Collection location: Sintra, Portugal [Click for map]
Of the four species of Phaeographis existing in the Iberian Peninsula – P. dendritica, P. lyellii, P. inusta and P. smithii- only the first and the last have spores of similar dimensions, the other two having smaller spores. The values given in Ref. 1 are:
P. dendritica: (26-)30-40(-45) x 6-9 um;
P. smithii: 25-40(-45) x 7-9.5 um.
I obtained the following average values: Me = 41.1 × 7.7 um ; Qe = 5.4 (N=30), with values for the lenght in the range 27 – 55 um and about 15% of the spores have lenght above 50 um.
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sum(score * weight) /
(total weight + 1)
from the people who observed Graphidaceae in Georgia makes part of the scenario where those lichens and, in general, lirellate lichens make part of a world apart. It happens that these are ones of my favorite lichens and I intend to know more about them, if I can. Let see what I will find in the future, but judging from what I found recently we have many things here which I was not aware before.
I was talking with some fellows doing an extremely extensive and exhaustive survey of all the lichens in every county of Georgia — and there are many counties in Georgia! They’ve been at it for over 10 years. It’s safe to say they have more experience with Graphidaceae (and many other groups of lichens!) than you and I will ever have, put together. Their comment on this subject was simply: “We completely ignore spore sizes and number of septae listed in the literature; they’re always wrong.” No doubt this was an exaggeration, but perhaps there’s a kernel of truth: if your spores are close — especially the average — maybe we should be happy and lower our expectations!
You probably already know all of this, but it’s worth throwing out there: Ideally you only want to measure mature spores which were expelled naturally from the ascus. In some genera this can actually be done: wet the hymenium very thoroughly until it’s soft and squishy, then cut gently so as not to damage any asci. Any spores floating free will be pretty close to mature.
This technique worked remarkably well for me on a batch of problematic Lecanora last summer. I was getting all sorts of aberrant spore measurements before, but after applying this technique dilligently, I suddenly magically started to get consistent (and correct!) measurements.
But with Graphidaceae this is a completely different story. As we commented on earlier: they don’t seem to naturally release their spores at all in many cases! So which are mature, and how do you tell?? Maybe we should expect our spore measurements to be all over the place. And how conscientious do you think the folks describing these species were? I’m just saying…
you posted about the species under consideration, but I´m affraid that my problem are not the dscriptions but the interpretation that I make of them. For instance:
- Let assume that, as it may happen in N.A. according to those data, here the spores of P. dendritica can reach 50 um. As I said in the notes, 15% of the spores are bigger than that. Is a bit too much. OK, my scope can be not very well calibrated, though 10% of error is a bit too much (spores with (real) 50 um that I measured as having 55 um). But four times?
- If I´m interpretng correctly the photo of the section, the base of the exciple is closed, black and not very thickned.
- This will lead to P. dendritica. The rest of the details, including the number of septa of the spores are in accordance with the description.
Now, this is not the first specimen for which the dimensions of the spores doesn’t fit into the ranges given in the description (see _ooservation 163951). So, what is wrong?
Here’s what Bruce Ryan said:
17a. True exciple entire, continuous (closed) below hymenium; spores (6-)8-10(-11)-celled. Ascospores (18-)26-42(-50) x (6-)8-11(-13) µm. Norstictic acid. Ascocarps somewhat emergent, never sessile, to 0.4 mm wide; exciple black, not greatly thickened below; thalloid margin never prominent or stromatoid. New England to Florida, west to Texas and Nebraska. . . . P. dendritica (Ach.) Müll. Arg.
17b. True exciple open and colorless towards the base; spores 6-8-celled. Thallus smoother, often continuous or only sparingly rimose-cracked. Ascocarps often shorter, less branched, rarely radiating-dendroid; thalloid exciple indistinct to weakly distinct. Hymenium 80-100 µm tall. Ascospores 26-40 × 7-9.5 µm. Thallus P+ orange, K+ red (crystals), KC+ red, C-, UV-
(norstictic acid). On bark, Washington state. . . . P. smithii (Leighton) de Lesd.
(Be easy on Ryan, his keys were never meant to be published!!)