Tuesday, January 29, 2008

A lichen Physcia tenella

I am an amateur trying to learn something about everything living in my garden

I promise to return to more sizable and familiar lifeforms soon, dear readers! For today's posting however: another lichen.

The lichen seen in photo 1 (click to enlarge) decorates many of the branches of my garden apple tree (at (1.2,1.5) - see here) and I'm almost certain (see shortly) in identifying it as Physcia tenella ('it' being either of the two greyish patches below the coin, as opposed to the yellow lichen left of the coin which - though I've not examined it is detail - is probably our old friend X. parietina)

The meaning of the Greek physcia (pronounced 'Fisk-ee-a') seems to be a matter of debate on the internet. I have come across it variously translated as "bellows", "breath-like", "sausage-shaped" and "blister"! Can anyone clarify the true meaning?

P.tenella is my blog's third example of a foliose lichen. According to my copy of the scholarly Lichens (F.S. Dobson, The Richmond Publishing Co.), Physcia lichens can be distinguished from other foliose lichens, in part, by their narrow (<~2mm) lobes, and septate spores (septa being thin, internal dividing walls - see here for some examples) - though I confess I've not looked for the latter.

Two further distinguishing features of P.tenella are i) the presence of eyelash-like cilia on the edges of the lobes. You can see these in the 40x-magnified photo 2. (Can anyone tell me what purpose it serves to lichen to 'sprout' these?) And ii) the presence of granular soredia (see here for my explanation of what these are) decorating the ends of the lobes. Were I to observe the soredia 'packaged' together inside little 'hoods' I understand I'd be looking at the closely similar lichen P.adscendens (since its not obvious they are, I'm sticking with my identification as P. tenella).

Finally, two nice facts about P.tenella I got from reading my copy of Lichens (O.Gilbert, The New Naturalist series). Firstly, P.tenella is one of three British lichen species favoured by long-tailed tits (Aegithalos caudatus) in building their nests (on average each nest contains nearly 3000 lichen flakes!). Secondly, being fairly acid- and nitrogen-tolerant (not all lichens are), in areas where people walk dogs, P.tenella is one of the commonest lichens to colonise the region marginal to that patch of tree-trunk known to professionals as "the canine zone" . It shouldn't be hard to imagine what this is!


skhoinarion said...

Hello, Henry!

First of all, I want to say that I've really enjoyed your recent blog entries (as always). They are not just informative, but also consistently well thought out and interesting.

I am writing here because I noticed your request on the meaning of Physcia. You are right in that the meanings usually offered for this word can seem to be a fairly incoherent jumble of unrelated items!

I'm not a professional etymologist, but I am quite interested in words and their origins, and happen to have a copy of Liddell and Scott's monumental doorstop of a book, their "Greek-English Lexicon" (9th edition, with Jones), sometimes abbreviated LSJ, so I can at least pass on what I find there; I hope it will shed some light on the matter. (LSJ can be, in my opinion, a little intimidating for those of us who aren't Greek scholars; the Intermediate and Abridged versions of the lexicon are much less so).

First of all, I think the genus name Physcia was probably derived from the following noun, which has a variety of meanings:

I. the large intestine, esp. as stuffed with pudding, sausage, black-pudding
II. blister or weal on the hand
III. gall-bag on a plant

As a root for this noun, LSJ gives a verb:

I. to blow or puff (as with bellows)
II. to puff or blow up, distend

[and several other things that are all along the same basic line]

Also related is another noun (my own comments are in square brackets)

I. a pair of bellows. 2. bladder. 3. "=pharetra" [a quiver for arrows] 4. "=askos" [a skin, but especially one made into a bag; hence our "ascus", "ascospore"!]
II. breath, wind, blast. 2. wind (in the body). 3. stream, jet (of fire). 4. [air-]bubble.
III. crater of a volcano

[and some more obscure ones, including some sort of fish. (Maybe a "puffer" fish?) :-) That's quite a varied list!]

So the basic idea is of things that are puffed up or inflated in appearance; various things that *can* be puffed up or inflated; or, by extension, things that are swollen or distended.

As an aside: The slime mould genus name "physarum" happens to be related to these words.

Incidentally, if you want to have a poke around the LSJ lexicon for yourself, you can do so at the Project Perseus site ("Dictionary Headword Lookup" tool). You would enter these words, for example, as phuske^, phusao^, phusa, in the search box. (Can be freely used by all; there's no registration process, fee, or anything like that).

Apologies for the length of this comment; please feel free to delete it if I have let my enthusiasm for words get ahead of me. Unless you already happen to know where to find this information, the search can be frustrating, so I felt I ought to pass on what information I could find.

Keep up the good work; all the best!


Henry Walloon said...

Hello skhoinarion

A huge thankyou - both for the kind words of encouragement and for solving the mystery of physcia's derivation.

Yet another thankyou for pointing me to the Project Perseus site. I hadn't known it existed, but I've done as you suggested and had a browse and I know I'll be returning to it many times in the future.



Anonymous said...

Yes this does indeed look like P.tenella. I have been examining some examples of lichens from Greenham Common, Berkshire and the hooded apperance of P.adscendens is quite distinct as you make clear. Also see http://www.stridvall.se/lichens/gallery/view_album.php?set_albumName=Physcia
As to the function of the cilia - what an interesting question. I've no idea but would love to find out.
Keep up the good work Henry.