Curious Cladonias

I've been wanting to write about the genus Cladonia ever since I started this blog. The tiny, fairy-looking thalli are everywhere moisture may be found on the forest floors of Colorado. Cladonia species are an enchanting group of lichenised fungi that show fantastic morphological variability in their horns, tentacles, cups, antlers, and many other shapes that vary greatly both within and between species. With this in mind, all of the "identifications" I have made in this post are based on macroscopic features and are provisional at best.

Cladonia pyxidata growing on decaying pine litter on a damp forest floor near Mount Evans. Despite its pixie-ish appearance, this lichen's name actually derives from the Greek for "box"(7).

Ecology and Distribution 

Cladonia lichens can be found all over the world in climates as varied as the jungles of Thailand and the treeless expanse of the Canadian Shield(1, 2). As a rule, Cladonia live in moist sites growing on mosses, soils, or on wood(2). Some lichens in this genus, such as the Cladonia rangiferina (colloquially known as "reindeer moss), serve as a primary source of forage for large, cold-climate animals such as reindeer and caribou(2). They also help to maintain the environments they live in by providing a cool, reflective layer of insulation over the ground which prevents it from overheating in direct sun. 

Colorado has 43 species of Cladonia according to the Consortium of North American Lichen Herberia (CNALH)(3). They live virtually any place on the forest floor where moisture accumulates, seeming to favor the soft needle litter and moss under fir forests in the montane zone, but I have found them growing all the way down to the planes under gamble oaks. I have not found them growing even in consistently moist habitats in the Denver area. Some Cladonia lichens can actually tolerate ground pollution to the point where they can re-colonize slag heaps(4), so I imagine that something in Denver's air must disagree with Cladonias (and many other lichens seen in the mountains but not around town). 

Morphology and Taxonomy 

Taxonomically, the genus Cladonia falls into the family Cladoniaceae, which after a bewildering maze of finely distinguished groups lands it in the large and venerable phylum Ascomycota, the sac fungi(1). The high level of variability in Cladonia ssp. has demanded moving beyond morphology into chemistry and phylogenetic tests for the purposes of taxonomy, although even with these tools the genus still continues to vex researchers with its mercuriality(1). Essentially, our lichens in Cladonia are similar to the vast majority of lichens in being ascomycetes rather than the familiar, mushroom-forming basidiomycetes. 
     Cladonias are characterized by a curious duel-thallus: a foliose primary thallus from which erupts the much more noticeable and bizarrely-formed secondary thalli(4). (for a refresher on lichen terminology, see this previous post),  These structures which are termed "podetia" are those which catch our eye in the woods, because despite being small, there is really nothing else in the forest shaped like them. Likely due to their alien appearance, Cladonia-like shapes will occasionally crop up in works of fiction: a patch of familiar-looking cups can be seen in this screenshot from Mass Effect: Andromeda.
     Not all Cladonia podetia are splash cups, but many of the more prominent ones in Colorado serve this purpose. A splash cup serves to spread propagules via expulsion when a rain drop blasts them out by landing in the cup. Cladonia equipped with splash cups spread both isidia and haploid spores from their apothecia, which line the rim of the cups. 
     The podetia which are not splash cups may or may not bear isidia, and can assume a variety of alien forms. The adaptive significance of a fruticose secondary thallus which often outlives the foliose primary thallus is not really known. Podetia which have had their rates of photosynthesis measured via chlorophyll fluorescence consistently demonstrate elevated activity in the more elevated and more distal areas of each podetium(6).

Gallery of Colorado Cladonias

     Here are some images of the great variety of shapes seen in Cladonia lichens. To see many of these lichens for yourself, you need only inspect the decaying pine litter and logs on any North-facing slope near Denver. C. coccifera, ecmocyna, and cervicornis seem to prefer the more consistently moist environments in the montane forests at higher elevations. 

C. coccifera, the British Soldier lichen, or possibly C. carriosa (possibly derived from the same root as 'carrion' due to the color of the prominent, meat-colored apothecia)(7).

C. ecmocyna has podetia which are densely covered in foliose projections. While the common naming of  lichens is a dubious proposition at best, this one is ostensibly known as the frosted Cladonia(7). 

