Excerpts from Jim Conrad's
from the January 27, 2013 Newsletter issued from the valley of the Dry Frio River in northern Uvalde County, southwestern Texas, on the southern border of the Edwards Plateau, USA
PERFORATED RUFFLE LICHEN
Bark of large, spreading, lower branches of our abundant Texas Live Oaks is likely to bear a crust of lichens -- mainly the Eastern Speckled Shield Lichens and Cartilage Lichens we've already looked at, but also less frequently occurring species. One of those less conspicuous yet not uncommon species is the foliose, grayish white lichen on a low live oak branch shown above.
In that picture there's a second lichen, a darker, warty one, at the lower left in the picture, but we're not talking about that one.
Using the excellent but rather technical "Dynamic Key" at the LichenPortal.Org website at http://lichenportal.org, the main lichen in our picture was identified as the Perforated Ruffle Lichen, PARMOTREMA PERFORATUM, described as usually found on trees in open habitats but sometimes on rocks. It occurs here and there worldwide.
On other lichens we've seen that the craterlike growths visible on several of the lichen flakes, or thalli (singular thallus), are apothecia. Apothecia are reproductive structures produced by the fungal component of the lichen, and of course lichens are "composite organisms" composed of a fungus and an alga and/or a cyanobacterium. The apothecium's inner surface is covered with innumerable, microscopic, tubelike affairs called asci (singular ascus) stacked next to one another and containing spores (ascospores), which escape from the tubes' tops. When the fungal spores land in a good spot they germinate, their mycelium wrap around an appropriate alga or cyanobacterium cell, and begin growing into a lichen.
Many lichen species produce apothecia. However, the Perforated Ruffle Lichen's thalli bear something else less commonly observed on foliose lichens, and that's the slender, black, hairlike structures along the ruffled margins of the thalli. Those black hairs are called cilia and in lichen identification they are important because most lichens don't have them, but some do. Moreover, from species to species, the cilia's general appearance and disposition along the thalli margins vary greatly.
Most lichens reproduce more vegetatively via fragmentation than they do sexually, so I had always assumed that cilia on lichens bearing them would disintegrate and each tiny cilia particle would then form a new lichen. However, to form a new lichen asexually you need to have both fungal and algal cells bundled together, but lichen cilia are purely fungal in nature, consisting of bundles of fungal hyphae. I can't find an explanation of the purpose of lichen cilia, despite the fact that the ruffle lichen genus Parmotrema seems to regard them as desirable.