topic::
It is proposed that the lamella edge cells in Amanita are not cheilocystidia and that they are analogous to the stipe context of the Amanitaceae or to the supporting hyphae of the glutinous universal veil on the stipe in Limacella.
posted by:: R. E. Tulloss
annotation:: first draft posting
date of post:: 11 feb 2010
date last edited:: 11 feb 2010
original extended annotation:: This posting was written in response to a question from Mr. Yadwinder Singh (Research Scholar, Department of Botany, Punjabi University, Patiala-147002, Punjab, India): "What is the difference between cheilocystidia and the lamellae edge cells present in the genus Amanita?  Both are sterile cells; both are present at the 'knife edges' of gills."
With regard to distinguishing lamella edge cells from cheilocystidia, I think there are several points that are very important.
I. First, consider the evolutionary history of Amanita.  Morphological and Molecular Pylogenetic data agree that Amanita and Limacella had a common ancestor.  Of the two sister taxa, Limacella is (by all evidence) the older.  Morphologically the hyphae that support the gluten of the universal veil are likely to be analogous to the the chains of inflated cells of the universal veil of the basal taxa in Amanita (members of Amanita subsection Vittadiniae).  The presence of clamps in all known species of Limacella is an additional shared character between that genus and the most basal of the basal Amanita species.  There are many other interesting analogs and shared characters.  But let us focus on your issue.

The edges of the gills of Limacella are entirely fertile.  There are no known taxa of Limacella that bear any cystidia.  All recent authors (since H.V. Smith in the 1940's) have excluded taxa from Limacella when cystidia were present.  In my recent study of the genus Limacella, I could only find two (recently described) taxa that were purported to belong in Limacella and had cystidia reported; in both cases (and I am relying solely on the protologs for the moment), these taxa also have other characters suggesting that they don't belong in Limacella (for example, having large spores).  In addition, the descriptions are clearly hurried and produced by authors who seem not to be very much aware of even the mid-Twentieth Century literature on Limacella.  At any rate, current evidence strongly suggests that the ancestry of the earliest Amanitae included only taxa lacking cystidia.  This is point number one regarding evolution of Amanita.

A major stage in the development of the genus Amanita produced a significant transformation that segregates the genus (by ontogeny) from all other agarics.  Probably, in response to extended drying of the earth, the ancestry of Amanita evolved to delay expansion and sporulation to the extent that development of the basidiome can start when water is available and, at least to some degree, stop if the water disappears, and then restart development/expansion when water returns.  Among other things, bearing the basidiome's water on the exterior in a glutinous universal veil was replaced by (apparently) inflating the cells of the volva and containing water there which served as a protection against dessication.  One of the adaptations of Amanita was to grow all the usual "agaric parts" simultaneously within an enclosed space and delaying complete tissue differentiation...which gave rise eventually to the schizohymenial ontogeny of today's Amanitae.

During the hypothetical period of transformation to their current form, mechanisms developed that permitted such things as the segregation of hymenial surfaces, the segregation of gills from a partial veil or from the stipe surface.  The gill edges ceased to be fertile and the entities we call lamella edge cells developed ensuring undistruptive separation of the gills from the adjacent tissue.  Once the tissues separate, the lamella edge cells collapse and dessicate or gelatinize.  This is not cystidia-like function or "behavior."

Are there analogs of these edge cells in Limacella? What could they be?

II. Recall that Limacella is considered to completely lack cystidia, and, particularly, cheildocystidia.  Therefore, the analog of the Amanita lamella edge cell is very unlikely to be derived from a cheilocystidium in a common ancestor of Amanita and Limacella. Cheilocystidia arise from tissue lying within the subhymenium or the lamella trama in taxa where cheliocystidia are present.  However, the lamella edge cells arise from an interwoven, cable-like structure that is originally arranged PARALLEL to the similar structures of a partial veil and/or a stipe surface.