C. pyxidata sharing space with C. coccifera on the flanks of Mount Evans. Note the tiny apothecia on C. pyxidata's splash cups, while those of C. coccifera are beefy and globular.

C. coccifera showing its more characteristic colors which earned it the moniker British Soldier lichen. As brilliant as its colors are, it is still easy to miss on forest floor. Each podetium in this photo is around 2-3 cm tall.

Cladonia coniocraea is a common cladonia of well-rotted (punky) pine logs on north-facing exposures. Its powdery appearance has earned it the name "common powderhorn," and it is legion on rotting logs throughout the state.

C. coniocraea again, forming a tiny forest of bone-like projections. Many are the Cladonia lichens which form slender, tentacle-like podetia: while I am reasonably sure of my ID, it could also be C. gracilis or C. cornuta.

Even more powderhorn lichen. I enjoyed the unearthly, forest-like effect this lichen creates.

C. cervicornis features multi-tiered stacks of fractalized cups, which may appear similar to antlers or to layered fountains.

 C. sulferina, or C. deformis: the two are separated primarily by chemical features. One source(8) argued that the two can be distinguished by the field character of how yellow-ish the thallus looks; presumably this works better if you have spent a lot of time looking at the two species side by side. 

C. cervicornis growing on rock, which is unusual. Presumably the organic matter from other lichens and mosses built up enough to provide a substrate for this erstwhile ground-dwelling species. The natural progression of lichen communities over time on stone is crustose, then foliose, then fruticose(2). In Colorado I have only found this to be true in very well-protected locations; by and large rock-dwelling (saxicolous) lichen communities in Colorado never make it past the foliose stage, presumably due to the harsh environment.  

C. pyxidata splash cups among mosses and (I think) club mosses on a hogback ridge in the foothills West of Denver. Note the propagules awaiting scattering by the next rain. A surprising amount of research has been devoted to exactly how far, on average, an isidium or similar structure may fly when struck by a raindrop; the gist of it is that lichens seem to propagate more densely over short distances by asexual means while the lighter apothecial spores move to establish new colonies over great distances of many miles(6). This strategy serves the lichens well: in some boreal environments the ground cover of Cladonia lichens can be so thick that it serves to modulate the soil temperature which in turn allows Pinus and other species to take root(2).

Thanks for checking out this information on the confusing but interesting genus Cladonia. I hope that next time you see some of these lichens on a forest floor, you take some time to admire them with newfound appreciation. 

References

1. Parnmen, S., Mongkolsuk, P., Rangsiruji, A., & Ahti, T. (2008). Phylogenetics of lichens in the genus Cladonia (Cladoniaceae) in northern and northeastern Thailand. Sauteria, 15, pp. 385-402.
2. Walewski, J. (2007). Lichens of the North Woods. Duluth, MN: Kollath+Stensaas Publishing
3. Weber, W. A., & Wittmann, R. C. (No Date). Consortium of North America Lichen Herberia: Research checklists: Colorado. Retrieved from http://lichenportal.org/portal/checklists/checklist.php?cl=1202&pid=510.
4. Osyczka, P., & Rola, K. (2013). Cladonia lichens as the most effective and essential pioneers in strongly contaminated slag dumps [electronic resource]. Central European Journal Of Biology, 8(9), 876-887.
5. Nash, T.H., Ryan, B.D., Gries, C., & Bungartz, F.(eds.)( 2001). Lichen Flora of the Greater Sonoran Desert Region. Vol 2., Tempe, AZ. Available at http://nhc.asu.edu/lherbarium/flora/index.php
6. Nash, H. T. III [Ed.](2008). Lichen Biology (full text). Cambridge: Cambridge University Press.
7. Corbridge, J. N., & Weber, W. A. (1998). A Colorado Lichen Primer. Niwot, CO: University Press of Colorado.
8. Nash, T.H., Ryan, B.D., Gries, C., & Bungartz, F.(eds.)( 2001). Lichen Flora of the Greater Sonoran Desert Region. Vol 2.  
9. Tempe, AZ. Available at http://nhc.asu.edu/lherbarium/flora/index.php