Most peatswamp forests can be found in tropical rainforests where peat is submerged for most of the year and characterised by low nutrient contents and high acidity due to lack of fully decomposed plant materials (Page et al. 1999, 2011; Jackson et al. 2009; Lampela et al. 2016; Ratnayake 2020). Peatswamp forests are unique ecosystems due to their high species diversity and significant role in maintaining a stable global climate. They function as carbon sinks, storing twice as much carbon as all global forest biomass (Hakim et al. 2017; Fujimoto et al. 2019; Shuhada et al. 2020). Beyond carbon storage, peatlands offer valuable benefits. They play vital roles in the water cycle, storing and filtering water and mitigating floods by slowing peak flows. Home to diverse plants and animals, these wetlands support millions of people. Additionally, they hold archaeological relics and provide insights into past environmental conditions through their peat layers, aiding predictions about the future climate (Parish et al. 2008; Posa et al. 2011; Minayeva and Sirin 2012; UNEP 2022). Asian peatlands are amongst the most diverse and geographically extensive in the world, with over 160 million hectares and the majority of tropical peatlands are found in Southeast Asia (e.g. Brunei, Indonesia, Malaysia, Papua New Guinea and Thailand) (UNEP 2022).

These habitats support many flora, including an extensive number of bryophytes, ferns and palms (Arecaceae) (Prentice 2011; Rieley 2016). Arecaceae comprises iconic monocotyledonous flowering plants belonging to 188 genera and 2,585 species that are distributed throughout tropical and subtropical areas of the world. However, they are most diverse in highly threatened moist tropical forest habitats (Dransfield et al. 2008; Palmweb 2023; POWO 2023). In peatswamp forests, many palm species, such as Areca macrocalyx Zipp. ex Blume, Calamus concinnus Mart, Cyrtostachys renda Blume, Eugeissona tristis Griff, Eleiodoxa conferta (Griff.) Burret, Licuala longicalycata Furtado, L. paludosa Griff, Metroxylon sagu Rottb and Nenga pumila (Blume) H.Wendl. ex Schaedtler can be found (Calabon et al. 2022), exerting different biological functions.

Several studies on palm fungi have focused on saprobic, endophytic and plant pathogenic life modes from different habitats worldwide (Hyde 1988; Taylor et al. 1999; Fröhlich and Hyde 2000; Fröhlich et al. 2000; Hyde et al. 2000; Taylor and Hyde 2003; Pilantanapak et al. 2005; Lumyong et al. 2009; Liu et al. 2010; Wikee et al. 2013; Konta et al. 2016a, 2016b, 2016c, 2017, 2020a, 2020b, 2020c, 2021a, 2021b, 2023; Chou et al. 2019; El Meleigi et al. 2019; Kinge et al. 2019; Marin-Felix et al. 2019; Chen et al. 2020; Mapook et al. 2020; Zhang et al. 2020; Tian et al. 2022). Even though many palm trees grow in peatswamp forests, there are few records of fungal studies in these environments, mostly reported from Thailand (Pinruan et al. 2002, 2004a, 2004b, 2004c, 2004d, 2007, 2008, 2010a, 2010b, 2014; Pinnoi et al. 2003a, 2003b, 2004, 2006, 2009, 2010; Voglmayr and Yule 2006; Sivichai and Boonyuen 2010; Boonyuen et al. 2012), of which many lack molecular data. Pinnoi et al. (2006) studied saprobic fungi on dead palm material in the Sirindhorn peatswamp forest, Narathiwat Province, Thailand and listed 462 ascomycetous and basidiomycetous taxa from various parts of palm materials (such as dry, damp and submerged palm materials), based on morphological identification and also recorded five sporidesmium-like taxa. Pinnoi et al. (2009) identified 88 fungal species from 212 collections of Calamus sp. in Thailand, with six records resembling sporidesmium-like taxa.

