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Journ. Hattori Bot. Lab. No. 53: 345-349 (July 1982)
LICHENS OF THE ARID MEDITERRANEAN
AREA AND NORTH AFRICA
X. LLIMONA
1
INTRODUCTION
The area surveyed in this report has a diverse climate. It ranges from the ex-
treme, continental desert environments of the central Sahara to the semi-arid areas
of south-east Spain, characterised by hot summers and mild winters (Fig. 1).
FLORA
Reviewing the lichen flora of these regions is problematic since the taxonomy is
rather confused. Most of the early authors described material collected by others.
Thus, they could not recognize the variability of the species. The collected material
is widely spread over many European herbaria and the descriptions published in many
different minor journals. There is only little synthetic work e.g. the unfinished study
of Harmand (1905-1913) or recently Ozenda and Clauzade (1970).
As in other arid areas, the flora is not very rich, but presence and density of
species may be high in habitats favoured by frequent dew, shade and protection from
the wind. In hyperarid and arid "oceanic" deserts, with dew or fog (coastal desert
between Agadir and Villa Cisneros, Fuerteventura and Lanzarote, Cabo de Gata,
Negev, etc.) a conspicuous biomass of lichens is developed. Most of the saharosindian
lichens are reported from mountainous regions (Ahaggar, Tibesti). Travellers de-
scribe the central Saharan plains as devoid of lichens. Wind erosion, rarity of dew
and perhaps "desert varnish" may be the main causes for this.
Endemism has been probably overemphasized by misinterpretation of environ-
mental modifications, overestimations of minor details, or redescription of species by
neglecting "concealed" bibliography.
VEGETATION
There have been phytosociological studies on silicicolous and gypsicolous lichen
vegetation in Spain, and on calcicolous, terricolous and epiphytic lichen vegetation in
Spain and the south of France.
Two main types of arid regions may be distinguished in SE Spain:
1.
With
warm winters,
characterized by thermophilous species sensitive to low minimal
winter temperatures, such as:
Xanthoria resendei, Dimelaena radiata, Lecanora montagnei,
Teloschistes villosus, Ramalina canariensis, Arthothelium crozalsianum,
and
Caloplaca
subochracea.
2.
With cold winters, in continental semi-steppic areas such as the central Ebro Valley and
1
Department of Botany, Faculty of Sciences, University of Murcia, Spain.
346
Journ. Hattori Bot. Lab. No. 53
1 9 8 2
FIG. 1. Arid regions of the Mediterranean area and North Africa. Clima types
according to Walter and Lieth (1967) are indicated: 111, subtropical dry belt; IV, typical
mediterranean climate with winter rainfall; VII, semiarid continental climate.
the area south of Madrid, with xerophilous but cold tolerant species as
Diploschistes
steppicus, D. ocellatus, Psora saviczii, Acarospora placodiiformis, A. reagens, Fulgensia
desertorum, Buellia zoharyi, B. epipolia
and the vagants
Teloschistes lacunosus
and
Spha-
erothallia
spp.
A
silicicolous vegetation is known from SE Spain, coastal W Africa and the
Canary Islands. In these areas insolation is a main selective ecological factor. Shaded
surfaces show associations characterized by:
Lecanora montagnei, L. schistina, Per-
tusaria gallica, Buellia cerussata, B. subdisciformis, Ramalina requienii
(Al. Lecanorion
montagnei Llimona, belonging to S. O. Pertusarienalia leucosorae Egea et Llim.).
Where air humidity is higher, extensive patches of
Pertusaria monogona
are
present,
and in fog oases, populations of
Ramalina tingitana
and
R. clementeana
can be found.
Communities on insolated surfaces share species like
Xanthoria aureola, Caloplaca
subpallida, Parmelia glomellifera, Lecanora muralis
(S. 0. Parmelienalia conspersae
Llimona et Egea). Characteristic of such surfaces is Al. Dimelaenion radiatae
Llimona. This is an extremely xero-, thermo- and heliophilous alliance, with
Dimelaena
radiata, Ramalina bourgeana, Xanthoria resendei, Caloplaca gloriae, C. scoriophila,
Acarospora charidema, A. maroccana
and
Lecanora sulphurella.
