Lichens

by Annie Lorrain Smith

A very careful tabulation of lichens at Blakeney Point in Norfolk was made by McLean[1197] and the table on p. 386 is reproduced from his paper. Sand, he writes, is present in all the associations and the presence or absence of stones marks the great difference between the two formations determined by dune and shingle.

(1) Bare sand, which is the first association listed, is an area practically without phanerogams; the few lichen plants, Cladonia furcata and Cetraria aculeata f. acanthella, are attached by slight embedding in the soil.

(2) Grey dune. The sand-loving lichens of the association grow in company with Hypnum cupressiforme and attain their greatest development. Other species which also occur there are Parmelia physodes and Evernia prunastri var. stictocera.

(3) Derelict dune. This part of the dune formation occurs here and there on the seaward margin where the grey dune has been worn down by the wind. It is more shingly, hence the presence of stone lichens; dune phanerogams are interspersed and with them a few fruticose lichens, such as Cladonia furcata.

(4) High shingle. The term indicates shingle aggregated into banks lying well above all except the highest tides. A large percentage of sand may be mixed with the stones and if no humus is present and the stones of small size, lichens may be absent altogether. Those occurring in the “loose shingle” are saxicolous. In the “bound shingle” where there is no grass the stones, fixed in a mixture of sand and humus, are well covered with lichens. With the presence of grass, a thin layer of humus covers the stones and a dense lichen vegetation is developed both of shingle and of dune species.

(5) Low shingle. This last association lies in the hollows among plants of Suacda fruticosa. Stability is high and tidal immersions regular and frequent. The dominant factor of the association is the quantity of humus and mud deposited around and over the stones. The lichens cover almost every available spot on the firmly embedded pebbles. The characteristic species of such areas are Lecanora badia and L. (Placodium) citrina which effect the primary colonization. To these succeed Lecanora atra and Xanthoria parietina. In time the mud overwhelms and partly destroys the lichens, so that the phase of luxuriant growth is only temporary.

Lecanora badia is conspicuously abundant at the sand end of this formation. Lecanora (Placodium) citrina disappears as the mud is left behind. Collema spp. also occur frequently on the mixture of mud and sand round the stones. The species on “low shingle” are those most tolerant of submersion: Verrucaria maura is confined to this area, where it is covered by the tide several hours each day.

Formation	Association			Principal Species
Dune	1. Bare Sand			Cetraria aculeata f. acanthella
				Cladonia furcata
	2. Grey Dune			Cladonia rangiferina, Peltigera rufescens
				Cladonia furcata, Cl. alcicornis
	3. Derelict Dune			Cladonia furcata, Parmelia fuliginosa
				Rhizocarpon confervoides
Shingle	4. High Shingle	Loose	With sand	Lecanora atra, L. galactina
				Rhizocarpon confervoides
				Lecanora citrina
			Without sand	Physcia tenella, Lecanora citrina, Xanthoria parietina
				Squamaria saxicola
				Parmelia saxatilis, P. fuliginosa
		Bound	With grasses	Cladonia rangiferina, Cl. furcata, Cl. pungens
				Cetraria aculeata
			Without grasses	Xanthoria parietina, Biatorina chalybeia, Lecanora atra
				Aspicilia gibbosa, Buellia colludens, Verrucaria microspora
				Physcia tenella, Lecanora atroflava
	5. Low Shingle			Rhizocarpon confervoides, Lecanora citrina var. incrustans
				L. badia, L. atra, Xanthoria parietina
				Verrucaria maura

McLean adds that Xanthoria parietina in its virescent form on Suaeda fruticosa also endures constant immersion; Lecanora badia does not occur above the tidal line and Lecanora galactina does not descend below tidal limits; the latter is an arenicolous species and colonizes some of the loosest and sandiest areas of shingle. Rhizocarpon confervoides is ubiquitous.