Nigrosynnema C. F. Liao, K. D. Hyde & Doilom, 2025

Nigrosynnema C. F. Liao, K. D. Hyde & Doilom gen. nov.

Etymology.

The name refers to the characteristic black synnemata formed on natural substrate.

Description.

Saprobic on dead plant material. Sexual morph: undetermined. Asexual morph: Conidiomata synnematous or sporodochial. Synnemata unbranched, subcylindrical, globose to subglobose head, robust at base, olivaceous brown to black, straight or curved in the upper portion, consisting of bundles of parallelly arranged, tightly compacted conidiophores. Sporodochia stromatic, superficial, scattered or gregarious, irregular, pulvinate, with white mycelium surrounding an olivaceous green mass of conidia. Conidiophores arising from basal stroma, macronematous, mononematous, septate, unbranched or branched, straight or flexuous, thin-walled, subcylindrical, olivaceous brown, verrucose, consisting of a stipe and a penicillately branched conidiogenous apparatus consisting of a whorl of primary branches, each terminating in number of conidiogenous cells. Conidiogenous cells enteroblastic, monophialidic, integrated, terminal, clavate to subcylindrical, hyaline to pale olivaceous brown, smooth, often verruculose at base, with a conspicuous collarette. Conidia solitary, fusiform to ellipsoidal, aseptate, initially hyaline, becoming olivaceous brown to dark brown, longitudinally striated at surface, with a distinct dark basal hilum.

Type species.

Nigrosynnema guangdongense C. F. Liao, K. D. Hyde & Doilom

Notes.

Nigrosynnema resembles Striaticonidium in having fusiform to ellipsoidal conidia with longitudinal striations. However, it can be distinguished from Striaticonidium by having synnematous conidiomata, the absence of setae on the sporodochia, as well as support from molecular data. The synnematous conidiomata of Nigrosynnema are subcylindrical, flexuous, narrower towards the apex of the stipe, and robust at the base. The sporodochia are devoid of setae. However, in Striaticonidium , they are cylindrical to pyriform, broadened towards the apex, and have sporodochia covered by setae ( Lombard et al. 2016). The blastn search of NCBI GenBank revealed that two strains of Nigrosynnema, ZHKUCC 23-1014 and ZHKUCC 23-1015 , have sequence similarities of 98.37 %, 91.73 %, 89.70 %, 89.04 %, and 82.03 % to the type species of Striaticonidium ( Stri. cinctum CBS 932.69, ex-type) in LSU, ITS, tub 2, rpb 2, and cmdA sequence data, respectively. However, tef 1 - α sequence data of Stri. cinctum CBS 932.69 (ex-type) is unavailable in the NCBI database.

Nigrosynnema resembles Virgatospora described by Finley (1967) in having synnematous conidiomata, phialidic conidiogenous cells, and striated conidia. However, olivaceous brown to black synnemata in Nigrosynnema are subcylindrical, robust at the base, and narrower towards the apex of the stipe. The conidia in Nigrosynnema are aseptate, fusiform to ellipsoidal, and different from the septate, slightly curved conidia with a protuberant hilum of the type species of Virgatospora , V. echinofibrosa . Nigrosynnema can be distinguished from its closely related genera, as shown in Table 2 View Table 2 .

The phylogenetic analyses supported that our two strains ( ZHKUCC 23-1014 and ZHKUCC 23-1015 ) formed a distinct clade from other morphologically closely related taxa and constituted a well-supported clade related to Digitiseta with 94 % ML and 1.00 BYPP statistical support. The main distinguishing morphological characteristic between the two genera is the absence of hypha-like setoid structures in Nigrosynnema , whereas Digitiseta , introduced by Gordillo and Decock (2017), has short apical branches and digitated hypha-like setoids. Additionally, the conidial shape is fusiform to ellipsoidal in Nigrosynnema , while they are cylindrical in Digitiseta .

Based on morphological and molecular evidence, we introduce a novel asexual genus, Nigrosynnema , characterized by olivaceous to black synnematous or sporodochial conidiomata that produce phialidic, aseptate conidia in black, slimy, glistening masses or heads. The conidia are fusiform to ellipsoidal, aseptate, longitudinally striated, and olivaceous brown to dark brown.