Observation 86108: Acarospora socialis H. Magn.

When: 2011-12-27

Collection location: Organ Pipe Cactus National Monument, Pima Co., Arizona, USA [Click for map]

32.0° 112.0°

Who: Chris Parrish (kitparrish)

No specimen available

Locality: Diablo Wash, Ajo Mountains, Organ Pipe Cactus National Monument, Pima Co., Arizona, USA; 32° 0’36.63"N, 112°43’53.46"W, el. 695 m

Substrate and habitat: Growing on rough talus boulders in cactus and thorn scrub desert on the lower slopes of the Ajo Mountains.

Identification: Non-effigurate yellow Acarospora in Pima County, Arizona, might be asssigned to either Acarospora contigua or Acarospora socialis (leaving aside the related genus Pleopsidium for the moment). Consider the following comments from the treatments of these two species on CNALH:

Acarospora contigua

“Acarospora contigua is easily identified by its epruinose, rimose-areolate thallus, but it can be confused with other species, like A. socialis, which have an areolate stage in their development, or with the effigurate species when the edge is missing. … Few specimens were seen during this study and this species needs a more extensive investigation.”

Acarospora socialis

“upper surface: bleached white or green-yellow to various shades of yellow, usually glossy, convex to flat, smooth to rough, usually fissured, often rugulose, pruinose or not

“Substrate and ecology: on sandstone, volcanic or granitic rocks or outcrops on ridges, slopes or vertical walls, all exposures, rarely on consolidated soil or growing on other crusts

“Sonoran distribution: common throughout Arizona, southern California, Baja California, Baja California Sur, and Sonora.

“Notes: Acarospora socialis is the most common yellow Acarospora in southwestern North America. The synonyms of A. socialis attest to its extreme polymorphism.

“In its early development, A. socialis can be confused with A. contigua, but a careful study of thalli will usually reveal some areoles becoming lobed and squamulose in the case of A. socialis.”

The CNALH range map for Acarospora contigua includes only 5 localities in Arizona and one each in neighboring California, Baja California, Sonora, and New Mexico, while Acarospora socialis is reported as “the most common yellow Acarospora in southwestern North America.” Yellow Acarospora is abundant in the Ajo Mountains, sometimes seemingly painting the walls of high canyon cliffs, so in light of the remarks on CNALH, a conservative treatment might simply assign them all to Acarospora socialis and leave to the experts more sophisticated analyses of putative specimens of Acarospora contigua.

Sharnoff’s Acarospora contigua gallery
Sharnoff’s Acarospora socialis gallery

Acarospora of Pima County, Arizona

The CNALH checklist of the lichens of Pima County, Arizona lists 13 species of Acarospora. They can be sorted as follows into the five categories of Acarospora organized by Kerry Knudsen in his analysis of the genus for the “Lichen Flora of the Greater Sonoran Desert Region, Vol. 3” (2007, pp. 1-38):

Sections 1 and 2 : thallus yellow, pruinose or not; on rock

Section 1 : thallus with gyrophoric acid (C+ and KC+ red, K-) or norstictic acid (C-, KC-, K+ yellow turning red)


Section 2 : thallus lacking both gyrophoric and norstictic acids (C-, KC-, K-)

Acarospora contigua
Acarospora socialis

Section 3 : thallus yellow or brown or white; on soil

Acarospora schleicheri
Acarospora socialis

Section 4 : thallus brown or whitish brown; on rock; cortex or medulla C+ red

Acarospora interspersa
Acarospora obpallens
Acarospora fuscata

Section 5 : thallus brown or whitish brown or white; on rock; cortex and medulla C-

Acarospora badiofusca
Acarospora veronensis
Acarospora strigata
Acarospora obnubila

Not included in the Lichen Flora of the Greater Sonoran Desert Region:

Acarospora americana (Knudsen, K., J.C. Lendemer and R.C. Harris. 2011)
Acarospora cinereoalba (Knudsen, K., J.C. Lendemer and R.C. Harris. 2011) – listed as a synonym of Acarospora americana in the most recent Wetmore checklist (May 2011)
Acarospora smaragdula (= Silobia smaragdula)

Proposed Names

28% (1)
Recognized by sight
56% (1)
Eye3 Eyes3
Used references: Knudsen in Nash et al., Lichen Flora of the Greater Sonoran Desert, Vol. 3" (2007, pp. 1-38)

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Eye3 = Observer’s choice
Eyes3 = Current consensus


Add Comment
Looks too squamulose
By: Jason Hollinger (jason)
2012-01-11 09:04:25 UTC (+0000)

… for the typical A. socialis. Don’t suppose you got to do a C test on it. ;) Seriously, though, there are only a few truly squamulose yellow Acarospora. You might have a chance.

Created: 2012-01-11 04:48:50 UTC (+0000)
Last modified: 2012-01-12 17:17:34 UTC (+0000)
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