Absidia urquhartii A. Idnurm, 2025

Idnurm, Alexander, 2025, Absidia urquhartii (Mucoromycota) is a new species that is prevalent in Victoria, Australia, Phytotaxa 687 (1), pp. 1-8 : 4-5

Absidia urquhartii A. Idnurm , sp. nov. ( Fig. 1 )

MycoBank:—MB 854137

Etymology:—the epithet urquhartii is in acknowledgement of the contributions of Andrew S. Urquhart in the pursuit of discovery of fungal biodiversity in Australia.

Holotype:— AUSTRALIA, Victoria, MELU F155166 a preserved in the University of Melbourne Herbarium on Whatman filter paper and contains mycelium, sporangia and asexual spores.

Ex-type strains:—UoMD23-19 (University of Melbourne) = JMRC:SF015714 (Jena Microbial Resource Collection).

GenBank numbers:— ITS PP973115; two copies of LSU PP973118 and PP973119; genome sequencing reads PRJNA1117230.

Description:—Asexual morph: radial growth rate on PDA 9 mm per day at 22 °C, 5 mm per day at 30 °C; no growth at 37 °C. Colonies olive grey front side, greenish grey from the obverse of the plate. Asexual spore production is from sporangia, with the sporangiophores producing 3–4 branches. One branch elongates without the differentiation into sporangia, and that generates another whorl of sporangia-forming structures. Additional sporangiophores are produced laterally. Sporangiophores are up to 10 mm in height. Sporangia are globose, multi-spored, and increase in size and level of dark brown pigmentation depending on developmental age. Columellae are pear-shaped with prominent apophyses and collars at their base, and below the collars clearly-defined septa. Columellae (n = 9) of width 19.35–28.46 µm (average 23.51 µm), length from tip to the septa, 42.26–51.66 µm (average 47.46 µm) and diameter of sporangiophore at the septa 6.22–10.17 µm (average 8.18 µm). Sporangiospores are globose, hyaline and smooth, and (n = 32) 3.12–5.29 µm (average 3.78 µm) in diameter.

Sexual morph: no production of zygospores when grown in isolation, and DNA sequence analysis supports a heterothallic life cycle. When crossed (e.g. UoMD22-19 × UoMAU377), zygospores form that range in size during development up to ~110 µm. Gametangia are elongated and of equal size. One set of suspensor cells produces appendages that surround the zygospore.

Material examined:—single-spored in vitro culture for strain UoMD23-19 isolated from an environmental sample, collected on 17 September 2023, in the Brisbane Ranges National Park.

Additional specimens examined:— AUSTRALIA. Victoria: 27 Oct. 2018, Urquhart (UoMAU372) ; 19 May 2018, Urquhart (UoMAU373); 19 Oct. 2018, Urquhart (UoMAU377).

Habitat:—Isolated from leaf litter in Victoria, Australia.

Notes:—The asexual spore and zygospore properties of Absidia urquhartii are consistent with other members in the genus. The basis for describing this as a new species is: i) the differences it shows in DNA sequences of diagnostic regions relative to other members in the genus, ii) the reproductive isolation from one of its closest relatives and iii) morphological differences. Based on the phylogenetic analyses, the four species that A. urquhartii is most closest related to are A. glauca , A. globospora , A. sympodialis and A. virescens . Morphologically it is distinct from all four. Absidia glauca produces more and longer appendages around its zygospores compared to A. urquhartii ; furthermore, A. glauca produces unequally-sized suspensor cells while those of A. urquhartii are equally-sized. The columellae of A. urquhartii have pronounced apophyses and collars, which are either not or are inconsistently observed in A. globospora and A. sympodialis . Likewise, collars are rarely or sparsely observed for A. virescens . The sporangiospores of A. virescens vary from globose to subglobose and are of a wider range of sizes than A. urquhartii . Furthermore, A. globospora cannot grow above 30 °C whereas A. urquhartii can.

Figures

FIGURE 1. Features of Absidia urquhartii sp. nov., strain UoMD23-19. A. Photograph of the site from where the type of the species was obtained. B. Culture on a PDA 9 cm diameter plate grown for 4 days at 22 °C from above, and C. Obverse of culture plate. D. Whorl of three sporangiophores terminating in sporangia. E. Columella. F.Asexual spores. G. Zygospore from a UoMD23-19 × UoMAU377 cross. H. Zygospore from a cross between two A. glauca strains. Scale bars: E, F = 10 µm, D, G–H = 100 µm.