What are Lycogala confusum and L. exiguum? Revising authentic collections of myxomycetes in the light of a molecular-aided species concept

The myxomycete species Lycogala exiguum and L. confusum were formally described by A.P. Morgan and N.E. Nannenga-Bremekamp ex Ing in 1893 and 1999. We here present a critical analysis of authentic material of these species using a recently developed species concept. N.E. Nannenga-Bremekamp's collections of Lycogala confusum (herbarium BR) consist of well-preserved fruiting bodies and slide mounts, as well as detailed collector's labels. Accessions NENB1869, 2010 and 4950 display a very similar morphology, including the size of fruiting bodies, peridial vesicles and spores. We assign these collections to L. confusum according to the novel, narrower concept of the species. Specimen NENB10977 differs from the rest of collections in the peridium morphology. Specimen NENB11008, after comparison with modern collections, was assigned to the newly described species L. maculatum. A critical analysis of A.P. Morgan's material of L. exiguum (herbarium BPI) showed perfectly preserved fruiting bodies and one collector's slide mount. Labels located on the inner surface of the boxes we attribute to A.P. Morgan. The authorship of the outer labels remains mainly unknown, but the label on the specimen BPI834633, as well as the notes on the labels BPI834630, 834632 and 834633, can be traced back to G.W. Martin. Accessions BPI834630 (containing fruiting bodies) and 834633 (containing a slide) are marked by G.W. Martin as lectotypes. These samples are morphologically homogeneous and can serve as a good standard for the species. Accessions BPI834632 and 834700 contain, in addition to L. exiguum, also fruiting bodies of other species. We identify the additional material in the specimen BPI834700 as L. maculatum, and one in BPI834632 as a probably undescribed species of the genus Lycogala, or a deviant exemplar of L. exiguum. In the old slide preparations oil depositions in peridial vesicles which are typical for fresh material seem to have vanished, and this makes the contours of the vesicles much more visible than in recently made preparations.