The Capillitium and Columella
Estimated Time: 20–30 minutes
Course: Myxomycetes 201 — Field Recognition and Morphological Diversity
Lesson Type: Reading + Morphological Analysis (self-paced)
1. Internal Architecture of Myxomycetes
While fruiting body shape is important for field identification, many myxomycetes also possess complex internal structures that aid in spore dispersal and species recognition. Two of the most important structures are the capillitium and the columella. These structures become increasingly important in advanced identification and taxonomy, bridging the gap between field observation and microscopy.
Key Takeaway: The capillitium and columella are critical structural features used in identifying major groups of myxomycetes and understanding how spores are dispersed.
2. What Is the Capillitium?
The capillitium is a network of sterile fibers or threads located inside the fruiting body among the spores.
These threads help regulate how spores are released into the environment. In many species, the capillitium responds to humidity changes, flexing and moving as the air dries or becomes moist. Capillitium structure is one of the most important taxonomic characters in myxomycete identification.
Functions of the Capillitium
- Supports and separates spores
- Improves gradual spore dispersal
- Responds to humidity changes
- Provides structural stability inside sporocarps
Did You Know? In some species, capillitium threads twist and flex in response to changing moisture levels, helping spores disperse over time instead of all at once.
3. Major Types of Capillitium
Elastic Capillitium
Species in the order Trichiales often possess brightly colored, elastic capillitium threads with spirals or ornamentation.
- Flexible and spring-like
- Often brightly pigmented
- May contain spiral bands
- Common in Arcyria and Trichia
Examples: Metatricha vesparia
Elastic capillitium threads in Metatrichia vesparia
Netted Capillitium
Some species form highly interconnected capillitium networks that create mesh-like internal structures.
- Complex branching networks
- Improves spore retention and release
- Common in Stemonitis and related genera
Field Clue: Mature sporocarps may appear fibrous or hairy after the peridium breaks open.
Comatricha ellae, found in Awosting Reserve, NY showing netted capillitium exposed after peridium rupture.
Lime-Containing Capillitium
Species within the order Physarales frequently contain lime deposits associated with the capillitium.
- White or chalky appearance
- Contains calcium carbonate deposits
- May form lime nodes
- Important diagnostic feature
Examples: Craterium, Physarum
4. What Is the Columella?
The columella is a sterile internal support structure extending upward into the fruiting body from the stalk.
Not all myxomycetes possess a columella, but when present, it can be an important diagnostic feature. The columella helps support the spore mass and capillitium, particularly in tall sporocarps.
Characteristics of the Columella
- May extend partially or fully through the sporotheca
- Often dark and rigid
- Supports capillitium attachment
- Especially common in Stemonitis and related taxa
Field Clue: In broken sporocarps, the columella may appear as a dark central column.
5. Capillitium and Columella in Taxonomy
Modern myxomycete taxonomy relies heavily on microscopic and structural characteristics, especially:
- Capillitium branching patterns
- Thread ornamentation
- Lime deposition
- Presence or absence of a columella
- Attachment points and network arrangement
These features are often essential for distinguishing visually similar species.
| Order | Capillitium Characteristics | Columella Presence |
|---|---|---|
| Trichiales | Well-developed, free or sparsely connected threads; often brightly colored; usually ornamented with spirals, rings, spines, or bands; lime absent | Usually absent |
| Stemonitidales | Dark, highly branched network attached to a central axis; forms intricate internal meshes; lime absent | Usually present and prominent |
| Physarales | Threads often incorporate lime nodes, lime deposits, or lime tubes; may be white, yellow, or chalky; network variable among genera | Variable |
| Liceales | Capillitium reduced, sparse, rudimentary, or completely absent; some genera possess pseudocapillitium instead | Typically absent |
6. Observing Internal Structures in the Field
Although microscopy provides the best view of these structures, many capillitium and columella characteristics can still be recognized macroscopically.
- Use a 10x–20x hand lens
- Observe mature fruiting bodies
- Look for exposed internal fibers
- Examine broken sporocarps carefully
- Note texture after the peridium ruptures
Photography combined with magnification can reveal remarkable structural detail even before microscopic examination.
Field Observation Tip: Older sporocarps often expose capillitium more clearly after weathering removes the outer peridium.
7. Common Species Demonstrating Internal Structures
- Stemonitis axifera — prominent columella and fibrous capillitium
- Arcyria cinerea — elastic capillitium
- Trichia varia — ornamented capillitium threads
- Didymium squamulosum — lime-containing structures
- Physarum viride — lime nodes within capillitium
8. Lesson Summary
The capillitium and columella are among the most important internal structures in myxomycetes. These features play major roles in spore dispersal, structural support, and taxonomic identification. By learning to recognize capillitium texture, branching, elasticity, lime deposition, and columella presence, students develop foundational skills necessary for advanced microscopy and species-level identification.
Next Lesson: Field Photography and Documentation Standards