Digitodesmium recurvum sp. nov., recorded from freshwater habitats in Hong Kong, is described and illustrated. Diptodesmium recuruum is characterized by chiroid, olivaceous brown, euseptate conidia composed of 4-6 apically recurved arms. Characteristics of the conidia of the two known species of Digitodesmium are summarized, and a comparison with
other similar species is also provided.published_or_final_versio

Ho, WH

Hodgkiss, IJ

Hyde, KD

Mycologia

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Title Digitodesmium recurvum, a new species of chirosporoushyphomycete from Hong KongAuthor(s) Ho, WH; Hyde, KD; Hodgkiss, IJCitation Mycologia, 1999, v. 91 n. 5, p. 900-904Issued Date 1999URL http://hdl.handle.net/10722/53361Rights Creative Commons: Attribution 3.0 Hong Kong License.\.~colo,qn, $11(5 ) ,  11109, pp. 000-904. 'C 1990 b y  The Rl!cological Societ\ of .k~ierica,Lawrence, IiS 66041-8897 Digitodesmium recurvum, a new species of chirosporous hyphomycete from Hong Kong Wai-Hong Ho' Kevin D. Hyde I. John Hodgkiss Centre for Research zn Fungal Dzversztj, Department of Ecology and Bzodzversztj, Thr L~nzvers~tj of Hong Kong, Pokfulam Road, Hong Kong Abstract: Digitodesmium recurvum sp. nov., recorded from freshwater habitats in Hong Kong, is described and illustrated. Diptodesmium recuruum is character- ized by chiroid, olivaceous brown, euseptate conidia composed of 4-6 apically recurved arms. Character- istics of the conidia of the two known species of Dig-itodesmium are summarized, and a comparison with other similar species is also provided. Key Words: aquatic fungi, lignicolous fungi, sys- tematics, taxonomy In a continuing study of freshwater mycota in the tropics (Ho et a1 1997, 199910, c, Goh et a1 1998b, Hyde et a1 1998), an undescribed dematiaceous hy- phomycete was found on wood baits of Machilus ue- lut ina and on other naturally occurring wood sub- merged in a small stream in Hong Kong. This fungus produces chiroid conidia in sporodochia. Critical ex- amination of the morphological characters suggested placement in the genus Digitodes~miumP. M. Kirk. The genus Digitodesmium was erected by Kirk (1981) to accommodate a single species, Dig. elegans P. M .  Kirk, found on rotten wood of Fagus s~luatica,  Quercus robom's and Taxus baccata(?) from Surrey, England. Digitodesmium elegans is characterized by the presence of punctiform, sporodochial conidiom- ata and semi-macronernatous, mononematous conid- iophores. The conidiogenous cells are discrete, mon- oblastic, and do  not proliferate; the conidia are ho- loblastic, composed of a truncate basal cell on which (2-)3-4(-6) arms are formed in different planes. The arms are straight, cylindrical, vertical, appressed to each other or slightly divergent and euseptate, and the conidia secede schizolytically (Kirk 1981). D i p -todesmium remains monotypic and its teleomorph is presently unknown. The species of Digitodesmium col-.Accepted f v t - publication XIa\ 10, 1099 Email: 11hho~g1-adrlate~I1k~1.11k lected in Hong Kong is significantly different from the type species and is therefore described as new. Digitodesmium recurvum W. H. Ho, K. D. Hyde et I. J. Hodgkiss, sp. nov. FIGS. 1-9 Conidion~atasporodochia, sparsa, punctiformia, pulvina- ta, atrobrunnea vel atra, 100-300 pm diameter. Mycelium in substrato plerumque immersum, ex hyphis brunneis, lae- ~ l b u s ,  tenuitunicatis, septatis, ramosis compositum. Conidi-ophoru semi-macronematosa, mononematosa, pallide brun- nea, laevia, tenuitunicata, non-ramosa, cylindrica. flexuosa, 6-14 X 3-5 pm. Cellular conidiogenr monoblasticae, in con- idiophoris incorporatae, terminales, determinatae, pallide brunneae, laeves, tenuitunicatae. Conidin acrogena, holo- blastica, solitaria, pallide brunnea, cheiroidea, 30-45 X 12-21 pm, euseptata, cum 47(-8)  rami praedita, verticalia; crl-lula basilan's 3.5-6 X 3.5-5 pm, pallide brunnea. truncata, lae~ia,  tenuitunicata; rami discreti, non-ramosi, dense ap- pressi vel divergenti, cylindrici, 25-41 X 5-7 pm, 5-10-eu- septati, ad septa modice constricti, pori septarum praediti. ad apicum recurvati. Conidiorz~rn .srcrs.tio schizolytica. Conidiomata sporodochial, scattered, punctiform, pulvinate, dark brown to black, 100-300 ym diame- ter. (FIG. 1) .  