Skierkaceae (Arthur) Aime & McTaggart, fam. & stat. nov.
MycoBank number: MB 836629; Index Fungorum number: IF 836629; Facesoffungi number: FoF;
Basionym: Skierkatae Arthur, North American Flora 7(10): 704. 1926.
Type genus: Skierka Racib., Parasit. Alg. Pilze Javas (Jakarta) 2: 30. 1900.
Diagnosis: Differs from all other rust fungi in that sporothalli sori are deep-seated and subepidermal with mature uredinio- and teliospores single-celled and non-catenulate, these forced through a narrow sorus opening by the production of new spores from sporogenous cells from which they are detached before extrusion.
Description: With the characteristics of Skierka as described and illustrated in Mains (1939b). Spermogonia deep-seated with convex hymenium, subepidermal, periphysate; aecia and uredinia uredo-type; teliospores strongly adherent, extruded in hair-like columns, germination external, without dormancy. Autoecious and macrocyclic.
Included genus: Skierka.
Host families: Burseraceae, Euphorbiaceae, Sapindaceae.
Notes: Skierka species are tropical and autoecious (Mains 1939c, Cummins & Hiratsuka 2003). All sori are subepidermal and deep-seated; non-catenulate teliospores are extruded in hair-like columns. Skierka has long held an isolated placement within Pucciniales. Arthur (1907–1931) and Dietel (1928) placed Skierka in a separate subfamily or tribe, respectively, in the Pucciniaceae; Cummins & Hiratsuka (2003) treat it as incertae sedis within the rusts. Mains (1939c) hypothesised that Skierka represented an intermediate taxon between the Melampsoraceae and Pucciniaceae (equivalent to the subordinal ranks Melampsorineae and Raveneliineae/Uredinineae, under the present classification), a position largely congruent with our placement (Fig. 1).
Fig. 1. Pucciniales. Phylogram obtained from BEAST constrained to a ML topology from three concatenated loci (28S, 18S, and CO3). The tree is rooted with Eocronartium muscicola. Families are indicated by coloured blocks; dashed lines indicate uncertainty at the referenced nodes. Genera represented by types are indicated in bold; genera represented by type proxies (as explained in methods) are indicated by *. Support for nodes is provided from an approximate likelihood ratio test (≥ 0.90), ultrafast bootstraps (≥ 95 %) and genealogical concordance factors for the three loci at each node as aLRT/UFBoot/gCF.