the contrary, it can be considered that spherical amyloid spores appeared at one and the same time in a phyllum with single fibers and in a phyllum with dichofibers, and are only the result of a convergence. In the absence of paleontological answer and waiting for the measures of intervals between species (tests of in—vitro hybridization of their isolated DNA), we will not come to a decision.
Within the genus Scytinostroma, we keep the species with fibers and (or) with dichofibers which, on a section, show an inextricable network of dextrinoid fibers making the searching for the generative hyphae difficult. The generotype of the genus Scytinostroma chosen by Donk is Corticium portentosum Berk.& Curt., American species that Donk thaught well known and spread in Europe. Today, two species are recognized in Europe: S.hemidichophyticum Pouzar (supposed to be synonymous with S. portentosum by Hallenberg (1985) and S.aluta Lanquetin (1984). We asked for fresh collections of S.portentosum from Pennsylvania, the original country of the type of this species in orden to obtain monokaryotic cultures and to perform intercompatibility tests with S.hemidichophyticum, S.duriusculum and perhaps S.aluta, as well as the observation of gloeocystidia in sulfo—aldéhydes. At the present time, this project is still to be realized. If there still remains a doubt as to the species to be put in synonymy with C.portentosum, on the contrary all the mycologists agree to say the. se different species are indisputably congeneric. The conception and the definition of the genus Scytinostroma by Donk is without ambiguity. If necessary, to avoid unuseful changes in nomenclature, and in agreement with several colleagues, we will propose the genus Scytinostroma to be accepted as nomen conservandum.
In addition to Stereofomes nodulosus and Vararia alticola, 30 species of Scytinostroma are described, 13 species and one variety are proposed as new; moreover 6 insufficiently known species are temporarily described.
If we leave aside S.arachnoideum with its ornamented spores and S.rhizomorpharum Rattan with its loose texture, as their place is debatable in the genus Scytinostroma, then we can divide the other species into 4 groups:
Group 1- : Spores subglobose, amyloid and binucleate; hyphae without clamp connections; heterothallism:
S.aluta, duriusculum, cystidiatum, hemidichophyticum, ahmadii, corneri, albo-cinctum and Stereofomes nodulosus, P.D.D. 14.170 and Malaisie 1930. S.renisporum can be added in spite of a slightly different shape of spores. In this group, all types of fibers can be observed.
Group 2-: Small spores subglobose to shortly ellipsoid, not amyloid, sometimes with a "bavette"; hyphae clamped. In the cultivated species: spores uninucleate, nuclear behaviour "normal", bifactoriel heterothallism:
S.ultsp. galactinum, parvisporum, mivrospermum, pulverulentum, vernulosum and jacksonii.
Group 3-: Spores more elongated, but L/W = 2, binucleate, not amyloid; hyphae withoutclamps; nuclear behaviour "subnormal"; heterothallism:
S.ochroleucum, phaeosarcum, odoratum, Solomon Islands 8.373.
Group 4-: Spores fusiformes or in crescent, more than twice as long as wide. It can be divided into 2 subgroups:
Subgroup A: fiber with few ramifications:
S.praestans, luteolum and Atkinson 3.406 are clamped; S. Singapore 8.259 with very rare clamps in culture; S.decidens, mediterraneense without clamp-connections.
Subgroup B: fiber with racemose outgrowths:
S.intextum, crispulum and caudisporum all of three without clamp-connections and presumef homothallic.
Cultural characters are summarized (tabl. III, p.112). Many confrontations between monokaryotic cultures of.5. ultsp. galactinum have lead us to recognize 4 sibling species having a distinct geographical distribution (tabl.I,p.53, et tabl.II p.110).
A key into English is given below.
The importance of basidiospores is obvious as diagnostric character. So to any collector of Scytinostroma we highly recommend to obtain a spore-print for each specimen. We accept to study any recent collection provided with a spore-print.