1~yceliunzmostly immersed in the sub- stratum, composed of b r o ~ m ,  smooth, thin-walled, septate, branched hyphae. Conidiophores semi-macro-nematous, mononematous, pale brown, smooth, thin-walled, unbranched, cylindrical, flexuous, 6-14 X 3-5 pm (FIGS. 3, 4). Conidiogenous cells monoblas-tic, integrated, terminal, determinate, pale broivn, smooth, thin-walled, non-proliferating (FI~; .  4),  giv-ing rise to a single crop of conidia that mature syn- chronously. Conidia acrogenous, holoblastic, solitary, pale brown, chiroid, 30-45 X 12-21 pm (x = 39 X 16 ym, n = 30), euseptate, with 4-7(-8) arms verti- cally inserted on basal cells in different planes (FI(,s. 2, 5-9); basal cells 3.5-6 X 3.5-5 ym, pale brown, truncate, smooth, thin-walled (FIc:~. 8, 9) ;  arms dis-crete, unbranched, closely appressed to each other or divergent at maturity, cylindrical, 25-41 X .3-7 ym, 5-10-euseptate, slightly constricted at the septa, with conspicuous septa1 pores surrounded by marked pigmented rings 1-1.5 ym wide, appearing as doli- pores in side view, mostly with a narrowed, recurved apical cell (FIGS. 5-9). Conidial secession schizolytic (Frcs. 6, 9).  ~tlatm'al examined. HONG KONG. Tai Po Kau Forest Stream, on submerged wood, 27 Jun 1996, K. D. Hydr M'H I FIGS. 1-9. Dig. recuruum (from HOLOTYPE). 1. Colonies on woody substratum. 2. A sporodochium with conidial mass attached to conidiophores. 3. Conidiophores viewed from above, illustrating their circular lumina. 4. Mass of conidiophores. Note that the arrowed conidiophore is in side view. 5. Conidia with parallel euseptate arms vertically inserted on basal cells in different planes. Note that the arms of the conidium are closely appressed, while another is slightly divergent. 6. Conidia with divergent arms. Note that the arms are recurved at the apex. 7. Closer view of the lower portion of a conidium. Note the conspicuous conidial septa1 pores surrounded by marked pigmented rings (R). The rings appear as dolipores (D) in side view. 8. Conidium at the basal portion illustrating the pigmented rings (R) at the conidial septum. 9. Basal portion of a conidium, illustrating the pigmented ring of conidium delimiting septum. The ring appears as dolipore-like (D) in side view. Bars: 1 = 500 pm; 2 = 20 pm; 3-6 = 10 pm; 7-9 = 15 pm. I.T,%BLL Comparison of conidial morphology in species of Digztodesmium <:onidia Basal cell5 Conidial arms Dig. recz~ruztm Dig. elvfiuns (This paper) (Kirk 1981) Color Pale brown -Diameter 30-45 pm long, 12-21 pm wide 45-60 pm long Wall Smooth Smooth Septa1 pores (:onspicuous in all conidial de- Inconspicuous limiting and conidial septa, surrounded by a marked ring of pigmentation, visible in lat-era1 view as a dark brown disc 1-15 pm wide (;olor Pale brown -Diameter 3.5-6 pnl high, 3.5-5 p n ~  wide 2.5-5 pm wide Truncate Yes Yes Number of arms (2-14-6(-7) ( 2 - )3-4~-6) Diameter 25-41 pm long 5-7 pm wide 3-6 pm diarn Apical cells hfostlb narrow and I ecurved Occasionally with a hvaline gelat- Constriction at the septa Slight11 Branching-No  Number of 5epta 6-10 " Data not available 300 H 98 [HOLOTYPE: HKL'(M) 4.5521. 27 Ilec 1997. M! H Ho H 638 [HKU(M) 87391, zbzd. on submerged ,Mach-zlzir uelutznrc wood ba~t. 29 Mar 1997, 11.' H Ho H 383 [HKU(M)60431 Etymology. In reference to the recurved conidial arms. kizown distribution. Hong Kong. Inbitat .  Saprobic on decaving wood in streams. Teleornorph. Unknown. Commentarj. Our initial placement of Dig. wcur-z~urnwas in the genus Dictyospo~.i.um,based on the similarity between our species and Dic. giganticunz Goh & K.  D. Hyde, Djc. heptasporum (Garov.) Damon and Die. subrarnanianii B. Sutton. These species have chiroid euseptate conidia with arms inserted in the basal cells in different planes, with most arms being terminated with a recurved hook (Goh and Hyde 1999). The conidial arms of Dig. recurvurn become divergent at maturity, but those of the latter three species of Dictyospo7-ium remain closel~~appressed (Goh and Hyde 1999). The corlidial arms of Die. hep- tasporum may become separate only under pressure (Goh and Hvde 1999). Dictyosponum cocopf-lilum Bat. and Die. mirrorze.