A
less thermophilous,
but rather nitrophilous alliance (Al. Caloplacion irrubescentis Llimona et Egea)
contains
Caloplaca irrubescens, Acarospora heufleuriana, Buellia tergestina, Parmelia
tinctina, Solenopsora holophaea
and
Diploicia subcanescens.
X. LLIMONA
:
Lichens of the Arid Mediterranean Area
347
Rain-tracks show special lichen populations rich in cyanophiles, such as
Peltula
euploca, Gonohymenia cribellifera
and
Lichinella stipatula.
A characteristic species
on flints in dew deserts of North Africa is
Ramalina maciformis,
well known in the
Negev (with
Caloplaca ehrenbergii)
and also found on the Canary Islands.
The calcicolous lichen vegetation is not as rich as that of siliceous rocks. A well
known ombrophilous association is the Caloplacetum subochraceae (Roux, 1978), from
Provence, coastal mediterranean Spain, Portugal and North Africa. The Dirinetum
repandae (Clauz. et Roux, 1975) is preferentially ombrophobous and covers with an
almost continuous white crust the calcareous shaded cliffs at the coast, and, in a
lesser development, up to 30 km inland. It is characterised by
Dirina repanda, D.
stenhammarii
and
Opegrapha grumulosa.
Under high air humidity it is also char-
acterised by
Roccella fucoides.
Sunny rocks show disjunct populations of tolerant species such as
Caloplaca
aurantia, Buellia epipolia, Xanthoria aureola, X. isidioidea, Diploschistes ocellatus
and
Caloplaca lactea.
The populations extend out of the region on to the coast of southern
Marocco (Alta et al., 1972). Species of
Thyrea
and
Anema
or related genera appear
in raintracks in arid habitats such as the mountains of the Sahara (Faurel et al., 1953).
The terricolous vegetation in the arid regions consists of a scattered higher plant
cover with large areas of soil between them which are colonized by lichens. Lichens
prefer soils with a crust, e.g. some calcareous soils, loess or gypsaceous soils (Llimona,
1974; Crespo & Barreno, 1975), found mainly in the Ebro Valley and south of Madrid.
The typical soil crust community, Acarosporetum placodiiformi-reagentis Llimona,
1974, is a mixture of
Diploschistes steppicus, Acarospora placodiiformis, A. reagens,
Psora saviczii, Fulgensia desertorum
and
Buellia zoharyi.
Sites with very high humidity
are enriched by fruticose or more or less vagant lichens:
Teloschistes lacunosus,
Cladonia subrangiformis
and
Cladonia endiviaefolia.
More or less closely related photophobous communities grow on hard gypsum,
(Al. Lecideion gypsicolae Crespo et Barr., 1975): they resemble communities in the
Irano-Turanian region. On arid soils rich in carbonate we find lichen communities
related to the Toninion coeruleonigricantis consisting of
Fulgensia fulgida, Toninia
coeruleonigricans, Psora decipiens
and a terricolous form of
Diploschistes ocellatus.
In
S. E. Spain and N. Africa, and the Saharo-Arabian region the Heppiaceae and
Derma-
tocarpon
are common (Galun in Friedmann, 1970).
On cryoarid and cryoturbated soils there are communities of the Al. Sphaero-
thallio-Parmelion vagantis (Crespo et Barr., 1978) dominated by vagant lichens.
Sphaerothallia-species
are characteristic of communities in steppic highlands of Spain,
eastern N. Africa as well as oriental steppic regions, (the Lower Volga plain, Iran,
Turkey, Greece).
Because of lack of space we do not treat epiphytic vegetation, which has more
properly a "subdesertic" character.
ECOLOGY
Accumulation of nutrients on surfaces is favoured by scarcity of rain washing,
348
Journ. Hattori Bot. Lab. No. 53
1 9 8 2
thus eutrophic conditions arise preponderantly on flat surfaces. This explains the
general presence of nitrophilous species on such surfaces. Porous, stable rocks
(e.g. lava) and rough bark increase significantly the nutrient retention.
