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You’re right, Chris, fascinating set of photos from 2007 and 2009!
You can really see new apothecia being produced all around the central ~half of the thallus, and the existing ones have all grown quite perceptibly.
Like Chris said, you can also see a distinct chlorotic zone around the margin in 2007 in a number of places, but there’s no sign of this in 2009, where it has recovered and looks quite healthy and vigorous. Perhaps a die-back in 2007 due to drought or other unfavorable conditions?
It is interesting to note the intermediate status of Dirinaria between true foliose and true crustose in that it is rapidly overgrowing all the crustose species around it (e.g. the Haemotomma in the upper left), but is being itself overgrown by two parmelioid lichens (top and bottom right). Yet it is also overgrowing what look like a Pyxine (top, true foliose species with rhizines and everything) and another Dirinaria (D. picta?, left).
For those interested in minutia:
For area, I drew over the outline of the lichen in Gimp, filled it in, and created a black-and-white mask, black where the lichen was, white elsewhere. I counted the number of pixels black in both images. (I have a program that needed only slight modifications to produce this number for me from a tiff file.)
Then I calibrated the relative size of the two images by comparing the distances in pixels between two mature apothecia on either side of the thallus (again, using Gimp to measure distances). This assumes that the thallus is only growing at the edge, which I believe is safe in this case, and indeed most cases. (Lichens have “pseudomeristem” tissue along the margins, much like plants.)
pixels in thallus in 2009: 2566546
pixels in thallus in 2007: 1411871
conversion factor: 0.813034188034188
(That is multiply distances in the 2009 image by 0.81 to be equivalent to the distances in 2007 image.)
Result is 20.16% growth.
I also measured the distance from a central apothecium to 12 points along the edge of the thallus at 30° intervals. The growth in each direction, clockwise from “due north” (straight up):
(1) Note that the thallus is being overgrown in the “southeast” by some parmelioid lichen, it is obscured in the “east” by the Ramalina, and the “southern” edge is off the photo in 2009. I estimated each of these by just drawing a straight line between the closest point on the edge that were visible.
Life seems to be somewhat better now for this fellow than it was in 2007, but actually it’s remarkable how little it has changed over that period. The radius seems to be only somewhat larger, and it’s easy to find corresponding patches of apothecia. The inner apothecia have grown in diameter, and new ones are popping up out on the periphery. Since the peripheral area is larger than the inner area, does this mean we get more new apothecia per year in an older thallus (??) Did you make any measurements to document this growth? … increase in diameter? … gains (and maybe losses due to herbivory or damage) in apothecia? Do you have any photos of smaller individuals? Matching photos for a range of thallus sizes could document growth over its life cycle. Well done, vcharny!
Created: 2009-05-27 22:08:21 CDT (-0400)
Last modified: 2009-05-27 22:08:21 CDT (-0400)
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