Painted Rocks: Yellow-Green

     In this post I would like to give some attention to two of the more salient yellow or yellow-green lichens that populate rocks in Colorado. As with the orange lichens that live here, the yellow lichens are fun to learn to identify because of their brilliant coloration that sets them apart from their rocky substrate, as well as their relative ease of identification even without magnification. The two species I have in mind are Pleopsidium flavum and Candelariella rosulans. As always with these lichen posts, feel free to bone up on your lichen terminology from this previous introductory post, as the language used when describing lichens can be quite unfamiliar. 

Pleopsidium flavum, honorable mention to Pleopsidium chlorophanum

     When I first took an interest in lichens, I noticed that many of the rocks around the foothills were not just red, gray, or brown as I might expect, but actually the chartreuse color of a glow stick or perhaps the radioactive goo from the Teenage Mutant Ninja Turtles cartoons. The organism responsible for this unexpected color shift is Pleopsidium flavum, a lichen that can grow to cover whole cliffs and which to my knowledge has no colloquial name. 

Pike's Peak granite providing a home to P. flavum and a Xanthoria species (orange). P. flavum's rosetted habit can be broken up by a bumpy substrate. I mostly included this photo as I felt it did credit to the intensity of this lichen's coloration.

     Confusingly, the only field guide-like treatment of Colorado lichens lists this species as P. chlorophanum(1). However a newer, more thorough review by Nash, Ryan, Gries, & Bungartz (2001)(2) maintains that while P. chlorophanum is assumed to occur at high altitudes in North America, it is quite rare (only one collection has been made in North America), and most Pleopsidium species that one encounters at lower altitudes are P. flavum(3). P. chlorophanum is a fascinating extremophilic lichen which thrives in Antarctica and has been shown to be able to actively photosynthesize and grow in simulated Martian conditions(4). The implications of this seem obvious:

Food for thought. The genus Pleopsidium could really use an Oscar win, anyhow.

However, until I get an angry missive from William A. Weber (author of A Colorado Lichen Primer) putting me straight, I am operating on the assumption that I have only ever seen the less researched but much more common P. flavum here in CO. P. flavum has a shiny, yellow-green thallus which prefers more acidic rock surfaces such as granite. Its areoles (distinct islands of thallus tissue) are around .5-1 mm in diameter, while the lobes around the thallus' margin are 1.5 to 2.3 mm across(2). Apothecia are the same color as the thallus, sunken, and >1 mm across. These measurements may be helpful for differentiating it from the highly similar aforementioned P. chlorophanum (if you manage to find it), but the only field mark you really need to identify this lichen is its intense coloration. No other lichen this color in our region is really shaped like P. flavum, so a mistaken identification is unlikely. Another oddity that is specific to P. flavum is its preference for growing on vertical surfaces, eschewing similar conditions on flatter rocks(1). The specific epithet flavum simply means "yellow," as apparently Latin lacks an adjective for "violently chartreuse."

P. flavum growing in a rosette on granite in the foothills near Boulder, CO. This photo provides a good reference for the relative sizes lobes, areoles, and apothecia. Apothecia are subtly visible towards the center of the thallus as circular darker patches ringed with lighter thallus tissue. 

The chartreuse coloration is due to the presence of rhizocarpic acid, which also lends its color to species such as Acarospora schleicheri and the ever-popular Rhizocarpon geographicum. Rhizocarpic acid is an interesting chemical in its own right, as it serves to absorb destructive UVA and UVB (ultraviolet) radiation, then re-radiate it on a spectrum usable for photosynthesis by P. flavum's photosymbiont, the alga Trebouxia(5). In this way, rhizocarpic acid serves to both shelter and nurture the photosymbiont needed for P. flavum to thrive and grow. This is a beautiful illustration of the symbiotic co-evolution of lichenized fungi and their photosynthetic partners, as rhizocarpic acid and other secondary metabolites in lichens are produced by the fungus, not the alga(6).

Large expanses of vertical stone can become overrun with P. flavum, which in this photo is sharing volcanic basalt with a Lecanora lichen, possibly Lecanora garovaglii. This photo was taken on the aptly-named Lichen Summit of North Table Mountain near Golden, which has a well-established population of P. flavum.

Candelariella rosulans and Friends 

Candelariella ssp. on granite in the foothills near Boulder, where C. rosulans was discovered. The "roses" of the apothecia are clearly visible but tiny even in this macro photo (click to enlarge). 

