Physarum bitectum G. Lister, 1911

Moreno, G., Castillo, A. & Thüs, H., 2024, Critical revision of Physarales and Reticulariales (Myxomycetes) at the Natural History Museum London (BM), Phytotaxa 644 (2), pp. 79-101 : 97

Physarum bitectum G. Lister , in Lister (1911: 78)

Lectotype (designated by Lado & Wrigley de Basanta 2018): UNITED KINGDOM. England: Bedfordshire , Flitwick , 52.0038ºN 0.4965ºW, Nov 1893, C. Crouch, B.M. 1251 [ BM001089852 !], + two slides, one dry mount L:B.M.34, engraved 116 [ BM001089948 !], and B.M. 2, [ BM001247133 !]. Studied syntypes:— PORTUGAL. Near Lisbon, 38º43’N 9º09’W, Dec 1907, C. Torrend, B.M. 2298 [ BM001089848 !]. U.S.A. Washington state, 1900, J. Jackol #91, #96, #147, B.M. 2299 [ BM001089849 !] .

The collection B.M. 2299 consists of three subsamples with separate numbers (#91, #96, #147). Due to the small number of complete sporocarps in the studied syntype collections, we only sampled a small quantity for the study of sporal ornamentation.

Under SEM specimen B.M. 2298 shows spores with densely and evenly distributed baculae which are 9.0–9.5 µm in diam. In specimen B.M. 2299 the spore ornamentation in SEM is formed by abundant, low and wide baculae with an irregularly distributed warty appearance, they sometimes coalesce into short ridges, and are 8.0–7.5 µm in diam. Although there appears to be significant variation among the studied syntypes, no data on these characters are available yet for the lectotype (B.M. 1251) designated by Lado & Wrigley de Basanta (2018), and the taxonomic relevance of these differences needs to be explored further, ideally by including fresh material and molecular markers.

Currently this species is characterised by pulvinate sporocarps or elongate plasmodiocarps that are rounded and not laterally compressed. Physarum bitectum is often confused with P. bivalve , but the latter has more elongated plasmodiocarps, which are laterally compressed. In P. bitectum the internal layer is violaceous brown and shows irregular and apical dehiscence, while in P. bivalve the internal layer of the peridium is colourless and the dehiscence is a longitudinal fissure. A study comparing these two species and the new P. clavisporum which is separated by the shape of its spore ornamentation was carried out by Moreno et al. (2009).

Lister (1911) introduced the new name Physarum bitectum although he regarded it similar to Physarum diderma Rostaf. and pointed out the difficulty of correctly interpreting P. diderma in the absence of Rostafinsky’s type material. We follow, for this latter species, the concepts of Harling (1952) and Martin & Alexopoulos (1969).