Clavulina sprucei (Berk.) Corner, Monograph of Clavaria and allied Genera, Annals of Botany Memoirs 1: 341 (1950)
≡ Clavaria sprucei Berk., Hook. Journal of Botany and Kew Garden Miscellany 8:276. (1856), nom. nov.
Clavulina sprucei was collected by Richard Spruce in 1853 in Brazilian territory, and in 1856, it was officially published by Berk under the name Clavaria sprucei. However, in 1950, it was synonymized to Clavulina sprucei, remaining as the current name. The species features a coralloid basidiome with dichotomous branching. The branches are whitish to pale creamy white throughout the extension; the hymenium is not well defined, amphigenous on central branches and possibly portions of the stipe, concolor.
The species Clavulina sprucei deserves to be considered for inclusion on the IUCN Red List due to its geographically limited distribution to three countries in South America, with few occurrences recorded over 167 years since its description. Additionally, the loss of its habitat makes the species threatened.
The Amazonian-origin species is documented in three localities. In the Western Amazon, it is known from the type locality in the Vaupés basin in northern Brazil, in white sand forests dominated by Dicymbe uaiparuensis and Aldina sp. in the southern part of Colombia (Vasco-Palacios, 2018), and in Guyana. In this same country, over 1,500 km from the type locality, it was identified by Henkel et al. (2011) in areas of predominantly monodominant forests, mainly consisting of Dicymbe corymbosa and occasionally with D. altsonii. Additionally, the species is expected to occur in white sand forests in Peru.
For the quantitative assessment of the taxon, a survey of the distribution proportion of its hosts resulted in a restricted occurrence to South America. It is expected that the fungus follows the distribution of plants in the Amazon biome. As the species is confined to these specific and limited habitats, the total number of locations where it can occur is estimated to be approximately 55 forests primarily dominated by Dicymbe corymbosa, corresponding to a 40 km territorial expanse in Guyana (Degagne et al. 2009), and forest fragments with a higher occurrence of Aldina insignis and D. uaiparuensis (without quantitative data described in the literature for these species). For D. corymbosa, a total of 62-63 mature individuals per locality can be inferred associated with the plant species. Furthermore, the population of C. sprucei is estimated to be over 3527 mature individuals (Henkel et al. 2012).
Studies by Henkel et al. (2011), (2012), mark the first reports of the species since 1853-1856, as well as a range extension of almost 1,500 km, however, the number of collections over time has been recording between 2-3 specimens of C. sprucei, in studies whose theme evaluated the mycorrhizal potential of the genus Dicymbe. However, Delevich et al. (2021) studied the panorama of the ectomycorrhizal relationship in seedlings of a monodominant neotropical Dicymbe tree during one year in Guyana. In this study, there was an increase in the number of records of C. sprucei (8-9 individuals) in contrast to other previous studies that had only recorded between 2-3 individuals. From this, for population trend analysis, the following data set was used: Number of known sites (55) + Number of unknown sites (70)*Number of specimens (~3)/Sites (1)* Ramets ( 3) + Application of Percentage = resulting in 68.5%. Thus, a population increase of C. sprucei was inferred in relation to collections prior to the work by Delevich et al. (2021).
Population Trend: Improving
Clavulina sprucei is an ectomycorrhizal species found in forests dominated by Dicymbe corymbosa in Guyana and in white sand forests dominated by D. uaiparuensis and Aldina sp. in Colombia (Henkel et al. 2011; Vasco-Palacios et al. 2018). This fungal species can be found growing dispersed, gregariously in groups on partially decomposed leaves, on small woody substrates in the forest, or even on mounds of roots and pseudo stems of D. corymbosa (Henkel et al. 2011). It is usually frequent during May to July in the rainy season and also from December to January (Henkel et al. 2011). Furthermore, the species is recognized in the field for its small, whitish to cream basidiomes (Henkel et al. 2011).
The basidiomes are generally superficially invaded by an as-yet-unidentified sordarial parasite that forms small black spots (Henkel et al. 2011).
Clavulina sprucei faces the threat of the accelerated process of anthropization in the South American biomes, such as increasing rates of loss of tropical forest cover due to changes in land use, selective logging, and the risk of fire in previously intact forests. The percentage loss is largely caused by cyclic silviculture and changes in agricultural practices. Climate change also poses a threat to C. sprucei. For instance, the 2015-2016 El Niño revealed a widely indiscriminate increase in forest loss in 2016 in most forest fragments, both within and outside protected areas (Hansen et al. 2020). Fires are more prevalent in El Niño years due to drought, compromising the life forms that inhabit the region, including the plant species D. corymbosa, D. altsonii, D. uaiparuensis, and A. insignis, which are identified as hosts for mycorrhizal association with C. sprucei.
No conservation action is currently in place for this species. Thus, the protection of the habitat and the plant host in which the species is found is necessary. Efforts to increase protected areas in forests primarily dominated by D. corymbosa, D. altsonii, D. uaiparuensis, and A. insignis, and/or adjacent areas, would be important to reduce land use, as well as the restoration of natural forest cover in degraded areas. New field expeditions are also needed to search for new occurrences to document the distribution, abundance, and ecology of the species. Additionally, social actions aimed at protecting the environment and educating society about fungi through their environmental importance and applications in the food and medical industries would also contribute to including C. sprucei and fungi in general in conservation policies.
The available information on C. sprucei reveals that the species exhibits a discontinuous distribution and distinct trends. In the central and western regions of the Amazon, this species is rare, documented only in two locations in white sand forest areas dominated by Dicymbe and Aldina (Henkel et al. 2012; Vasco-Palacios et al. 2018). In contrast, this species is the most abundant element in the monodominant forests of D. corymbosa in the Pacaraima Mountains of Guyana (Henkel et al. 2012).
Leguminous plant species, primarily those found in the genera Dicymbe and Aldina, are hosts to a variety of fungi (Smit et al. 2011, Henkel et al. 2012; Vasco-Palacios et al. 2018); however, the factors favoring the predominance of a specific type of fungus are not yet known. Therefore, a deeper understanding of life strategies, ecology, population size, and the occurrence of gene flow among populations throughout the Amazon region will enable a more robust understanding of the distribution patterns and population dynamics of C. sprucei.
Regarding threats, it is essential to understand the impact of climate change, especially the increasing temperatures and dry periods, as historically, the Guyanese populations of C. sprucei have experienced a consistent rainfall regime throughout the year (Henkel et al. 2012). Similarly, it is necessary to assess the potential impact of tourism activities in the Pacaraima Mountains, an area identified as an important center of diversity for neotropical ectomycorrhizal fungi (Smit et al. 2011; Henkel et al. 2012), yet not comprehended by government protection actions. Therefore, the key research needs are related to population size and trends, ecology, habitat and life history, use and trade, and the threats faced by C. sprucei.
The bibliography regarding the use and trade of C. sprucei is still limited; however, reports indicate that this species does not possess distinct odor and taste (Henkel et al., 2011). Furthermore, there is an increasing appreciation of species belonging to the Clavulina genus as a food resource in various parts of the world (Chang & Lee, 2010; Duhem & Buyck, 2007; Garibay-orijel et al., 2020; Khaund & Joshi, 2013), notably among the Patamona Amerindians in the Pacaraima Mountains region, where the highest record of C. sprucei is found (Henkel et al., 2004).