Diderma subochraceum Shuang L. Chen et Yang Gao, 2018

Gao, Yang, Yan, Shu-Zhen, Wang, Gao-Wei & Chen, Shuang-Lin, 2018, Two new species and two new records of myxomycetes from subtropical forests in China, Phytotaxa 350 (1), pp. 51-63 : 55-57

Diderma subochraceum Shuang L. Chen et Yang Gao , sp. nov. FIGURE 2 .

MycoBank: MB 823955

GenBank: —MG696637 (18S rRNA gene).

Holotype: — China. Chongqing City: Simian Mountain , 28°36’32” N, 106°25’53” E, elevation 1150 m, on dead leaves of unidentified trees, 13 Jul 2016, collected by Shuanglin Chen (holotype, MCCNNU 3001!).

Etymology: —subochraceum refers to the deep chrome to mars yellow peridium.

Fruiting bodies in scattered groups, plasmodiocarpous or sporangiate, sessile, deep chrome to mars yellow; plasmodiocarps short, curved, slightly depressed, 0.6–3.0 mm long, 0.1–0.2 mm high, sporangia hemispherical to pulvinate, with a constricted base, 0.3–0.5 mm in diameter, 0.2–0.3 mm high; hypothallus inconspicuous, membraneous, hyaline; peridium a single layer compacted with lime granules, brittle, ornamented with minute holes on the outer surface; dehiscence mainly by longitudinal slit in plasmodiocarps or by stellate type in sporangia; columella absent; capillitium of profuse, rigid threads, attached to the base and peridium but easily break away from the base, gray under the dissecting microscope and hyaline by transmitted light, 1.4–2.3 μm in diameter, with branches and anastomoses, hardly expanded in the axils, usually beaded with rounded granules; spores dark brown in mass, pale brown by transmitted light, globose, (10.0)10.5–11.4(11.7) μm in diameter, warted, with clusters of large warts; plasmodium unknown.

Additional specimen examined: — China. Chongqing City: Simian Mountain, 28°36’32” N, 106°25’53” E, elevation 1150 m, on dead leaves of unidentified trees, 13 Jul 2016, collected by Shuanglin Chen (Paratype, MCCNNU 3002!).

Habitat: —on dead leaves of unidentified trees.

Distribution: —Currently known only from the type locality.

Remarks: —The genus Diderma Pers. is a large genus of the family Didymiaceae in the order Physarales ( Martin & Alexopoulos 1969) . It is characterized by double, sometimes single or triple layered peridium whose outer layer is calcareous or cartilaginous, by usually developed and calcareous columella and the limeless capillitium ( Martin & Alexopoulos 1969). Eighty species of the genus have been reported to date ( Lado 2005 –2018), and twenty-four of them are known in China ( Chen et al. 2013). The D. subochraceum is characterized by the single, deep chrome to mars yellow peridium with longitudinal or stellate dehiscence. The combination of these characters with undeveloped columella, profuse, rigid capillitium and spores ornamented with two types of warts is unknown in any other species in Diderma .

The new species seems to be mostly related to Diderma simplex (J. Schröt.) E. Sheld. Since both share the single peridium and absence of columella. However, the latter is characterized by crowded to heaped sporangia, membranous peridium, and sometimes well-developed hypothallus. The capillitium of D. simplex also shows expansions bearing lime-granules at the base which are absent in D. subochraceum . Furthermore, spores of D. simplex are violet, smaller (7–9 μm diam. according to Schoeter; 8–10 μm diam. according to Lister) and minutely warted ( Schoeter 1885, Lister 1925). Martin & Alexopoulos (1969) described D. simplex based on the collections from Silesia. Diderma subochraceum fits their description in certain respects, such as the absence of membranous peridium, and size and ornamentation of spores. But other characteristics obviously differ from D. subochraceum , including heaped sporangia, rare plasmodiocarps, brick-red peridium, tinted hypothallus and scanty capillitium.

Although double-layered peridium is common in species of Diderma , it does not mean that single peridium is unusual. At least eleven other species of Diderma are characterized by single peridium, and four of them have undeveloped columella, which are D. brunneobasale S.L. Stephenson & Nann. -Bremek., D. chondrioderma (de Bary & Rostaf.) Kuntze , D. evelinae (Meyl.) Kowalski and D. imperialis Emoto. However , it is easy to find at least one diagnostic feature when any two species are compared. Diderma brunneobasale can be distinguished from D. subochraceum by its depressed, white to brown sporangia, swelling capillitium and smaller spores (ca. 9 μm in diameter) (Stephenson & Nannengabremekamp 1990). Sporangia of D. chondrioderma and D. imperialis were usually stalked. Diderma chondrioderma also has large spores (10–15 μm in diameter) ( Martin & Alexopoulos 1969). The latter, in addition, has brown peridium and thickening part in capillitium ( Emoto 1929). Diderma evelinae is special in ovoid to sub-cylindrical sporangia, extensive hypothallus and dark, net-like capillitium ( Kowalski 1975).

Figures

FIGURE 2. Morphological characters of Diderma subochraceum. a A group of mature sporangia on dead leaves. b Opened sporangia and plasmodiocarps showing the absence of columella. c An opened sporangia showing the detachment between capillitium and the base (arrow). d The outer surface of peridium (SEM). e The inner surface of peridium (arrow, SEM). f Capillitium and spores (SEM). g Branches and anastomoses of capillitium (SEM). h Capillitial threads beaded with rounded granules (arrow, LM, DIC). i Spores. j A spore showing the small warts and cluster of prominent warts (SEM). Scale bars: a,b=1 mm; c=0.2 mm; d=20 μm; e=5 μm; f =30 μm; g=5 μm; h,i=10 μm; j=2 μm