First measurements of the micro-climate and field measurements of the water
uptake of
Teloschistes lacunosus
and other species in the central Ebro Valley (Llimona,
1974) gave similar results to those from the Negev.
Typical desert adaptations are frequent in our area. A thick cortex is typical
for soil lichens as
Psora decipiens
(90 ,um); and for lichens on sunny rocks,
Acarospora
charidema
(120-269
,um), Caloplaca gloriae
(65 pm).
Psora decipiens
and
Squamarina
species have epinecral layers of about 20
pm.
A pruina is perhaps the most efficient
protection against radiation. The pruina of
Psora sariczii
measures 20-43 ,um and
in
Acarospora placodirformis
40 ,um. Many species are intensively pigmented: they
are brown, red, yellow or black. In some exposed lichens of arid regions the algae
are aggregated in dome-shaped clumbs or are arranged in chains perpendicular to
the surface
(Acarospora charidema, Xanthoria resendei)
(Llimona, 1975).
Ramalina
bourgeana, Gonohymenia
and
Lichinella stipulata
and soil forms of
Collema cristatum
prevent damage from sun radiation by exposing only apical parts of the thallus to the
air.
TABLE I. Life form spectra of lichen vegetation in arid areas around the Mediter-
ranean Sea.
Crustose
Foliose
Fruticose
Inner Sahara
97
3
0
Negev
91
6
3
Sierra del Cabo de Gata (Spain)
sunny lava surfaces
84
11
5
shaded lava surfaces
70
11
19
Volcanic islands near Cabo de Palos
(SE Spain)
84
7
9
Ebro Valley on gypsum soil
Acarosporetum placodiiformi-reagentis
(dry)
95
5
0
ditto, but with high dew fall
71
17
12
Teloschistes lacunosus,
with its villose surface area, is a good example of an ad-
aptation to improved air moisture absorption (Llimona, 1974). Soil lichens have
long rhizinic strands as e.g.
Squamarina crassa
and
Acarospora reagens
growing on
gypsum or loess.
As in all deserts and subdeserts the life form spectrum is dominated by crustose
species (Table 1).
Finally it is remarkable that many species contain norstictic acid, including the
prominent gypsicolous species (e.g.
Acarospora reagens, Psora decipiens, Buellia
almeriensis)
and the species (e.g.
Lecanora schistina, Acarospora heufleuriana, Buellia
subdisciformis, Aspicilia intermutans
and
Pertusaria monogona)
on lava in the Sierra
del Cabo de Gata.
X. LLIMONA
:
Lichens of the Arid Mediterranean Area
349
REFERENCES
Asta,
J.,
G. Clauzade et P. Ozenda (1972). Lichens du SW marocain. Rev. Bryol. Lichenol. 38:(2)
299-303.
Crespo, A. et E. Barreno (1975). Ensayo floristic° y ecologic° de la vegetaciOn liquenica de los
yesos del centro de Espana.
(Ftdgensietalia desertori).
An. Inst. Bot. A.J. Cavanilles 32(2):
873-908.
Crespo, A. et E. Barreno (1978). Sobre las comunidades terricolas de liquenes vagantes
(Sphareo-
thallio-Xanthoparmelion vagantis
al. nova). Acta Bot. Malacitana
4:
55-62.
Faurel, P. Ozenda et G. Schotter (1953). Les lichens du Sahara Algerien. Bull. Res. Counc. Israel.
Desert Research, Spec. Publ.
2:
1-8.
Galun, M. (1974). Desert algae, lichens and fungi.
In
E. L. Friedmann (ed.), Desert Biology, Vol.
II:
165-212. Adademic Press Inc., New York.
Harmand, J. (1905-1913). Lichens de France. 1185 pp. Klinksieck, Paris
Llimona, X. (1974). Las comunidades de liquenes de los yesos de Espana. Univ. de Barcelona.
Secr. de Public. 18 pp.
Llimona, X. (1975).
Xanthoria resendei
Poelt et Tay. en el SE de Espana, fitosociologia y corologia.
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1-24.
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801 pp.
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