     There are a number of egg yolk-colored, crustose, tiny lichens that inhabit the rocks of Colorado at virtually every altitude. These are the Candelariellas, and they pepper communities of larger crustose lichens with their unmistakable color. C. rosulans is noteworthy because it was discovered in the foothills immediately outside of Boulder(1). It is the only Candelariella species that Corbridge and Weber bothered to highlight in their field guide, making it a sort of flagship for this genus in our area. The specific epithet means "little rose(7)" and likely refers to the apothecia, which have a crenulated, rose-like aesthetic when viewed under magnification. So too do all other rock-dwelling Candelariella species in our region, of which there are at least five(8), which also tend to have exactly the same coloration, preference for acidic rocks in sun, similarly sized squamules/areoles up to 1mm across, and similar chemistry (although not identical) as delineated by spot tests(2). The chemical that colors all Candelariellas the same bright yellow is calycin, which serves the same photoprotective and nurturing role as rhizocarpic acid does for P. flavum(5). Calycin-bearing lichens have also been used to dye wool yellow in Sweden(9), although I do not know if they have been used for this purpose in America. 

     Put simply, there is no good way to differentiate the species of this genus in the field that I am aware of, although microscopes and chemical testing can evidently parse them out. I find them rewarding to be able ID as a genus, however, as they are a distinctive, attractive, and relatively easy to parse down to the genus level. Nothing else in our region really looks like the Candelariellas. A truly intrepid amateur lichenologist who wishes to master this genus in spite of these challenges may find a list of Candelariella species in Colorado here. The lichens in the photos below may well all be C. rosulans simply because I took many of these pictures relatively close to the Boulder foothills. 

Candelariella ssp. growing on sandstone near Fort Collins, cohabitating with a handsome Caloplaca trachyphylla (orange at left). I have yet to find a crustose lichen community on stone that has not had some sort of Candelariella hiding between its larger lichen neighbors. Due to their tiny size, many Candelariellas are only apparent upon very close inspection, or even when examining macro photos after the fact. 

A tiny Candelariella lichen ekes out an existence between crystals of quartz at around 12,000 ft. elevation on Mount Evans. None of the quartz crystals in this photo are larger than .5 cm. 

     Thank you for taking the time to learn a little bit about yellow and yellow-green lichens! I find these a joy to behold when hiking as they contrast strongly with their surroundings and remind me that a complex ecological system is always humming along right next to me. 

References 

1. Corbridge, J. N., & Weber, W. A. (1998). A Colorado Lichen Primer. Niwot, CO: University Press of Colorado.
2. Nash, T.H., Ryan, B.D., Gries, C., & Bungartz, F.(eds.)( 2001). Lichen Flora of the Greater Sonoran Desert Region. Vol 2. Tempe, AZ. Retrieved from http://nhc.asu.edu/lherbarium/flora/index.php
3. Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2001. Lichen Flora of the Greater Sonoran Desert Region. Vol 3. Tempe, AZ. Retrieved from http://lichenportal.org/portal/taxa/index.php?taxauthid=1&taxon=53030&cl=1202
4. de Vera, J., Schulze-Makuch, D., Khan, A., Lorek, A., Koncz, A., Möhlmann, D., & Spohn, T. (2014). Adaptation of an Antarctic lichen to Martian niche conditions can occur within 34 days. Planetary & Space Science, 98182-190. doi:10.1016/j.pss.2013.07.014
5. Hidalgo, M. E., Fernández, E., Ponce, M., Rubio, C., & Quilhot, W. (2002). Photophysical, photochemical, and thermodynamic properties of shikimic acid derivatives: calycin and rhizocarpic acid (lichens). Journal Of Photochemistry And Photobiology. B, Biology, 66(3), 213-217.
6. Molnár, K., & Farkas, E. (2010). Current results on biological activities of lichen secondary metabolites: a review.
7. Numen, the Latin Lexicon (n.d.) Rosulans [entry in online dictionary]. Retrieved from http://latinlexicon.org/definition.php?p1=2051833
8. Consortium of North American Lichen Herbaria. (n.d.). Colorado [list in online database]. Retrieved from http://lichenportal.org/portal/checklists/checklist.php?cl=1202&pid=510  
9. Ethnolichenology of the World. (n.d.). Candelariella vitellina. Retrieved from http://web.uvic.ca/~stucraw/part2AM.html