~icunz Matsush. also produce eusep- tate chiroid conidia with arms inserted in the basal cells in different planes, but the tips of the arms are straight and do  not become divergent at maturity (Coh and Hyde 1999). We also considered placing this species in genera such as Cheirornoniliophora S. S. Tzean & J. L. Chen (1990), C~f~~i?-om~c~lLaHiih11 (Sutton 1985), Dirrani-inous cap No  No 9-1 2 diorz Harkn. (Peek and Solheinl 1958), Pseztdodictjos-poriurn hlatsush. (1971) and Rarniconidiifo-a B. Sut-ton, <.:arrnaran X. A. I. Ronlero (1996) since all pro- duce chiroid, euseptate conidia. The conidial arms in Ch~ironzonil ophora and Pseuclodict?ospollum, how-ever, do not become divergent, while the conidiogen- ous cells of Cheirornjcella, Dicrarlidior~ and Ramico~zi-N'izfera are able to proliferate. Our species agrees with the generic delilleation of Dzgztodesmzunz (Kirk 198 1 )  and thus it is assigned to this genus. Digitodesrn,iurn rec.urvu'm differs from the type spe- cies, Dig. eLega?zs, in having shorter conidia with arms which are recurved at the apex. In Dig. el~gan,s,the conidial arms are straight and each arm possesses a hyaline gelatinous cap at the tip (Kirk 198 1) . Conid-ial morphology of the hvo species of Digitocl~smiurnis conlpared in Ti\~r.l-I. In Dig. reczlrvum, a central pore surrounded by a markcd ring of pigmentation are present in all co- nidial deliniiting septa as well as in the conidial septa. The septal pores ksith rings of pigmentation appear as dolipores in lateral view. In the ascomycetes and their anamorphs, the septa are perforated by central, simple pores which can be resolved using transmis- sion electron microscopy (Markham 1994). This cen- tral septal pore is more prominent in sonle thick- walled spores (e.g., Goos 1971, Ho et a1 1999a) or cells of'ascorna wall, such as the &funk pores (Jensen 1985) and the peridial pores (Cannon 1995) and can be resolved at light microscope level. --- Septa1 pores are not visible, and the pigmented rings are absent in the conidia of Dig. elegans (Kirk 1981). Pigmented rings surrounding the septal pores have been recorded in euseptate conidia [as in Can-alisporium pallidum Goh, W. H. Ho & K. D. Hyde (Goh et a1 1998a)], distoseptate conidia [as in @ri-cularia peruamazonica Matsush. (Matsushima 1993) 1 or conidia with distosepta and eusepta [as in Janetia curuiapicis Goh & K. D. Hyde (Goh and Hyde 1996)l. This pigmented ring can be a generic feature (e.g., all species of Canalisporium possess this structure; Goh et a1 1998a), or a specific feature (e.g., only some species of Bactrodesmium possess this structure; Ellis 1971). Diptodesmium is characterized by chiroid, eusep- tate conidia produced on sporodochia (Kirk 1981). Morphologically, this genus is similar to Cheiromyces Berk. & Curtis, except that the latter produce disto- septate conidia (Sutton 1985). Sutton (1985) ob- served that cells in the conidia of Diptodesmium have two features characteristic of distosepta, i.e., (i) the lumina are reduced, and (ii) the septal walls do not fully abut onto the periclinal walls. Based on this type of septation, Sutton (1985) commented that Dipto-desmium should possibly be synonymised with Chei-romyces, which produces chiroid distoseptate conidia, but he hesitated to do so. In Dig. recurvum, the conidial cells also have re- duced lumina due to the thickening of the cell walls. Although reduced lumina or thickened cell walls are commonly found in distoseptate conidia, these char- acteristics are not restricted to distoseptate conidia. The conidia of Acrodictys M. B. Ellis (1971), Bactro-desmium Cooke (Ellis 1959), Canalisporium Nawawi et Kuthub. (Goh et a1 1998a) and Cancellidium Tu-baki (1975) have reduced cell lumina, but they are considered euseptate. Furthermore, the septal walls of mature thick-walled conidia, such as those of Ac-rodictys, Bactrodesmium and Canalisporium, also ap- pear to be discontinuous with