Distoseptispora K.D. Hyde, McKenzie & Maharachch belongs to Distoseptisporaceae, Distoseptisporales, Sordariomycetes, Ascomycota and comprises sporidesmium-like taxa (Wijayawardene et al. 2022). Su et al. (2016) proposed Distoseptisporaceae to accommodate sporidesmium-like taxa with Distoseptispora as the type genus and D. fluminicola McKenzie, Hong Y. Su, Z.L. Luo & K.D. Hyde as the type species. Subsequently, Luo et al. (2019) introduced Distoseptisporales to accommodate Distoseptisporaceae, based on multigene phylogenetic analyses of LSU, SSU, rpb2 and tef1-α sequence data. Distoseptispora is characterised by short, septate, olivaceous to brown conidiophores. The conidiogenous cells are monoblastic and determinate, bearing acrogenous conidia that are brown, euseptate, distoseptate or muriform and cut off by cross walls at the basal cell with a basal scar (Yang et al. 2018). The genus exhibits morphology similar to Sporidesmium, but can be distinguished by having shorter conidiophores and darker conidia with pale round apexes (Su et al. 2016). To date, Distoseptispora comprises 65 species listed in the MycoBank database (https://www.mycobank.org/; Accessed in August 2023), with molecular data available for all reported species in the GenBank. The estimated divergence time for Distoseptisporaceae is approximately 44.21 million years ago (MYA), after the Tertiary–Cretaceous extinction event (Hyde et al. 2020), which could have created conducive conditions for Distoseptispora to thrive as a saprobe on various hosts (Phukhamsakda et al. 2022).

Peatswamp forests are unique, endangered ecosystems and their fungal biodiversity is little known. Therefore, in the current study, we aimed to study fungal species on different palm materials from peatswamp forests in Thailand, based on morphology and phylogeny. This study introduces three new species, Distoseptispora arecacearum, D. eleiodoxae and D. narathiwatensis, associated with Eleiodoxa conferta, Eugeissona tristis and Licuala paludosa from a peatswamp forest in Narathiwat Province, Thailand, based on morphological characteristics coupled with multigene phylogenetic analyses (ITS, LSU, rpb2 and tef1-α).

Peatswamp forests are unique habitats found in only a few regions worldwide (Jackson et al. 2009). The destruction caused by humans threatens them; hence more extensive studies on fungal identification are needed before the extinction of fungal species. Pinnoi et al. (2006, 2009) recorded sporidesmium-like taxa on the palm species Eleiodoxa conferta and Calamus sp. in Sirindhorn peatswamp forest, Narathiwat, Thailand, based on morphological data. In this study, three new Distoseptispora species (D. arecacearum, D. eleiodoxae and D. narathiwatensis) from peatswamp forest in Thailand are introduced, based on multilocus phylogenetic analysis (ITS, LSU, rpb2 and, tef1-α) (Fig. 1) and morphology (Figs 2–4).

The fungal diversity in peatswamp forest has not been well studied and a few previously studies (Pinruan et al. 2002, 2004a, 2004b, 2007, 2008, 2010a, 2010b, 2014; Pinnoi et al. 2003a, 2003b, 2004, 2006, 2009, 2010; Voglmayr and Yule 2006; Sivichai and Boonyuen 2010; Boonyuen et al. 2012) show a high fungal diversity in this habitat, especially in Thailand, but some of the previous studies (Pinruan et al. 2002, 2007, 2014; Pinnoi et al. 2003a, 2003b, 2004, 2006, 2009; Sivichai and Boonyuen 2010) lack molecular data. As only morphological data are insufficient to identify a fungal species (Chethana et al. 2021; Maharachchikumbura et al. 2021), studying the fungal diversity by combining morphological and molecular data are required and this has been followed in this study.

