GENERIC AFFINITIES AND EVOLUTION
The genera most closely allied to Daldinia
appear to be Hypoxylon and Entonaema. It is conceptually easy to derive Daldinia
from Hypoxylon by development of a zonate ring structure in the stroma of
the former. This might have come about under the selective influence of dry environments
on capacity for stromatal water storage. As discussed earlier herein, if rings truly
represent, in part, abortive attempts to form perithecia, then regular abortion in favor
of rings was probably selected, i.e., because of the presumed value of rings in storing
water. Entonaema stores liquid water under pressure. The water presumably
fills an expanding cavity with gel-lined walls. It seems possible that Entonaema
has dispensed with rings altogether, using turgor pressure generated by gels to both
expand the stroma and store water.
The relationships among Daldinia, Hypoxylon, and Entonaema are indicated by pigmented stromata, by Nodulisporium type anamorphs, by ascus ring morphology (broader than high), and by ascospore germ slit placement on the convex side of the ascospore (see Rogers, 1982). The presence of naphthalene compounds in Daldinia and Entonaema further indicate a close relationship (Whalley and Edwards, 1995).
Laessře (1994) has reflected the views of various workers in suggesting that Daldinia should be merged with Hypoxylon. Although these genera are undoubtedly closely related, their lifestyles seem somewhat different (see earlier herein). We believe that the biology of these genera should be taken into strong account in taxonomic matters.
Another genus with possible affinities with Daldinia is Rhopalostroma D. Hawksw. The stipitate stromata bearing perithecia beneath an outer crust, ascospore morphology, and robust Nodulisporium anamorph (proven in one species) (Hawksworth, 1977; Hawksworth and Whalley, 1985) are suggestive of Daldinia. The interior flesh, however, lacks distinct rings and asci lack an apical ring, usually deliquescing and presumably lacking the capacity to forcibly discharge ascospores (Hawksworth, 1977; Hawksworth and Whalley, 1985). It is probable that this African-Asian genus developed from a Hypoxylon-like ancestor and is going the direction of cleistocarpy. That is, the deliquescing asci and the friable perithecial layer of some Rhopalostroma species suggest that, in addition to ascospores passively discharged from ostioles during wetting, ascospores might be exposed during ascomatal disintegration and wind-disseminated. This is reminiscent of Pulveria Malloch & Rogerson [= Pyrenomyxa Morg.] and Phylacia Lév., cleistocarpous genera that have lost both the perithecial ostioles and forcible ascospore discharge. As Hawksworth (1977) pointed out, Rhopalostroma asci also have a certain resemblance to those of Thamnomyces Ehrenb.