Jewels of the Alpine Tundra

     During the winter months in Colorado, some of the higher reaches of the Rocky Mountains can reach temperatures as low as -40 degrees Fahrenheit(1), which puts the alpine tundra environment in a climate zone similar to much of Northern Canada or Scandinavia(2). On top of this, the soil of the tundra is riddled with rocks and gravel. Plants that grow in this zone have to be incredibly tough to survive and often have adaptations to survive in cold and wind such as short stature and coverings of hairs.
     These smaller plants also produce small, showy blossoms that cover the alpine tundra like precious gems, and which are a fantastic pleasure for sore hikers to behold. The way that tiny, exquisite alpine flowers seem to emerge from hiding might remind a reflective observer of the aesthetic principles used in Japanese gardening: as small features in the landscape give way to reveal them, each part of the garden should be a microcosm of the principles of natural beauty, only to be revealed from the proper perspective and within the proper context. A hiker who wants to appreciate these plants will need to slow down and stoop low, which fortunately is the involuntary modus operandi of an oxygen-starved, high-altitude hiker anyhow.
     I thought that the dead of winter would be a fun time to post about these impressive survivors, as they somehow manage to avoid tissue death in the arctic weather that we see in the high mountains from September through June. There are a large number of attractive and unusual species that populate the high alpine areas of the state. This post will take a quick and very non-exhaustive survey of the flowers that bejewel the high places of Colorado.
     For fear of writing redundantly, I will simply note here that all of the flowers featured in this post may bloom between July and August depending upon their elevation. Also, a handy chart of leaf shapes may be found here in order to clarify some of the terms used.

Eritrichium nanum, Alpine Forget-Me-Not     

E. nanum growing on the slopes of Pikes Peak. The brilliant yellow and and blue flowers 

are unlike anything else other than members of the same family. These plants 

were growing at around 12,000 ft elevation on a wet, north-facing alpine meadow.

The alpine forget-me-not in perspective. The tiny, fuzzy blue blob at the center 

of the photo (click to enlarge) is E. nanum, while the relatively large glossy leaves of 

Dryas octopetela at top right center are actually no longer than an inch. 

     The alpine forget-me-not is a great example of plants in the borage family, Boraginaceae. The five-petaled blue flowers, pubescence on stems and flower buds, and lanceolate leaves are all good field marks not just of this particular flower but of borage family flowers generally. A good rule of thumb in flower identification is that five-petaled flowers which are densely hairy are best investigated as Boriganaceae members before trying other families. This is seen in some other Colorado species such as the genera Cryptantha and Phacelia, although some related genera such as Mertensia give the hairs a skip. 

     The leaves are elliptic to obtuse and densely pubescent (covered in fine hairs), growing little more than a quarter inch long(3). This plant grows tightly appressed to the tundra soil, which coupled with its densely hairy foliage serve as adaptations against the punishing cold and wind of the alpine tundra. This flower is unmistakable for anything else that grows in its same climatic zone except for Myosotis alpestris, which is highly similar in appearance but larger and does not form small, silver mounds of foliage(4). 

Saxifraga chrysantha, Golden Saxifrage

S. chrysantha growing near 14,000ft on Mount Evans. Despite the showy flowers I 

almost missed these between the scree and granite boulders. 

     This flower presents a nice example of the sorts of saxifrages that we tend to see in Colorado, which frequently have low-growing, succulent leaves growing in rosettes and showy, colorful flowers with four or five petals. The perfectly formed rosettes of triangular to ovate leaves are so small that they might be mistaken by a fast-moving hiker for a moss. The fleshy yellow flowers, by comparison, are easy to see and to recognize. Each flower sports five petals and a yellow or  red conical to spherical center. The pedicels and the sepals will reveal a subtle pubescence when viewed with a hand lens(5). Blossoms and all, this plant will not grow higher than an inch or two. The  specific epithet chrysantha simply means "golden flower" in Greek. 

Androsace chamaejasme, Sweetflower Rockjasmine

A. chamaejasme growing around 11,500 ft on Pike's Peak. The flowers in this photo show 

the characteristic bright yellow center, which ages to an eye-popping pink. 

     Something about high altitude seems to love a tiny, pubescent flower with five petals and rosetted leaves. The trend continues with sweetflower rockjasmine, which has no relation to the fragrant tropical jasmines(6) nor, presumably, to the Disney princess. Despite this, its specific epithet means "low/ground jasmine." To add to the confusion, despite its superficial resemblance to flowers in Boraginaceae, this little flower actually hails from the primrose family: Primulaceae. Other members of this family such as those that I looked at in this post seem to bear little resemblance to this flower, so the phylogenic similarities must be fairly subtle.

