Climacodon sanguineus belongs to the family Meruliaceae, order Polyporales in the phylum Basidiomycota. The genus Climacodon was first introduced by Petter Karsten, a Finnish mycologist in 1881. The genus name, meaning “ladder teeth”, is derived from the Latin words climac and odon which means ladder and teeth, respectively. Climacodon is a hydnoid or toothed fungus where the hymenium (spore-bearing surface) on the underside of the cap takes the form of teeth instead of gills or pores. This genus has variable coloured basidiocarps or fruiting bodies ranging from white, cream to buff, rose pink, red and dark red brown with a monomitic hyphal system (consisting of only generative hyphae) and clamp connections (Maas Geesteranus, 1971; 1974).

Seven species of the genus Climacodon have been recorded worldwide (Index Fungorum, 2020). In Malaysia, three species are known, namely, C. dubitativus (Lloyd) Ryvarden, C. pulcherrimus (Berk. & M.A. Curtis) Nikol. and C. roseomaculatus (Henn. & E. Nyman) Jülich (Mass Geesteranus, 1971), with one unidentified, possibly new species (Zainuddin et al., 2010). Climacodon sanguineus is the fourth species of Climacodon reported from Malaysia and represents a new record for the country. Previously this species was called Hydnum sanguineum and then Donkia sanguinea before it was renamed C. sanguineus by Maas Geesteranus (1971).

Specimens of Climacodon were collected during expeditions to Cameron Highlands in 2007, 2010 and during a recent field study in January 2020 under the Cameron Highlands Montane Park (CHiMP) project. The fungus was found growing solitarily or in small groups on woody substrates such as twigs and branches. The DNA sequence of the most recently collected Climacodon specimen was matched against the National Center for Biotechnology Information (NCBI) database and it showed high similarity of 96% with the species C. sanguineus studied by Moreno et al. (2017). The phylogenetic analyses by Moreno et al. (2017) showed that C. sanguineus forms a well-supported clade with C. septentrionalis, the type species of Climacodon. Climacodon sanguineus has been reported in tropical forests of Central Africa, such as Congo (Beeli, 1926) and Gabon (Moreno et al., 2017), and seems to be confined to tropical regions only.

Climacodon sanguineus is recognised by its scarlet red colour and velvety cap, with coral to salmon coloured spines or teeth-like protrusions on the underside of the cap. The cap is 15-75 mm wide and the spines 1-3 mm long, extending down the stipe or stem. The stipe is up to 10 mm long and 4-7 mm wide. The name of the species originates from sanguis, the Latin word for “blood”, in reference to the red colour of the cap. Some species of Climacodon are saprophytes, for example, C. pulcherrimus (Moreno et al., 2007) while some are plant pathogens, such as C. septentrionalis which causes wood decay (Koski-Kotiranta & Niemela, 1987). There is, however, limited information about the ecological roles of C. sanguineus in the forest.

Among the species of Climacodon, C. sanguineus resembles C. roseomaculatus which has similar cap colour, hymenophore and spore shape. However, C. roseomaculatus has an effused-reflexed (flattened fruiting body with the edge rise from the substrate forming a shelf-like structure) or sessile (attached directly to the substrate) pileus with narrow base, and rarely has a stipe compared to C. sanguineus, which has one (Mass Geesteranus, 1971). The DNA sequence of our Climacodon specimen was also matched against the NCBI database and it only showed 91% similarity with the species C. roseomaculatus. Climacodon sanguineus has so far only been encountered at Cameron Highlands at altitudes ranging from 1400 m to 1600 m above sea level (a.s.l) while C. roseomaculatus was reported in Mount Kinabalu at an elevation of between 1500 m and 1700 m a.s.l., implying that these two species are distributed in high altitude tropical forests.

Presently, C. sanguineus has only been found in one locality in Malaysia, restricted to highland forest in Cameron Highlands. Apart from C. roseomaculatus which is also found in highland forest, other species of Climacodon in Malaysia such as C. dubitativus are widely distributed and have been collected from several localities of lowland forests at Pasoh, Negeri Sembilan and Tembeling, Pahang (Mass Geesteranus, 1971; Ryvarden, 1992). Another species, C. pulcherrimus was reportedly found in different localities such as Mawai in Johor, Tembeling, Sungai Cheka and Fraser’s Hill in Pahang (Mass Geesteranus, 1971). Climacodon sanguineus has not yet been assessed for the IUCN Red List although a study by Moreno et al. (2017) reported this fungus as an extremely rare species. Thus, it is crucial that further studies be conducted on this species and its conservation status assessed.