Helicoon subglobosum Goh & C. H. Kuo 2018, sp. nov.
Creators: name: Goh, Teik-Khiang
name: Kuo, Chang-Hsin
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Fungi
Ascomycota
Dothideomycetes
Tubeufiales
Tubeufiaceae
Helicoon
Helicoon subglobosum

description: Helicoön subglobosum Goh & C.H. Kuo, sp. nov. FIGURE 1−4   
 MycoBank: MB 822429   
 Etymology: subglobosum, referring to the subglobose shape of the conidia.   
 Diagnosis: Differs from other Helicoön species in having large subglobose conidia which are borne singly on very short conidiophores.   
Colonies on natural substratum dark-brown, somewhat glistening, effuse. Mycelium partly immersed but mostly superficial, consisting of branched hyphae and short conidiophores bearing conidia; superficial hyphae ca 3.5−5.5 μm wide, pale yellowish-brown, smooth, branched, closely septate, slightly constricted at the septa which are 11.7−18 μm apart. Conidiophores macronematous, mononematous, cylindrical, erect, straight, arising as short branches more or less at right angles to the subtending hyphae, mid yellowish-brown or somewhat darker than the subtending hyphae, unbranched, non-septate, smooth, 11−19 μm long, (4.5−)5−6.5 μm wide. Conidiogenous cells monoblastic, integrated, terminal, determinate. Conidia solitary, dry, acrogenous, medium brown, helicoid, filament (6.5−)7.5−9.5 μm wide, smooth, distinct multiseptate, slightly constricted at the septa, tightly coiled (7−)8(−9) times in a clockwise direction to form a subglobose or broadly elliptical body, (57−)66−78(−87.5) μm long, (44−)58−72.5(−77) μm wide, with a length to width ration of (0.9−)1.1(−1.3), usually incorporated with mucilaginous substances such that no gaps are visible between adjacent coils, non-hygroscopic; conidial secession schizolytic at the deliminating septum of the conidiogenous cell, giving rise to a short pedicel of (7−)8−12.5 long and 5−6.5 μm wide at the base.  
 Material examined: ─ TAIWAN, Chiayi County, Juchi Township, on decaying wood submerged in a freshwater stream, 5 Feb 2017, Chang-Hsin Kuo, NCYU-K 3-2 (holotype: TNM F31003, deposited at National Museum of Natural Science, Taichung, Taiwan). Ex-type culture BCRC FU 30843, Bioresearch Collection and Research Centre (BCRC), Food Industry Research and Development Institute, Hsinchu, Taiwan. The rest of the single-spore isolates were kept at the Department of Plant Medicine, National Chiayi University (NCYU), Taiwan. GenBank accession numbers for rDNA derived from the type: LC316606 (ITS), LC316607 (ITS), LC316608 (ITS), LC316609 (ITS), LC316610 (LSU), LC316611 (LSU), LC316612 (LSU).   
 Cultural characteristics: ─ Conidia of H. subglobosum germinated in culture. Germination rate from single-spore isolation was 60%, but growth was extremely slow, with a growth rate of 0.2 mm per d. Colonies on PDA slants produced from single-spores reached 6 mm diam. in 5 wk at 20 °C. On PDA plates, colonies attained 1 cm diam. in 80 d at 20 °C. Mycelium from culture comprised ramifying hyphae which were hyaline to brown, septate, (2.6−)2.9(−3.2) μm wide. Chlamydospores were formed in culture, which were uscous, guttulate, globose, (7.1−)9.1(−10.7) diam. (FIG. 3).   
 Note: ─ Helicoön subglobosum is most similar to H. gigantisporum (Goh & Hyde 1996b) based on phylogenetic analysis (FIG. 5, 6) and morphological comparison. Both species have large fuscous conidia producing from short conidiophores which arise as lateral branches from repent hyphae. They both occur on submerged wood from freshwater environments. The conidial filaments in both species are of comparable width, and coiled in a clockwise direction (in the sense of Glen-Bott, 1955). However, they differ in several ways and are distinct species. The conidia in H. subglobosum are subglobose (i.e. having a mean length to width ratio 1.1), whereas in H. gigantisporum they are doliiform (i.e. having a mean length to width ratio 1.5). Conidia are much larger in H. gigantisporum (78−123 μm long and up to 100 μm wide), whereas conidia are 57−78 × 58−72.5 μm in H. subglobosum. The similarities and differences between these two species are summarised in Table 3.   
 H. subglobosum H. gigantisporum   
 Conidiophores   
Length 11−19 μm 6.5−14 μm  
Width (4.5−)5−6.5 μm 3−4.5 μm  
 Conidia   
Colour Medium brown Yellowish brown  
Shape of body Subglobose Broadly ellipsoidal  
Length of body (57−)66−78 μm 78−123 μm  
Width of body 58−72.5 μm (48−)56.7−90(−100) μm  
Length/width ratio (0.9−)1.1(−1.3) (1.4-)1.5(-1.7)  
Length of pedicel (7−)8−12.5 μm 4−9 μm  
Width of filament (6.5−)7.5−9.5 μm 6.5−10 μm  
Number of coils (7−)8(−9) (12−)13  
Direction of coiling Clockwise Clockwise  
Constriction at septa Slighted constricted Slighted constricted  
Wall texture Smooth Smooth  
 Habitat On wood submerged in freshwater On wood submerged in freshwater Known districbution Taiwan Australia, Thailand   
 Teleomorph Unknown Unknown   
 Phylogenetic placement Tubeufiaceae Tubeufiaceae   
 Including H. subglosum, there are now 18 species accepted in the genus Helicoön. A morphological comparison of these species was given in Table 4. A key to the genus is as follows.
description: Published as part of Goh, Teik-Khiang & Kuo, Chang-Hsin, 2018, A new species of Helicoön from Taiwan, pp. 141-156 in Phytotaxa 346 (2) on pages 145-148, DOI: 10.11646/phytotaxa.346.2.2, http://zenodo.org/record/13708256