the periclinal wall when observed at X 1000 magnification using immer- sion oil (Ho pers obs). These septal walls and peri- clinal walls are clearly continuous in the immature, thin-walled conidia of these species. The apparent discontinuity in the walls of mature conidia is due to the artifacts brought about by light refracting through the thickened wall. Possibly, Sutton's (1985) observation on the discontinuity of the septal walls and periclinal walls may also have been the result of artifacts. His observation on the reduced conidial cell lumina do not warrant consideration of such conidia to be distoseptate. For these reasons, we retain the genus Digitodesmiurn. We thank Dr. T. K. Goh of The University of Hong Kong for his valuable comments on the manuscript. The staff in the Photographic Unit of the Faculty of Science, The Uni- versity of Hong Kong are thanked for photographic assis- tance. Thanks are extended to Ms. Helen Y M. Leung for technical assistance. W. H. Ho thanks The University of Hong Kong for the award of a postgraduate studentship. LITER4TURE CITED Cannon PF. 1995. Studies on fungi with isthmoid asco-spores: the genus Vialaea, with the description of the new family Vialaeaceae. Mycol Res 99:367-373. Ellis MB. 1959. Clasterosporium and some allied Demati- aceae-Phragmosporae. I. Mycol Paper 72:l-89. , ed. 1971. Dematiaceous hyphomycetes. Kew, Eng- land: Commonwealth Mycological Institute. 608 p. Goh TK, Ho WH, Hyde KD, Whitton SR, Umali TE. 1998a. New records and species of Canalisporium (Hyphomy-cetes). with a reklsion of the genus. Can J Bot 76:142- 152. , Hyde KD. 1996.Janetia curviapicis, a new species, and an emended description of the genus. Mycologia 88:1014-1021. --. 1999.A rellsion of the genus Dictyosporium, with descriptions of three new species. Fung Divers 2: 65-100. - , Ho MW. 199813.Aquaphila albicans gen. et sp. nov. (Hyphomycetes) from submerged wood in the tropics. Mycol Res 102:587-592. Goos RD. 1971. Listeromycetes insignis refound. Mycologia 63:213-218. Ho M'H, Goh TK, Hyde KD, Hodgkiss, IJ. 1999a. Studies of conidial anatomy and conidiogenesis in Sporoschisma nigroseptatum using light and electron microscopy. Can J Bot 76:1614-1623. , Hyde KD, Hodgkiss, IJ. 1997. Xscomycetes from tropical freshwater habitats: the genus Savoryella, with two new species. Mycol Res 101:803-809. . 1999b. Ascal ultrastructural study in Annulatascus hongkongensis, a freshwater ascomy- cete. Mycologia 91 :885-892. ---. 1999c. Ultrastructure of Annula-tascus aquaticus sp. nov., a freshwater ascomycetes on submerged wood from Hong Kong. Fung Divers 2119- 128. Hyde KD, Ho WH, Tsui KM. 1998. The genera Aniptodera, Halosarphka, Nais and Phaeonectri~llafrom freshwater. Mycoscience (In press). Jensen JD. 1985. Peridial anatomy and Py~enomycete tax- onomy. Mycologia 77:688-701. Kirk PM. 1981. New or interesting microfungi. Trans Br My- col Soc 77:279-297. Markham P. 1994. Occlusions of septal pores in filamentous fungi. Mycol Res 98:1089-1106. Matsushima T. 1971. Microfungi of the Solomon Islands and Papua-New Guinea. Kobe, Japan: Pub1 by author. 78 p 169 pl. . 1993. Matsushima mycological memoirs. No. 7. Kobe, Japan: Publ by author. 75 p. Peek GI,Solheim WG. 1958. The hyphomycetous genera of H. W. Harkness and the ascomycetous genus Ckis-tosoma Harkn. Mycologia 50:844861. Sutton BC. 1985. Notes on some deuterornycete generawith cheiroid or digitate brown conidia. Proc Indian Xcad Sci (PI Sci) 94:229-244. , Carmaran CC, Romero A.1996. Ramiconidiqera,a new genus of hyphomycetes with cheiroid conidia from Argentina. Mycol Res 100:1337-1340. Tubaki I(. 1975. Notes on the Japanese hyphomycetes. 171. Cancellidium,a new hyphomycetes genus. Trans Mycol Soc Japan 16:357-360. Tzean SS, Chen JL. 1990. Cheiromoniliophora pkgans gen. et sp. noe (Hyphornycetes), Mycol Res 94:424-427. 

Digitodesmium recurvum, a new species of chirosporous hyphomycete from Hong Kong

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Digitodesmium recurvum, a new species of chirosporous hyphomycete from Hong Kong

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