species in the cosmopolitan genus hysterangium are characteristically hypogeous and range from 525 mm diam ( beaton et al . 1985 , castellano 1988 , castellano & beever 1994 , montecchi & sarasini 2000 ) . in recent years , we and our many collaborators have made more than 1  500 collections of hysterangium species in habitats from sea level to timberline and semiarid to wet tropics in all australian states and territories . we here describe a novel and relatively rare species with basidiomata to 55 mm broad , a giant in comparison to other species in the genus . to our knowledge once basidiomata were collected , we recorded fresh macroscopic characteristics , photographed representative specimens , and sliced and placed all collected specimens on the trays of a portable electrical circulating - air dehydrator set on low . in the laboratory , we prepared razor blade sections for microscope mounts in h2o , 5 % koh , cotton blue , and meltzer s reagent , respectively . microscopic measurements were taken in 5 % koh mounts after we determined that koh did not differ from fully hydrated h2o mounts . elliott & trappe , sp . nov . etymology : latin colossum ( colossal ) , in reference to its unusually large basidiomata ( to 55 mm broad ) compared to other species in the genus ( basidiomata typically < 25 mm broad ) . diagnosis : differs from all other known species of hysterangium by the exceptionally large size of the basidomata in combination with a tendency to occur in confluent clusters of 26 and the peridial invaginations into its gleba . type : australia : australian capital territory : gungahlin , yerrabi pond , near pond shore at end of james kirk st . 2010 , todd f. elliott , trappe 35048 ( canb  holotype ; bpi , bri , fh , k , mel , ny , osc 148802  isotypes ) . description : macrocharacters : basidiomata 1240  1455 mm , subglobose to turbinate or irregular and lobed , often confluent in clusters of 26 , hypogeous or sometimes emergent . peridium 0.351.5 mm thick , not readily separable from gleba , felty - glabrous , dirty white to pale brown , peridial surface of fresh specimens turns brown where bruised or exposed and reddens slightly in cross - section , larger specimens sometimes invaginated 210 mm into the gleba in a meandering pattern . gleba firm , slightly rubbery to cartilaginous , whitish translucent in youth , becoming green and finally dark olive by maturity , locules  0.5 mm broad , sterile base inconspicuous to prominent . columella obscure to well - developed , dendroid , greyish translucent , sometimes with reddish areas . basal attachment with clusters of white mycelia and fine rhizomorphs that mostly detach when specimens are separated from the soil . microcharacters : peridium thickness variable , typically 500600 m , consisting of a layered gradient of hyphae : pellis 180250 m thick , of loosely interwoven , thin - walled , light yellowish hyphae 212 m broad at the septa , most cells inflated to 415 m , with oxalate crystals adhered to surfaces of outer hyphae ; subpellis 240400 m thick , of interwoven , hyaline , thin - walled hyphae 220 m broad at the septa , most cells inflated to 520 m broad near the pellis but many sphaerocyst - like and inflated to 30 m broad , grading to 25 m broad and not inflated toward the gleba ; invaginated peridial veins lined with tissue similar to the peridial pellis but the channel filled with tangled hyphae with apical cells inflated to 40  35 m . glebal trama 100250 m thick , of hyaline , interwoven hyphae 25 m broad with gelatinized walls . spores 911  45 m , q = 2.4 , ellipsoid to subovoid with a slightly tapered truncate - cupped base no longer than 1 m , enclosed in a utricle , apex obtuse , wall surfaces under the utricle punctate roughened ; utricle irregularly inflated up to 2.5 m from the spore wall , not inflated in cotton blue mounts ; spores nonreactive in meltzer s reagent . basidia 3340  510 m , cylindric to clavate , 48-spored , sterigmata  1.5  1.5 m . distribution , habitat , habit , hosts , and season : australian capital territory and southeastern new south wales west of the great dividing range at 90 - 630 m altitude under various mixtures of eucalyptus albens , e. blakelyi , e. macrorhyncha , e. microcarpa , and e. sideroxylon , often with understory acacia deanei , a. doratoxylon , and a. paradoxa ; hypogeous or emergent in compacted soils ; june  august . additional material : 
 australia : australian capital territory : as per holotype , 8 aug . 2010 , todd f. elliott , trappe 34585 ( canb , osc 149381 , mel ) . new south wales : 10 km north of deniloquin on conargo road , wandook traveling stock route , 35 27 47 trappe 28671 ( canb , osc 148804 , mel , k , ny ) ; ibid . 2003 , trappe 28672 ( canb , osc 144805 , mel , k , ny ) 17 km west of finley , greens travelling stock route , 35 36 s , 154 24 4  e , elev . 2003 , trappe 28655 ( canb , mel , ny , osc 148803 ) ; goobang national park , currumbenya nature reserve , alongside wellington highway , amg 632830 e , 6352300 s , elev . the combination of the three macrocharacters noted in the diagnosis is unknown in other species of the genus . hysterangium inflatum sometimes produces compound basidiomata but never reaches the maximum size of h. colossum . it also lacks peridial invaginations , its peridium easily separates from the gleba , its spore surface is smooth , and its spore utricle tends to inflate evenly around its spores in contrast to the irregular inflation of h. colossum . we much appreciate the support of paul bartels , john casey , and mark brenner of warren wilson college , allein stanley of the schiele museum , and bob and babs strickland of walnut creek preserve . ecologist jacqui stol of csiro ecosystem sciences facilitated travel to several of the paratype sites . trappe s travel expenses were initially covered in part by the then csiro division of wildlife and ecology and later by the australian capital territory national parks . we thank the following collections for accessioning our material : bpi , bri , canb , fh , k , mel , ny , and osc .
hysterangium colossum sp . nov . , 
 with extraordinarily large basidiomata for the genus , is described from dry eucalyptus woodlands in the australian capital territory and southeastern new south wales . 
 it typically grows in confluent clusters and has a thick peridium often invaginated into the gleba .