Studying Mushrooms > Using a Microscope > Working with Ascomycetes


Using a Microscope: Working with Ascomycetes

by Michael Kuo

Microscopic analysis of Ascomycetes is a topic worthy of volumes, especially since the ascos include many, many fungi that never come across the average mushroom hunter's radar screen (yeasts, molds, tiny black dots on wood, ring worm, penicillin, and so on). Here, however, I am anticipating casual microscopic study of Morels, False Morels, Helvella species, and some Cup Fungi.


Analysis of ascospores is more or less like analysis of basidiospores, but is generally performed with unstained KOH mounts, rather than Melzer's Reagent mounts. A spore print is the best source for spores, since they are by definition mature if they come from a print. However, spores can be often found on sections of the spore-producing surface and within the asci (see below)--though spores within asci are immature, and may not have attained their full sizes. The top and middle illustrations to the right feature the elliptical ascospores of a Black Morel and the long, needle-like spores of Spathularia flavida, respectively.

Ascospores mounted in KOH sometimes feature "oil droplets," and the number and disposition of the droplets can be taxonomically important. Some spores feature two large oil droplets, one at either end; these are labeled "biguttulate." "Multiguttulate" spores feature many small oil droplets. The spores of Gyromitra korfii, illustrated bottom-right, have a large, central oil droplet and a cluster of smaller droplets on either side. The knob-like ends of the Gyromitra korfii spores are also a character that helps to identify the species.




To create a section of an asco's spore-bearing surface, simply slice a very tiny, paper-thin piece from the surface (use a very sharp razor blade). If you are working with a morel, be sure to slice from the surface of a pit, rather than a ridge, since the ridges are sterile and do not feature asci. Place the section on a slide, add a drop or two of 2% KOH, and press the cover slip down with a pencil eraser, spreading things out and creating a "crush mount." Under the microscope, note the size of the asci (length and width), and count the number of spores per ascus.

If you are working with a cup fungus, you may want to create a second mount, using Melzer's Reagent, since the tips of some asci (for example, in Peziza) turn blue in Melzer's, and the reaction (or lack of reaction) can save lots of time in the identification process.




"Paraphyses" are cells that are lined up with the asci on the spore-bearing surface, roughly comparable to "basidioles" in the basidiomycetes. However, unlike basidioles, paraphyses are often taxonomically important, so you should note their shapes and sizes. The illustration to the right features the distinctive "hooked" paraphyses of Otidea onotica.


Hooked paraphyses

Cite this page as:

Kuo, M. (2006, February). Using a microscope: Working with Ascomycetes. Retrieved from the MushroomExpert.Com Web site:

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