Observation 217013: Rhizocarpon disporum (Nägeli ex Hepp) Müll. Arg.

When: 2015-08-31

Collection location: Cactus Rock, Wisconsin, USA [Click for map]

Who: Andrew Khitsun (Andrew)

Specimen available

Proposed Names

29% (1)
Recognized by sight
92% (2)
Eye3 Eyes3
Based on microscopic features: 1 spore per ascus
57% (1)
Used references: ID provided by Jim Bennett

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Eye3 = Observer’s choice
Eyes3 = Current consensus


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I’d throw few bucks toward R.grande being present at the location too.
By: Andrew Khitsun (Andrew)
2016-02-08 22:21:00 CST (-0600)

There were so many of these at the location, and so variable that at the very least the three look-alikes must be there, and probably more as you mention.

There are others
By: Jason Hollinger (jason)
2016-02-08 22:13:03 CST (-0600)

But also not mentioned. Thomson claims R. eupetraeum and R. grande both have I+ blue medulla, R. disporum I-. Chemistry is probably also different. Maybe epihymenium color (I don’t normally trust that character any more for Rhizocarpon, though). Spore size and number of septae, might also be different… yeah Bennett’s measurements are too small for R. disporum. I’m afraid I don’t generally measure spores in this genus, though. :(

I think the best money is on both species being present.

Unfortunately, JB didn’t mention the number of spores per ascus.
By: Andrew Khitsun (Andrew)
2016-02-08 22:04:43 CST (-0600)

What about other micro characteristics: are they identical between the species, where the difference is only in the number of spores per ascus? The third morphologically identical species is R.grande, if I am not mistaken.

Yeah, these two species looks very similar macroscopically
By: Jason Hollinger (jason)
2016-02-08 21:45:07 CST (-0600)

R. disporum (1 spore per ascus) and R. eupetraeum (8 spores per ascus).

Jim Bennett identified this as Rhizocarpon eupetraeum
By: Andrew Khitsun (Andrew)
2016-02-08 21:28:55 CST (-0600)

Here is his micro:
spores 38×10-12 m., muriform, dark blue-green, 6 transverse, 1 long, some curved; medulla C-, K+y. Thomson found this species at the very same spot in 1986, out of very few localities in the state. Of course, there maybe two or three species present here in the photos – there is no way to distinguish them morphologically, I figure. The substrate is pre-Cambrian granite.

Created: 2015-09-26 20:48:09 CDT (-0500)
Last modified: 2016-02-08 22:21:59 CST (-0600)
Viewed: 70 times, last viewed: 2017-12-31 10:12:56 CST (-0600)
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