     A. chamaejasme consists of succulent obtuse to elliptical leaves covered in a fine pubescence which grow in rosettes about 1/2 inch across. These give rise to pedicels not taller than two inches supporting an umbel of five-petaled flowers with bright yellow centers. Interestingly, as the blossoms age the centers of the flowers can turn a shocking bubblegum pink, even as other flowers on the same umbel retain their yellow coloration. I cannot find any information on why this is, but I assume it is due to the intense ultraviolet radiation present at high altitude wearing down the pigments in the petals. 

Dryas octopetala, Mountain Dryad

The flowers of D. octopetela form white mats in the high alpine tundra. The leaves are distinctively

shaped and tend to stand erect.

D. octopetela turning the flanks of Pike's Peak white. It often colonizes extensive areas. This 

Meadow was at around 12,000 ft elevation.

     Another beautiful, itty-bitty flower of the tundra is the aptly named Dryas octopetela, whose specific epithet simply refers to its eight petals. The lanceolate leaves are slightly glossy, have distinct crenate margins, and stand erect in (wait for it) rosettes, which in turn form great mats across the tundra. The white flowers are one to a stalk, and are superficially similar to globeflowers or marsh merigolds, but can be distinguished by their eight petals, the foliage of the plants, and the height of the flowers. D. octopetela hugs the ground while the other two species tend to grow taller. This is a circumpolar species which is well-distributed through alpine and arctic areas of the Northern Hemisphere(7). The relative ages of genetic lineages of D. octopetela in different regions are used in research on dating the advance and retreat of ice age glaciations.

Claytonia megarhiza, Alpine Springbeauty  

C. megarhiza in flower around 14,000 ft on Mt. Evans. "Springbeauty" is 

something of a misnomer, as this plant's spring (in terms of blooming) comes in 

late July to August.

The leaves of C. megarhiza turn a gorgeous shade of crimson when cold weather 

starts to set in. The autumn foliage is more noticeable and showy than the flowers.

This individual is stretching out and taking up space. I have noticed that when C. megarhiza 

grows at lower altitudes the leaves tend to be more variable and the plant larger. 

          This is probably my favorite wildflower in all the Rocky Mountains, although the flowers themselves are actually not terribly impressive. The sprawling, fleshy, glabrous, and obtuse to elliptic leaves can seem almost bawdy compared to the other tightly compact plants that inhabit the same life zone. C. megarhiza is also bigger than many plants which live in similar circumstances, with its rosettes reaching up to several inches in diameter. The five-petaled flowers may be pink or white and have a strong yellow coloration proximally. "Megarhiza" means "large root" and is an apt specific epithet as each plant is perched atop a colossal underground taproot. This root may reach up to a meter in length as it worms its way between cracks in the bedrock in search of water and anything resembling soil. An observant appreciator of plants in the purslane family, of which C. megarhiza is a member, will note a strong resemblance to the flowers of its lower altitude cousin Claytonia lanceolata. As noted in the photo above, C. megarhiza takes on a brilliant red hue as autumn sets in. A high slope may almost look like it's covered in rose blossoms as thousands of alpine springbeauties prepare themselves for dormancy. 

     Thank you for checking out this post on tiny alpine flowers. I find these flowers particularly pleasing and interesting to view and learn about due to their exaggerated geometry and the evanescence of their flowering season. I hope that this entry will help to spread my joy regarding these exceptional plants!

References 

1. United States Department of Agriculture [USDA]. (2012). USDA Climate Zone Hardiness Map. Retrieved from: http://planthardiness.ars.usda.gov/PHZMWeb/#
2. Peel et al (2007). Updated Köppen-Geiger climate map of the world. Retrieved from: http://people.eng.unimelb.edu.au/mpeel/koppen.html
3. Mammoser, D., & Tekiela, S. (2007). Wildflowers of Colorado. Cambridge, Minnesota: Adventure Publications, Inc.
4. Craighead, J. J., Craighead., F. C., & Davis, R. J. (1963). A Field Guide to Rocky Mountain Wildflowers. Boston, MA: Houghton Mifflin Company.
5. Schnieder, A. (n.d.) Saxifraga chrysantha. Retrieved from: http://www.swcoloradowildflowers.com/Yellow%20Enlarged%20Photo%20Pages/saxifraga%20chrysantha.htm
6. Androsace chamaejasme (n.d.). Retrieved 4 January, 2016 from https://en.wikipedia.org/wiki/Jasmine
7. United States Department of Agriculture [USDA](n.d.). Mountain avens. Retrieved from: http://www.fs.fed.us/wildflowers/plant-of-the-week/dryas_octopetala.shtml