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	THE LICHENS OF BONSAI TREES Whilst reading the article by Michael Kirby in White Admiral 68 and studying the associated picture, it occurred to me (CH) that the dark areas on the tree trunk amongst the moss could be a foliose lichen (Peltigera sp.), so I contacted Michael and went over to have a look. In the field, the darkness on the east side of the stump turned out to be damp decaying bark. On the north side there was a lichen present, growing amongst moss, Cladonia chlorophaea with a number of podetia (pixie cups) which initiate fruiting in this genus, and on the west side, shaded by a shrub, a small quantity of Lepraria incana. At the same time that I was recording these species, Michael invited me to look at the lichens that were growing on bonsai trees, which he had grown from seed. This paper deals with their identification. There were four bonsai trees present: a hornbeam, a red-leaved maple, a field maple and a horse chestnut, and each had a different lichen assemblage. Hornbeam (Carpinus betulus) mostly had Melanelixia subaurifera on the main branches, with Xanthoria parietina on twigs. Physcia adscendens, P. tenella, two thalli of Lecanora chlarotera, and Xanthoria polycarpa were also present and on the base, Lepraria incana and Amandinea puntata were seen. An immature Cladonia sp. was found on moss surrounding the tree in the dish, but was too small to be sure what it was. a) Xanthoria parietina - foliose with marginal lobes and apothecia (fruiting bodies) b) Melanelixia subaurifera - foliose with marginal lobes and finger-like projections (isidia), which abrade to powdery patches c) Physcia tenella - foliose with cilia (white arrow) and powdery reflexed lobe ends d) Physcia adscendens - similar to the above with hooded internally powdery lobe ends Red-leaved ornamental maple (Acer palmatum) the main lichen in the centre of the tree was Xanthoria parietina, with an odd thallus of Lecidella elaeochrom and Arthonia radiata spreading on twigs. Lecanora chlarotera and Amandinea punctata were also noteNovember 19, 2011 9:03hlarotera.jpg" width="500" height="373" />	e) Lecanora chlarotera - crustose with pale margined apothecia on a whitish thallus. (white arrow)
	f) Lecidella elaeochroma - crustose with black bun-shaped apothecia on a greenish white thallus

Field maple (Acer campestre) also had Xanthoria parietina in the centre of the tree, with a small quantity of Physcia tenella and Lecanora expallenson the base. Horse chestnut (Aesculus hippocastanum) had virtually no lichens present at all. The trees which were approximately 20-30 years old were grown in shallow pans and were about 30 cm high except for the horse chestnut which was 65 cm high. This tree was sown in 1975 and in spite of its dwarf nature has produced an inflorescence for the last three years. The trees had the stunted appearance associated with bonsai treatment, but the trunks had not yet achieved the gnarled state one expects in this kind of tree and the lichens reflected this. Arthonia radiata and Xanthoria polycarpa are typical twig species and were on the smallest branches. Many of the other lichens present are able to exist in a wider amplitude of bark roughness from smooth to roughish, and had taken up residence in an appropriate niche, and the Lepraria incana was sheltering in dry shade at the base of one of the trees. The Cladonia sp. had favoured the well-drained moss surrounding the base of the trees in the pans, a habitat, suggestive of heathland, where they are usual and often abundant.

	g) Arthonia radiata - crustose with stellate black apothecia sunk in the thin thallus
	h) Cladonia chlorophaea - fruticose fruiting body (“pixie cup”) with granules and folioles (white arrow) and fruit initials on the rim

With trees, the substrate topography, governed by age (bark roughness), is not the only criterion that governs where a lichen will grow since other parameters come into play such as hardness, porosity and hence water retention, pH and light. It is also very likely that the genome of the tree itself plays a significant role. There is another important factor which affects lichen colonisation in any situation. This is atmospheric pollution, such as sulphur or nitrogen compounds. Gaseous sulphur dioxide from fossil fuels (coal and oil) is not particularly harmful, as it blows away but when, in contact with water, it is turned into sulphuric acid (acid rain) and will to a greater or lesser extent destroy the lichen association by killing the algal partner. Mineralised nitrogen from car exhausts and farming practices (manure and fertilizers) can have the opposite effect. Some lichens require more nitrogen than others for growth and do very well in this nitrogen-rich environment. Xanthoria parietina, once abundant only on coastal rocks, due to bird droppings, and on some trees inland is considerably increasing and dominating some roadside trees nowadays to the exclusion of other species which may retreat or die out. Physcia adscendens and P. tenella, also in the Xanthorion parietinae alliance are similarly increasing for the same reason.

These variables will undoubtedly account for the differences in the lichen species noted on the four trees looked at. Mature hornbeam boles are not usually good due to the hard smooth nature of the bark and their occurrence in the drier parts of Great Britain. Not much is known about colonisation of branches in the canopy where light intensities will be high and the effects of higher concentrations of nitrogen compounds more noticeable.

In the present study, the hornbeam had the richest assemblage of species. The two maples would be expected to have a good cover, as in natural conditions they do, and this was to some extent true. This is because being basic the bark will nullify the effects of acid rain and allow the lichens to grow. The horse chestnut was also behaving as expected. It is usually a very poor tree lichenologically, due to a heavy dark canopy and acidic bark. The acid rain exacerbates the problem like a double whammy effect because in the low rainfall area in which the tree was growing surface leaching of the bark cannot occur, which would raise the bark pH and allow some lichens to come in.