Lichen Walk at Arbrook Common - near Esher, Sunday 21st August

Led by Begoņa Aguirre-Hudson

The Society's yearly lichen walk took place along the left edge of the woods of Arbrook Common; after lunch, a few of us went on exploring the trees by the brook and right side of the Common boundary.  The main tree species examined for lichens were Oak, Birch and Alder, but an Elder (Sambucus nigra) on the left hand side of the car-park detained us for quite some time as it was covered with a large number of foliose species, mostly characteristic of the Xanthorion community, such as Phaeophyscia orbicularis, Physcia adscendens and Physconia grisea (all members of the Physciaceae family), Candelariella reflexa and Xanthoria parietina.  The latter two yellowish and orange species do not belong to the same systematic group - despite their colour - and can be separated easily in the field by using KOH on the thallus, reacting blood-red on the Xanthoria species and their relatives, and being negative on the Candellariella species.   Lecania cyrtella was our first crustose lichen there, but was not collected.


Abundant lichen specimens on an Oak


The fallen branches of the Elder were taken later to the lab at Kew to confirm the identity of a lichenicolous fungus growing as 'soot' on the fruit bodies and the thallus of the Xanthoria, and this, Xanthoriicola physciae, was a new record for Esher.  Also present on the same branch were two other new records for Esher, the lichenicolous Paranectria oropensis, very small pinkish-red dots found on Physcia tenella, and Punctelia ulophylla (Parmeliaceae).  The latter has only been detected in the British Isles this century and is thought to be spreading due to global warming.  It can be confused easily with Punctelia subrudecta, but a careful look at the tips of the lobes show that they are brownish and pruinose.  The marginal soralia are also more abundant than in P. subrudecta, although I found this character less reliable, since older specimens of P. subrudecta can also be rich in them.  All the specimens of these new records have been preserved dried in the herbarium of the Mycology Section at the Royal Botanic Gardens Kew.


Begoņa resorts to the 'Chemy' Lab


Within the woods, a compulsory stop was a leaning Oak, which was covered in mosses and foliose species of the Parmeliaceae - remember their shiny upper surfaces - and Cladoniaceae - characterised by the two types of thallus, squamules at the base and upright podetia in the shape of goblets (Cladonia fimbriata) or pointed (Cladonia coniocraea).  Among the Parmeliaceae we saw Flavoparmelia caperata (yellowish, medulla KOH-), Melanelia glabratula, M. subaurifera, Parmotrema perlatum and Punctelia subrudecta. Parmelia sulcata, one of the commonest species of the family in Esher, was also encountered on fallen branches.   Higher up on the trunk of this tree was Phlyctis argena, a whitish crustose lichen with a distinctive KOH+ blood reaction, another new record for Esher! Material of this species was more abundant on the Poplars and collected that afternoon.  Of course the most widespread species on the Oaks in shady situations is Lepraria incana, and this was abundant in Arbrook; on Birch, with a dark green thallus, the equivalent is Dimerella diluta (look for the diaphanous fruit bodies to be certain).  Also on Birch we found Arthonia spadicea, Opegrapha atra, and Cladonia coniocraea.  The former two species have Trentepohlia as photobiont instead of the more common chlorococcoid algae.


The leaning Oak identifications continue


Finally, another new record for the commons was Arthopyrenia analepta, found and collected at the end of the morning walk as just small dots on Sorbus aucuparia.  The species of this genus and those of Leptorhaphis (see below) are usually under-recorded due to their small size, and are only facultatively lichenised.

Other species not mentioned above, but also observed on the day were:

Candelariella vitelina (on fence, by car park)

Chaenotheca ferruginea (on Oak trunk)

Cliostomum grifithii (on Oak trunk, near Arbrook Farm)

Hypotrachyna revoluta (on Oak trunk)

Leptorhaphis atomaria (on Aspen, specimen kept in Kew)

Porina chlorotica (on the roots of a Beech tree on Longy Down, specimen kept in Kew)

Although in general terms the lichen cover is probably less rich than at West End Common (a morning walk there two years ago yielded 25 species of which three were new records), all-in-all it was quite an exciting day!

BEGOŅA AGUIRRE-HUDSON

 

A bonus item:

From Chris Brading's garden: Robin's (as in 'Goodfellow') Pincushion, 'Sprite-of-the-Woods' or the Bedegour Gall - Diplolepsis rosea (Hymenoptera) on Rosa Canina