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Using a Microscope: Clamp Connections

by Michael Kuo

Rolf Singer's 1956 key to Pluteus worldwide uses the presence or absence of "clamp connections" to break up the genus and sort out dozens of species. Singer (as many readers already know) was a mycological giant of the 20th Century, and his description of Pluteus fuliginosus, based on careful study of the original "type collection" made by Murrill 40 years earlier, says: "all hyphae without clamp connexions" (164).

Now, this is Rolf Singer we're talking about, studying a type collection. Two years later, however, Alexander Smith and Daniel Stuntz (also giants in the world of mycology) published these lines in their study of Murrill's original Pluteus fuligineus collection:

    We found one recognizable clamp connection as the result of an hour's search, which in itself may not mean much, but it does establish their presence. When the difficulty of establishing this character on dried material, such as type specimens, is considered, however, our observation may have considerable significance, for it may be that in the study of fresh material clamps can be rather easily demonstrated. Consequently we hesitate to recognize as authentic the identification by Singer of specimens which he placed here but which were collected on other substrata, and presumably lacked clamps (122).

There are several elements of this little myco-drama that might make for good discussion, but the thing I want to point out is that Alexander Smith and Daniel Stuntz found "one recognizable clamp connection as the result of an hour's search." Now, finding clamp connections is not always so difficult that it takes experienced mycologists hours to do it--but it is not easy, either, and one might reasonably decide there are better things to do with one's time. How's your lawn looking these days?

A clamp connection is a connection between two fungal cells. Rather than merely terminating with a simple dividing wall, clamped cells involve a little arm, or clamp, that reaches from one cell to the next, appearing to hold the cells together. Some mushrooms have clamp connections; others don't. Determining whether clamp connections are present in your mushroom will certainly help you make progress through many traditional, microscope-based identification keys. But it must be pointed out that recent DNA research has called into question the whole idea of whether clamp connections are actually "informative" characters. Cantharellus and Craterellus, for example, used to be sorted out on the basis of clamp connections--but DNA has shown us that our arrangements of these genera based on clamps did not provide an accurate picture of what is related to what, and that clamps, in fact, don't seem to have any correlation to genetic developments.

Clamp Connection

The difficulty in viewing clamp connections comes with the fact that you must be able to see single strings of cells clearly in order to see how the cells are connected. This means making a "crush mount," and pressing pretty darned hard in order to get the tissues to separate on the slide. Clamps, when present, are sometimes limited to certain areas (for example, the bases of some basidia are clamped) and you will need to rely on each identification key to figure out whether you should search for clamp connections in a particular place, or anywhere within the mushroom's tissues. Be prepared to search for a long time, and to be disappointed. Many times I have searched long and hard for clamp connections in mushrooms I knew must have them, since I had already identified them with certainty through other features . . . and come away empty-handed.

Cite this page as:

Kuo, M. (2006, February). Using a microscope: Clamp connections. Retrieved from the MushroomExpert.Com Web site:

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