Myxomycota dictionary

In the following is explained some special terms often used in connection with Myxomycota. The list is by no means exhaustive and will be expanded as needed.

Aethalium
Type of myxomycete fruitbody. Aethalia are spherical to cushion-shaped. The size varies from a few mm to several dm in diameter. Examples are the common species Lycogala epidendrum and Fuligo septica. The largest aethalium is probably attained by Brefeldia maxima, where it may totally cover large tree-stumps.
Capillitium
Sterile elements within the fructification of the Myxomycetes. The capillitium may take the form of solid threads or hollow tubes, be simple or branched and then often forming an extensive network. The true capillitium is developed among the spores within the sporocarp or plasmodiocarp. In many species, particularly those with larger fructifications, aethalia and pseudoaethalia, similar sterile elements, the pseudocapillitium, are often found. In these species the pseudocapillitium is usually interpreted as remnants of the common walls of the individual sporocarps constituting the fructification.

A capillitium is present in the majority of species of Myxomycetes. In a few genera however, f.ex. Licea, no such element is found. One may speculate whether this is a 'primary' character or it is the result of a secondary reduction. In any way, the absence of capillitium is presently considered an important character of the genus Licea.

The specific development of the capillitium plays an important role in the generic taxonomy of the Myxomycetes. A capillitium of solid threads is found in f.ex. the genera Comatricha, Stemonitis, Didymium and Diderma. Hollow tubes is found in f.ex. Arcyria, Hemitrichia and Physarum. A particular type of tubes is the elaters. These are relatively short segments of tubes, pointed in both ends and lying free in the sporemass of species of Trichia. The surface of the capillitial elements may be almost smooth, but more often they are decorated with an intricate ornamentation of warts, spines, or spiral lines.

The function of the capillitium is mostly associated with the dispersal of the spores. A 'classical' example of this association involves the genus Stemonitis, where the capillitium in connection with a fine surface net make the sporocarp act as pepper-pot, securing a gradual dispersal of the spores when the sporocarp is moved by the wind. Another example is the elaters of Trichia species.

Elater
Special development of the capillitium found in the genus Trichia and Oligonema. The elaters consist of hollow tubes, often with ± extended, pointed ends and lying free among the spores. As the other hollow types of capillitium, the elaters develop witin vacuoles of the plasma mass of the maturing sporocarp. The elaters bear an ornamentation of ± well developed spiral lines or faint warts. The lines may be smooth or additionally decorated with spines.

The spiral ornamentation makes the elaters twist with sudden jerks as the moisture of the ambient air changes, and thus virtually throwing away spores from the sporocarp. The mechanism is easily seen when sporocarps are inspected with the stereo microscope and the fructification is dried out by the heat from the lamp.

Peridium
The membrane covering the spore container. The peridium originate in the plasmamembrane which surrounds the plasmodium and immature sporocarps. In mature sporocarps the peridium may be thin and membraneous as in the genus Lamproderma, or if granular matter has been trapped in the external layer of mucus, it may be rather tough as is seen in the Trichia species around T. botrytis.

In the Stemonitales the peridium often disappears completely at maturity (Comatricha and Stemonitis) or leaves a tiny collar at the base of the spore container (Macbrideola).

During the maturation of sporocarps in the Physarales lime is excreted on the surface of the peridium. The lime may be granular (the genera in Physaraceae), crystalline (Didymiaceae) or as flattened plates (the genus Lepidoderma). Granular and crystalline line may be agglutinated to form an egg-shell like covering on the surface of the peridium (e.g. the genera Didymium and Diderma). In most texts on Myxomycetes such a shell is considered as being part of the peridium, in which cases the peridium may be two- or even three layered.

Plasmodiocarp
Type of myxomycete fruitbody. Plasmodiocarps are elongated, ± sausage-shaped fruitbodies, which are formed along the plasmodial veins. In cross section the plasmodiocarp may be laterally or vertically compressed. They are often branched and may form an extensive network as is seen in Hemitrichia serpula.
Pseudoaethalium
Type of myxomycete fruitbody. The pseudoaethalium is believed to originate in closely appressed, individual sporocarps, ± melted together with the common wall partly or completely dissolved. The form may vary from a flattened, cushion shape to an upright, stipitate aggregation of tubes. The individual sporocarps may be clearly discernible from the outside, as in the Tubifera species, or only visible as a faint, hexagonal pattern on the surface of the fruitbody, as in Dictydiaethalium plumbeum.
Sporocarp
Type of myxomycete fruitbody. The sporocarp is generally considered the 'basic' type of Myxomycete fructification from which the other types are developed.

Sporocarps may be globose, ± pear shaped, or cylindric in shape, sessile or stipitate.