Abstract
Members of Xylariaceae (Ascomycota) are recognized and classified mainly on the morphological features of their sexual state. In a number of genera high morphological variation of stromatal characters has made confident recognition of generic and specific boundaries difficult. There are, however, a range of microscopical characteristics which can in most cases make distinctions, especially at generic level, even in the absence of molecular data. These include details of the apical apparatus in the ascus (e.g. disc-shaped, inverted hat-shaped, rhomboid, composed of rings, amyloid, non-amyloid); position and length of the germ slit; and presence and type of ascospore wall ornamentation as seen by scanning electron microscopy (SEM). Unfortunately many of the classical studies on xylariaceous genera omitted these features and were undertaken long before the development of scanning electron microscopy. More recent studies have, however, demonstrated their value as diagnostic characters in the family. Camillea is for example, instantly recognizable by its rhomboid or diamond shaped apical apparatus, and the distinctive inverted hat or urniform type is usually prominent in Xylaria, Rosellinia, Kretzschmaria, and Nemania. At least six categories of apical apparatus based on shape and size can be recognized. Ascospore ornamentation as seen by SEM has been exceptionally useful and provided the basis for separating Camillea from Biscogniauxia and other xylariaceous genera.
Highlights
Xylariaceae is one of the best-known and widely distributed families of Ascomycota
Squash preparations of asci and ascospores mounted in water, Melzer’s iodine reagent, and lactophenol cotton blue were microscopically examined by bright field microscopy and differential interference contrast (DIC) light microscopy with an Olympus BH2 research microscope using x10, x40 and x60 dry objectives
There are a number of taxa in which no apical apparatus can be seen by light microscopy the possibility of some remnant structures cannot be excluded as such taxa have not yet been studied by transmission electron microscopy
Summary
Xylariaceae is one of the best-known and widely distributed families of Ascomycota. The majority of the species are wood inhabitants, and are well represented in the tropics. Ju & Rogers (1996) recognized 38 genera, Whalley (1996) 40, and the number has grown to at least 76 (Lumbsch & Huhndorf 2010), the total varies according to individual opinion and the status of several genera in the family awaits confirmation. Details of the ascus, including the apical apparatus, and ascospore topography were not considered. The subsequent advent of scanning electron microscopy (SEM) has demonstrated the value of spore ornamentation and details of stromatal surfaces (Læssøe et al 1989, Whalley 1996).
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