Selvagens

Nova Hedwigia, Beiheft 138, 187–199 Stuttgart, November 2010

Article

The Selvagens Islands bryoflora and its relation with islands of the Madeira and Canary Islands Archipelagos Manuela Sim-Sim1, 2, Susana Fontinha3, Leena Luís1, 2, Carlos Lobo4 and Michael Stech5 1

2

3

4

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Universidade de Lisboa, Faculdade de Ciências de Lisboa, DBV, Centro de Biologia Ambiental, C2, Campo Grande, 1749-016 Lisboa, Portugal (corresponding author: msimsim@fc.ul.pt) Museu Nacional de História Natural, Jardim Botânico/CBA, Rua da Escola Politécnica, n° 58, 1250-102 Lisboa, Portugal Centro de Estudos da Macaronésia (CEM), Universidade da Madeira, Campus da Penteada, 9000-390 Funchal, Madeira, Portugal Jardim Botânico da Madeira-Eng° Rui Vieira/CEM, Quinta do Bom Sucesso, 9064-512 Funchal, Madeira, Portugal; Netherlands Centre for Biodiversity Naturalis, section Nationaal Herbarium Nederland, Leiden University, P. O. Box 9514, 2300 RA Leiden, The Netherlands

With 4 figures and 2 tables

Abstract: The bryoflora of the Selvagens Archipelago is characterised and updated based on results from recent fieldwork, and compared with those of Madeira and Canary Islands. The bryoflora of Selvagens Islands includes 16 taxa, four of which are reported for the first time for these islands. As a result of its small area and strong saline influence, low habitat diversity is present on Selvagens Archipelago determining most of its bryophyte diversity, which is dominated by acrocarpous mosses and mainly by species adapted to stressful conditions. Due to its topography, the Selvagens bryoflora is quite distinct from the other islands of Madeira Archipelago. Cluster analysis revealed closest relationships with the driest islands of Madeira Archipelago (Desertas Islands and Porto Santo), and with the Canary Islands of Fuerteventura and Lanzarote. Recent revisions in the course of this comparison also revealed new taxa for the bryoflora of Desertas and Porto Santo, namely one and eight species, respectively.

Key words: Bryoflora, Canary Islands, dry areas, Madeira Archipelago, Selvagens Islands

Introduction The uninhabited Selvagens Archipelago is situated in the North Atlantic at approximately 300 km south of Madeira Island and 180 km north of the Canary Archipelago (Fig. 1). It consists of a group of small islands of volcanic origin, Selvagem Grande, Selvagem Pequena and Ilhéu de Fora, which originated from the same volcanic hotspot as the Canary Islands and have an estimated age of 27 Myr (e.g., Geldmacher et al. 2005). This archipelago constitutes the southernmost part of the Portuguese territory and is administrated by the Madeira Autonomous Region. © 2010 J. Cramer in Gebr. Borntraeger Verlagsbuchhandlung, Stuttgart, Germany

www.borntraeger-cramer.de

1438-9134/2010/0138-0187 $ 3.25

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Fig. 1. Location of the Selvagens Archipelago.

Selvagens Islands are protected since 1971 as a strict Nature Reserve; therefore the use of the terrestrial and marine areas is very restricted. In 1997 the European Diploma for Protected Areas Category A was awarded to Selvagens Islands, hereby placing them under the auspices of the Council of Europe. More recently they were included as a site of the Natura 2000 Network (SPNM 2004).

The knowledge concerning the bryoflora of the Selvagens Archipelago is scarce. Only a small number of researchers have published some data records for these islands during the last 68 years.

The first seems to be by Luisier (1942), who refers the collection of Heterocladium heteropterum (Brid.) Schimp. by Custódio Fernandes in Selvagem Pequena, representing the only reference to this small island. Afterwards Nóbrega (1955) refers seven mosses and only one liverwort to Selvagem Grande, then Eggers (1982) indicates seven taxa for that island. More recently Sérgio et al. (2008) published a list of the bryophytes of Madeira, referring nine taxa (eight mosses and one liverwort) to the Selvagens Archipelago. During the last years several plant sociological relevés have been made by Kürschner et al. (2008a, b) on the Madeira Archipelago (Madeira , Porto Santo and Deserta Grande) resulting in an increase in the number of bryophyte taxa in relation to the latest bryophyte list (Sérgio et al. 2008).

The main aim of this work is to present an updated list of the bryoflora of Selvagens Archipelago. In addition, a characterization of its bryoflora, concerning the main taxonomical groups (mosses and liverworts) and phytogeographic affinities (including endemics) is presented. We also analyse the bryoflora of Selvagens comparatively to the other Islands of Madeira Archipelago concerning their bryophyte richness and composition, with a brief overview of its relationships with the bryoflora of Canary Islands, the geographically and geomorphogically closest archipelago.