Except for Distoseptispora hyalina J. Yang & K.D. Hyde and D. licualae Konta & K.D. Hyde, most Distoseptispora species have been recorded as having an asexual morph and their characters, such as size, shape, colour and the number of septa in conidiophores and conidia, are crucial for distinguishing species. Morphologically, Distoseptispora is similar to Ellisembia Subram and Sporidesmium Link; therefore, it is problematic to recognise Distoseptispora species by only morphological signatures (Su et al. 2016; Hyde et al. 2019; Luo et al. 2019; Yang et al. 2021). Different studies have explored the taxonomy of Distoseptispora using various combinations of gene regions, such as combined ITS, LSU (Tibpromma et al. 2018), combined LSU, ITS, rpb2 (Monkai et al. 2020) or combined LSU, ITS, tef1-α and rpb2 (Zhang et al. 2022). In our study, we constructed the phylogenetic tree using concatenated ITS, LSU, rpb2 and tef1-α. In this study, Distoseptispora clematidis (MFLUCC 17-2145) and D. nabanheensis Jing W. Liu, X.G. Zhang & Jian Ma (HJAUP C2003) formed a sister clade, consistent with previous research (Liu et al. 2023). However, D. clematidis (KUN-HKAS:112708) appeared separated from these two taxa, presenting an unresolved relationship. The phylogenetic relationship amongst these three taxa is not comparable with the previous studies due to the lack of all these taxa together in their phylogenetic trees (Afshari et al. 2023; Liu et al. 2023). The unresolved clade’s origin may stem from the lack of rpb2 sequence data for D. clematidis (KUN HKAS:112708) in contrast to the other two taxa where this gene region is available. This suggests that different taxon sampling and protein-coding sequences can influence the topology of the tree. However, further studies are essential to validate this hypothesis.

Morphologically, some taxa that share similarities exhibit distinct phylogenies. For instance, D. arecacearum shares a morphological resemblance with D. dehongensis, although they are phylogenetically distinct. Similarly, D. eleiodoxae shows morphological similarities to D. tropica, but resides in a separate clade in the phylogenetic tree. Distoseptispora narathiwatensis forms a sister clade with D. saprophytica despite the differences highlighted by the pairwise comparison of ITS, LSU and other genetic markers. These encompass 22/580 bp (3.8%) and 16/870 bp (1.8%) differences for ITS and LSU, respectively, excluding gaps. Moreover, distinctions in the morphology of conidiophores and the absence of acrogenous conidia further contribute to the differentiation between D. narathiwatensis and D. saprophytica. Our study confirmed the necessity of associating molecular data with morphological characters to distinguish them, as previously demonstrated in other studies (Su et al. 2016; Hyde et al. 2019; Luo et al. 2019; Yang et al. 2021; Ma et al. 2022).

To date, the majority of Distoseptispora species have been reported from China (42 species) and Thailand (23 species), primarily on dead plant materials in freshwater (44 species) and terrestrial (21 species) habitats. In most cases, the hosts are unknown. Although in 19 cases, their hosts have been identified, two of which have been reported from palm, including D. palmarum from Cocos nucifera and D. licualae from dead leaves of Licuala glabra in terrestrial habitats (Hyde et al. 2016, 2021; Su et al. 2016; Xia et al. 2017; Tibpromma et al. 2018; Yang et al. 2018; Luo et al. 2019; Phookamsak et al. 2019; Monkai et al. 2020; Phukhamsakda et al. 2020, 2022; Song et al. 2020; Sun et al. 2020; Dong et al. 2021; Li et al. 2021; Shen et al. 2021; Jayawardena et al. 2022; Ma et al. 2022; Zhai et al. 2022; Zhang et al. 2022; Konta et al. 2023; Liu et al. 2023). Distoseptispora species have been recorded as saprophytes and their reported limited geographic distribution (China and Thailand) is most likely due to increased attention by mycologists in these areas on saprophytic fungi in aquatic and terrestrial habitats. This study shows that there is much to be done in this regard. Ongoing and future investigations will reveal the diversity and functions of these microorganisms in this ecosystem.