how i found solorina crocea

solorina crocea is a charismatic peltigeroid lichen, with a flashy orange underside contrasting beautifully with its lovely green upperside. the genus' large, brown apothecia have given it the nickname "chocolate chip lichen".

during the winter of 2023, i found myself enamored with this lichen. due to its alpine ground and rock dwelling nature, it is not a lichen that could easily be found this time of year, so i made some plans for hikes where it seemed likely. browsing inaturalist, i noticed a very narrow elevation range where it seemed to pop up in washington. namely, it seemed to very much prefer being at a little under 6,000ft and up.

while identifying solorinas on inaturalist to get a feel for the species, i made a habit of zooming in on the location to view the elevation whenever i saw one, and sure enough it'd be at or around 6,000ft. using a local hike finding website, i searched for hikes with a high point above 6,000ft and settled on goat peak, a 6,400ft summit near mount rainier.

fast forward to summer of that year, i finally set out on the goat peak trail. while hiking, i kept an eye on my elevation, and i eagerly awaited crossing the 6,000ft point. mccune and geiser's indispensable macrolichens of the pacific northwest noted that it'd be found in "drainage seeps", indicating that i'd need a spot with some water. although i was certainly in the right place for it, i knew from experience that even with everything right, a lichen might simply not be there for whatever the reason.

right on cue, at 6,000ft a whole population of Solorina croceas lined the trail. having checked before setting out, i was astounded that no one had uploaded this population to inaturalist. they were everywhere! this was a spot with tree coverage, and i could see some liquid water flowing through here in the spring when everything's melting out.

after my lucky break, as i continued climbing, i wondered whether my 6,000ft rule was confirmation bias or not. certainly around this part of the cascades it's a useful rule, but it could easily be temperature based, or snowpack based, or something else. analyzing records from CNALH as well as inat, i found elevations of collections and observations to be (2304ft) 5400ft - 6510ft (8640ft).

an interesting exception was collected by Esslinger in 1980, on the north side of ruby mountain in washington. this record is only at 2,300ft: link. on inat, an observation with roughly the same elevation is here, near icicle creek. both of these localities are especially cold for their elevation.

it's hard to imagine why lichen would prefer such a narrow band like this. certainly lichen have varying degrees of cold hardiness, but given frequent ability to withstand desiccation, it seems like adapting to cold wouldn't be as big of an issue as it is. what's more strange to me is that Solorina seems to be absent below a certain elevation. maybe it's simply outcompeted by other Peltigeras, which grow faster in suitable habitats?

lichen which rely on cyanobacteria such as Solorina require liquid water to photosynthesize, so they tend to be less frequently found in dryer habitats, as well as exposed habitats. as i finished my hike up goat peak, the high elevation cascades forest broke out into an alpine area with krummholtzed trees. usual suspects for this habitat showed up: Letharia chief among them. in this exposed habitat i found no Solorina at all.

out of curiosity, i looked at a number of variables using the PRISM data source. here they are, all annual values:

(obvious but important caveat, i'm not entirely confident how clean all this data is, being sourced partially from inat and cnalh. inaccurate coordinates might be labeled as accurate in either data source, etc. (i removed some blatant ones from CNALH). naturally being from inat and various sources from CNALH, the data is subject to sampling biases)