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Material and methods Study area. The Selvagens Archipelago is situated between 30° 01′ 35″ and 30° 09′ 10″ N, 15° 52′ 15″ and 16° 03′ 15″ W in the Atlantic Ocean (Fig. 1). It is composed of three small islands and several islets, in total about 2.73 km2. Geologically the islands are of volcanic origin and have never been part of the African continent (Carvalho & Brandão 1991).

The highest altitude is Pico da Atalaia (163 m a.s.l.) on the Selvagem Grande. This island has an area of approximately 245 ha, is roughly pentagonal in shape and crowned by a plateau that is about 100 m a.s.l. In general, the landscape is rugged and the coastline made of sheer drops resulting from sea erosion (SPNM 2004). The other two small islands are located at about 20.37 km southwest of Selvagem Grande: Selvagem Pequena, with an area of 20 ha and the highest peak at 49 m a.s.l., and Ilhéu de Fora, with an area of 8.1 ha and the highest peak at 18 m a.s.l.

The islands represent remains of volcanic peaks and their area almost doubles at low tide (SPNM 2004).

Selvagem Grande is made up from porous scoria, which due to erosive processes gave rise to a brittle terrain and a soil with a vitrified surface and a nicrolitic structure. Its visible base is composed of foralite and nephelinite, upon which a thick layer of yellowish calcareous sand was deposited (Carvalho & Brandão 1991). On this island, there is an extensive subterranean gallery, where a bed of lime sulphate of saccharoid crystallization was deposited. There are also various shell beds dating back to different geological epochs, from the Miocene up to more recent times (Carvalho & Brandão 1991).

A subtropical maritime climate is prevailing. Although the islands are under the influence of the dominant northeasterly trade winds, their low altitude does not favour cloud condensation.

Nevertheless, it seems that in the past, these islands must have been influenced by higher humidity conditions, which can be inferred from the presence of a great profusion of sub-fossil shells of land snails. Occasional westerly winds carry dust from the Sahara desert as well as high temperatures to the islands (SPNM 2004).

The present plant cover is mainly composed by herbaceous, saxicolous halophytes, some endemics [e.g., Misopates salvagense D. A. Sutton, Argyranthemum thalassophilum (Svent) Humphries], within ecosystems in an unaltered state (Selvagem Pequena and Ilhéu de Fora), which have remained untouched by human activities. The vascular flora is comprised by approximately 105 taxa of which 7 are endemic to this group of islands. In fact, Selvagens Archipelago presents the highest density of endemic species per km2 in the entire Macaronesian region. Of these species, we point out, Monanthes lowei (Paiva) Pérez et Acebes (an endemic species to Selvagens and endemic genus to Macaronesia) and Euphorbia anachoreta Svent., existing only on Ihéu de Fora (Press & Short 1994).

Fieldwork and herbarium studies. In order to study the bryoflora of Selvagens Archipelago, fieldwork was carried out in Selvagens Islands, namely on Selvagem Grande (at least once a year between February 2002 and August 2008). Bryophyte material was collected all over Selvagem Grande Island, in rock crevices and fissures as well as on soil depressions on the top where humidity is high enough for the development of small bryophyte populations. Although the bryophytes are not abundant on the island, a higher frequency of bryophytes was observed on soil depressions, where some water accumulates during short periods, especially in winter time. The specimens revised are deposited in LISU, MADJ and MADS herbaria. Aditionally, the specimens from Porto Santo and Desertas are also deposited in LISU, MADJ and MADS herbaria.

Data analysis. In order to clarify the relation of Selvagens bryoflora to the other islands of Madeira Archipelago as well as of Canary Islands, data concerning the species referred for each island were gathered. The Madeiran Archipelago bryoflora is compiled in Sérgio et al. (2006,

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2008). Subsequent additions were made by Luís et al. (2007, 2008, 2010), Stech et al. (2007), Blockeel (2008), Kürschner et al. (2008a, b), Lobo (2008), Fontinha et al. (2010), Sim-Sim et al. (2008, 2010). Relating to Canary Islands, we considered the list of bryophytes published by González-Mancebo et al. (2008), excluding the doubtful taxa. Nomenclature follows Ros et al.

(2007) for liverworts and Hill et al. (2006) for mosses, except for Isothecium prolixum (Mitt.)

Stech, Sim-Sim, Tangney & D. Quandt, which follows Stech et al. (2008), and for families Frey & Stech (2009).

Collection data were subjected to a cluster analysis based on presence and absence data for each taxon in each island of Madeira, Selvagens, and Canary Islands Archipelagos. Euclidean distance was used as a distance measure and weighted pair group average as the linkage method.

Cluster analysis was performed in Statistica 9.0 (StatSoft 2009).

Results and discussion New data on the bryoflora of Selvagens Archipelago The bryoflora from Selvagens Archipelago comprises 16 species. Four species are new to Selvagens bryoflora, namely Bryum dichotomum, Riccia atlantica, Riccia lamellosa and Tortula solmsii, indicated by an asterisk in the list below.