In a development process that seems very likely to be driven by the presence, absence, movement, etc. of hormonal concentration fronts (wet chemistry), it is very easy to understand how interfaces between developing tissues in a solid primoridum could develop a thin layer with a form intermediate to the two tissues such a layer separates.  In the developing stipe context, the tissue is developing longitudinally (vertically) with very strong subparallel alignment of elements.  The predominant elements are filamentous undifferentiated hyphae and inflated cells (in chains in some species, but usually single and terminal) that we call acrophysalides.  Observations of Bas and subsequent authors suggest that solitary terminal acrophysalides are a derived condition and chaings of such cells are a "primitive" condition.  While these acrophysalides can be hundreds of micrometers long in the stipe context, they are much smaller at the stipe surface only a few tens of micrometers long in the partial veil.

Considering the orientation of the tissues, we might well suppose that the stipe's acrophysalidic tissue (pre-existing in the common ancestry of both Amanita and Limacella and, indeed, a defining character state of the family Amanitaceae) may be a possible analog for the edge cells of the lamellae. Let us look at the other side of the interface.  In the normal agaric development of a Limacella, the gill edges comprise basidia and basidioles.  They are inflated cells of an appropriate size, shape, and position to be considered as possible analogs for lamella edge cells; HOWEVER, it is much more difficult to explain how basidia and their subhymenium could both be transformed to produce the present day cable-like structure densely set with chains of inflated cells. To shorten this discussion a bit (for the moment only...what is omitted must be made explicit in the future), I think it is much more apparent how the lamella edge cells and their supporting hyphal cable could be an analog of stipe context/surface (there is little difference in form of these tissue-regions) than how subhymenium and basidia could cease to have a reproductive function and become so strongly segregated from the bilateral structure of the lamellae. This point of view provides a number of reasons against considering lamella edge cells as cheilocystida. The lamella edge cells are cells of a type utterly absent in agarics that lack schizohymenial development. It seems more appropriate to consider them modified acrophysalides than to imagine that they could be cheilocystidia.

III. Another possibility that cannot yet be posed in detail (because of the very minimal anatomical information available on species of Limacella) is as follows: The analog of the lamella edge cells of Amanita is the glutin-supporting hyphae of the universal veil on the stipe in Limacella.
IV. It might be argued, the hyphal cable (from which the lamella edge cells arise) is connected to hyphae that pass into the lamella trama; and, hence, the lamella edge cells could be said to arise from the lamella trama.  On the contrary, hyphal connections interpenetrating adjacent tissues is to be expected since ALL developing tissues of the original primordium were originally intimately connected via hyphae.  Indeed, the word "schizohymenial" comes from the fact that the hyphal connections between what become opposing hymenial surfaces have to be broken for the basidiome to expand into an agaric form.  These considerations give rise to a new question: What is the structure of the interface between the stipe and the layer of tissue we call "lamella edge cells"?  One might hypothesize that it would be a "mirror image" of the arrangement on the lamella edge.  Some observations would be useful.
V. Experiment.  While Dr. Yang and I have both begun to pay greater attention to the morphology of the cell edge than was done previously, I do not think anyone has examined the morphology of the ridges of cells left on the apex of the stipe and/or on the upper surface of a membranous partial veil in many amanitas after the stipe and lamellae separate. It is commonly observed by collectors of amanitas that these ridges or "lines" on the stipe apex are positioned exactly as though they were matched to the lamellae edge during development of the basidiome. They are (reasonably) assumed to be the same tissue as the lamella edge cells by some and passed over with few (if any) words by others.  I know of no one who has looked at how these "lines" of cells are attached to the stipe surface.

I suggest that careful examination of these lines of tissue might be relevant to the question of the evolutionary origin of the lamella edge cells. I think a thorough investigation of this issue in a variety of taxa (but especially in basal taxa of Amanita), might produce results bearing strongly on the morphologically-based understanding of how evolution in Amanita has yielded the "success"" of schizohymenial development.