Nummularia Tul. & C. Tul. was
erected in 1863 by the Tulasne brothers on a suite of characters that has been used to the
present time to distinguish these fungi from their kin (Tulasne and Tulasne, 1863). Nummularia
is particularly descriptive of many of these fungi which, in fact, have flattened,
disc-shaped stromata reminiscent of coins. Unfortunately, Nummularia Tul.
& C. Tul. is a later homonym of Nummularia Hill, a genus of the
angiospermous Primulaceae. The nondescriptive name, Biscogniauxia Kuntze,
was adopted for the genus (Pouzar, 1979). In any case, the Tulasne brothers understood Biscogniauxia
[as Nummularia] extremely well and, indeed, their observations on stromatal
development have not been improved upon in 133 years!
Most mycologists accepted the Tulasne concept of Biscogniauxia and numerous additional species were described. Curiously, a great student of the Xylariaceae, J. H. Miller, moved most of the applanate species of Biscogniauxia [as Nummularia] to section Applanata of Hypoxylon (Miller, 1961). In doing so, he apparently chose to diminish the importance of developmental differences between Biscogniauxia and Hypoxylon. His section Applanata thus contains taxa of Camillea Fr., Jumillera J. D. Rogers, Y.-M. Ju, & San Martín, Whalleya J. D. Rogers, Y.-M. Ju, & San Martín, as well as Biscogniauxia (Laessře, 1994; Rogers et al., 1997). Martin (1969b) presented an expanded concept of Biscogniauxia [as Numulariola House] that included taxa of Camillea, Camarops P. Karst., Peridoxylon Shear, and Bolinia Nitschke, and others. This concept is considered untenable by most modern workers.
In this treatment Biscogniauxia embraces fungi with the following characteristics:
1. Bipartite stroma, the outer layer of which dehisces or disintegrates to expose the ascoma-bearing part below. The former layer often is sloughed along with overlying bark.
2. Stout conidiophores that are usually Periconiella-like in morphology and, in nature, are borne between the dehiscing and underlying stromatal layers. Conidia are dry.
3. Internal carbonaceous, or in several cases noncarbonaceous, locules that bear individual papyraceous perithecia. Stromata with mature perithecia usually lack white tissue either between or beneath perithecia.
4. Stromata that do not release colored pigment in KOH.
5. Ascospores that are usually dark in color and usually feature a conspicuous germination slit. In the case of taxa with ascospores bearing a hyaline appendage cell, the darker part bears a germination slit.
6. Ascospores that are essentially nonornamented. Two taxa have striate ascospores, one has ribbed ascospores, and one has reticulate ascospores (see later).
7. Asci with short stipes (as compared with the spore-bearing part) and an iodine-positive apical ascus ring that is broader than high. Rings of some species stain light blue toward the apex and darker blue below.
Biscogniauxia species are probably, without exception, bark parasites. They develop within the bark and forces produced between the inner and outer stromatal layers, and the raised rims of some taxa, break the overlying bark. Wood beneath the bark is decayed to some extent, the decay being a physiological white rot, i.e., both cellulose and lignin are degraded. Sacs composed of darkened hyphae are sometimes formed and cuts through them appear as delicate brownish or blackish lines, so-called zone lines.