179 Mycoscience 35: 179-181, 1994 Ap/opsora corni sp. nov. on Comus controversa from Hokkaido, Japan Yoshitaka Ono 1) and Yukio Harada 21 ~) Faculty of Education, Ibaraki University, 2-1-1 Bunkyo, Mito, lbaraki 305, Japan 21Faculty of Agriculture, Hirosaki University, 3 Bunkyo-cho, Hirosaki, Aomori 036, Japan Accepted for publication 28 March 1994 Aplopsora cornisp, nov. is proposed for a rust fungus whose uredinial and basidial stage occurs on Comus controversa (Cornaceae) in Hokkaido. This new species is separated by its larger urediniospores and probasidia from the mor- phologically closely related A. nyssae on Nyssa aquatica and IV. sylvatica (Cornaceae) distributed in southern North America. Key Words Aplopsora; Chaconiaceae; Cornaceae; Comus; Uredinales. A rust fungus was found by the junior author on Comus controversa Hemsley at Shizunai, Hokkaido in September 1991. Old uredinia and basidiosori were formed on adax- ial surface of the leaves. The uredinia were minute, brownish, and scattered or in a small group on reddish brown lesions; and the basidiosori were minute, whitish, and loosely or densely aggregate on slightly discolored and diffused lesions. The uredinia (Fig. 1) were subepidermal, becoming exposed and surrounded by paraphyses at the periphe- ry. The paraphyses (Fig. 1) were cylindric, up to 60 pm long, not or weakly inflated and often incurved at the dis- tal end and united at the base. The wall was evenly 2- 3 pm thick or slightly thickened at the distal end and yel- lowish brown. The urediniospores (Figs. 1, 2) seemed to be formed directly from the sporogenous cells, not being intercalated by a pedicel cell. Because the sori were old and almost collapsed, however, no detailed ex- amination to determine the exact mode of urediniosporo- genesis was possible. The spores were broadly ellipsoid or obovoid-eltipsoid and (22-)25-30x 18-24#m in size. The wall was evenly 1-1.5/~m thick, light cinna- mon-brown and completely echinulated. Six germ pores were scattered over the wall. The basidiosori (Fig. 3) were subepidermal, becom- ing exposed by developing pro- and metabasidia from the underlying hymenium and often appeared cinereous or tomentose due to abundantly developed metabasidia and basidiospores. Neither paraphysis nor peridium was present in the sori. The probasidia (Fig. 3) were one- celled, formed in one-layer, laterally free, oblong or cylin- dric, 43-68x 15-24pm in size, thin-walled and color- less. The probasidia were laterally free, but firmly at- tached on the hymenium. No meristematic cells that gave rise to the probasidia were apparent in the hymeni- urn, The seemingly young sori appeared as a whitish waxy crust and mature ones tomentose with continuous gradation between these as observed on the specimen in- dicated that the probasidium developed into the metabasidium by continuous apical elongation. The metabasidia (Figs. 4 and 5) were four-celled, cylindric, slightly curved and 58-75 × 14-22 #m in size (excluding subtending and collapsed probasidiat portions). The apex of the metabasidiat spicuta were often rounded (Fig. 5) as opposed to the acute-pointed ones usually observed in many basidiomycetous fungi. The basidiospores (Fig. 6) were obovoid or obovoid-ellipsoid and 19-24x 16- 20 #m in size. The pro- and metabasidial characteristics suggest that this fungus is taxonomically closely related to such genera of the Chaconiaceae (Cummins and Hiratsuka, 1983) as Aplopsora, Ceraceopsora, Chaconia, Chrysoce- lis, Goplana, Ochropsora and Ofivea, whose probasidium does not possess a pedicel. Not all species of these rust genera are known over their complete life cycle or with regard to the structural characteristics of the sori at each stage. Combination of currently available, even though fragmental, structural-morphological characteristics of the sori and the spores at respective life-cycle stages cir- cumscribe and separate these genera (Cummins and Hiratsuka, 1983; Kakishima et al., 1984; Ono and Hen- nen, 1983; Ono, 1984). Thus, this common taxonomic practice causes seri- ous difficulty in classification and identification of a fun- gus whose life cycle and associated sori and spores are in- completely known. In order to over come this difficulty, assumed taxonomic importance is placed on 1) presence or absence of meristematic basal cells which give rise to probasidia, 2) external or internal formation of metabasidia (namely, whether the metabasidium forms by apical extension of the probasidium or replaces the probasidim without any appreciable morphological change), and 3) gelatinous nature of the basidiat sori. These characteristics are subsidiary to the "major" taxo-