Observation 105239: Physcia dimidiata (Arnold) Nyl.
When: 2012-08-03
(34.2522° -118.0951° 1450m)
Herbarium specimen reported

Notes: HABITAT shady oak-conifer forest on north slope; SUBSTRATE granitic rock by trail; ASPECT shaded; NOTES cortex K+y, medulla K-, very scant soredia under crenulate lobe tips, lower cortex prosoplectenchymatous.

Images

249460
20120803-99.jpg
249455
20120803-98.jpg
Physcia biziana below, Physcia dimidiata above.
249456
20120803-100.jpg
Physcia biziana below, Physcia dimidiata above, all damp.
249461
20120803-199.jpg
Lower surface of crenulate lobe tips, at 30x, stacked.
249462
20120803-200.jpg
Upper surface of crenulate lobe tips, at 30x, stacked.
249463
20120803-201.jpg
Upper surface of crenulate lobe tips, at 30x, stacked.
249464
20120803-202.jpg
Lower surface of crenulate lobe tips, at 30x, stacked.

Proposed Names

87% (1)
Eye3 Eyes3
Recognized by sight

Please login to propose your own names and vote on existing names.

Eye3 = Observer’s choice
Eyes3 = Current consensus

Comments

Add Comment
This was a real surprise to me
By: Jason Hollinger (jason)
2012-08-14 03:28:43 CDT (-0500)

I thought for sure this was P. tribacia, but I had just read somewhere by K. Knudsen that P. dimidiata and P. tribacia could be very difficult to distinguish. Really? All my specimens of P. dimidiata have obvious soralia, all my specimens of P. tribacia are like this, with sparse granular soredia scattered just under the crenulate lobe tips. Both have K- medulla. P. dimidiata has variable pruina (just like P. biziana — usually pruinose, but sometimes with little or none), P. tribacia has no pruina and is typically shiny.

There is, however, one either-or, black-and-white difference between the two: the cellular structure of the lower cortex. In P. dimidiata (like P. biziana, its fertile counterpart), the lower cortex is a woven mesh of long hyphae (prosoplectenchymatous); in P. tribacia, it is composed of a brickwork of round cells (paraplectenchymatous).

In fact, this specimen is prosoplectenchymatous. I immediately double-checked all my other (many) alleged specimens of P. tribacia, and was relieved to discover that they were, in fact, paraplectenchymatous, and therefor identified correctly. But here it is: a form of P. dimidiata which looks identical (except for the dull pruinose surface) to P. tribacia.

Just when you think you’ve got a species figured out…

Created: 2012-08-14 03:16:07 CDT (-0500)
Last modified: 2012-08-14 03:16:14 CDT (-0500)
Viewed: 76 times, last viewed: 2016-10-25 21:07:52 CDT (-0500)
Show Log