MARCHANTIOPHYTA Ricciaceae *Riccia atlantica Sérgio & Perold Selvagens Archipelago: Selvagem Grande, Pico dos Tornozelos, N and NE sided, 30° 08′ 54.485″ N, 15° 51′ 57.079″ W, 136 m, on rock cracks and under the rocks on coastal exposed areas, April 2005, Silva (MADJ), (LISU), s.n.

*Riccia lamellosa Raddi Selvagens Archipelago: Selvagem Grande, Topo, 30° 08′ 54.581″ N, 15° 52′ 09.772″ W, 100 m, exposed, dry and rocky area, Febr. 2005, Silva (MADJ),(LISU) s.n; Selvagem Grande, plateau between Pico dos Tornozelos and Pico Atalaia, 30° 08′ 54.581″ N, 15° 52′ 09.772″ W, 100 m, exposed, dry and rocky area, Aug. 2008, Fontinha & Sim-Sim (MADJ), (LISU), s.n.; Selvagem Grande, plateau between Pico dos Tornozelos and Pico Atalaia, 30° 08′ 54.581″ N, 15° 52′ 09.772″ W, 100 m, exposed, dry and rocky areas, Aug. 2008, Fontinha & Sim-Sim (MADJ), (LISU) s.n.

Riccia sorocarpa Bisch.

Selvagens Archipelago: Selvagem Grande (Nóbrega 1955); Selvagem Grande, Pico Atalaia (N), 30° 08′ 49.567″ N, 15° 52′ 25.022″ W, 153 m, exposed, dry, windy and rocky area, Apr. 2006, Fontinha (MADJ), (LISU), s.n.; Selvagem Grande, Topo, 30° 08′ 54.581″ N, 15° 52′ 09.772″ W, 100 m, exposed, dry and rocky area, Febr. 2005, Silva (MADJ), (LISU) s.n; Selvagem Grande, plateau between Pico dos Tornozelos and Pico Atalaia, 30° 08′ 54.581″ N, 15° 52′ 09.772″ W, 100 m, exposed, dry and rocky area, Aug. 2008, Fontinha & Sim-Sim (MADJ), (LISU), s.n.

BRYOPHYTA Bryaceae Bryum caespiticium Hedw.

Selvagens Archipelago: Selvagem Grande (Nóbrega 1955, Eggers 1982).

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Bryum canariense Brid.

Selvagens Archipelago: Selvagem Grande (Nóbrega 1955).

*Bryum dichotomum Hedw.

Selvagens Archipelago: Selvagem Grande, Pico Atalaia (N), 30° 08′ 49.567″ N, 15° 52′ 25.022″ W, 153 m, exposed, dry, windy and rocky area, Apr. 2006, Fontinha (MADJ), (LISU), s.n.; Selvagem Grande, Topo, 30° 08′ 54.581″ N, 15° 52′ 09.772″ W, 100 m, exposed, dry and rocky area, Febr. 2005, Silva (MADJ), (LISU) s.n.; Selvagem Grande, Pico dos Tornozelos (N, NE), 30° 08′ 54.485″ N, 15° 51′ 57.079″ W, 136 m, rock cracks and under the rocks, Apr. 2005, Silva (MADJ), (LISU), s.n.; Selvagem Grande, Pico dos Tornozelos (N), 30° 08′ 54.485″ N, 15° 51′ 57.079″ W, 136 m, Aug. 2008, Fontinha & Sim-Sim (MADJ), (LISU), s.n.; Selvagem Grande, plateau between Pico dos Tornozelos and Pico Atalaia, 30° 08′ 54.581″ N, 15° 52′ 09.772″ W, 100 m, exposed, dry and rocky area, Aug. 2008, Fontinha & Sim-Sim (MADJ), (LISU), s.n.; Selvagem Grande, Topo, 30° 08′ 54.581″ N, 15° 52′ 09.772″ W, 100 m, exposed, dry and rocky coastal area, Aug. 2008, Fontinha & Sim-Sim (MADJ), (LISU), s.n.; Selvagem Grande, Topo, 30° 08′ 54.581″ N, 15° 52′ 09.772″ W, 100 m, exposed, dry and rocky area, Aug. 2008, Fontinha & Sim-Sim (MADJ), (LISU) s.n.

Fissidentaceae Fissidens sublimbatus Grout Selvagens Archipelago: Selvagem Grande, Pico dos Tornozelos, N and NE sided, 30° 08′ 54.485″ N, 15° 51′ 57.079″ W, 136 m, on rock cracks and under the rocks on coastal exposed areas, 30 Apr. 2005, Silva (MADJ), (LISU), s.n.; Selvagem Grande, plateau between Pico dos Tornozelos and Pico Atalaia, 30° 08′ 54.581″ N, 15° 52′ 09.772″ W, 100 m, exposed, dry and rocky areas, Aug. 2008, Fontinha & SimSim (MADJ), (LISU) s.n. (Fontinha et al. 2010).

Fissidens viridulus (Sw. ex anon.) Wahlenb. var. incurvus (Starke ex Röhl.) Waldh.

Selvagens Archipelago: Selvagem Grande (Nóbrega 1955, Eggers 1982).

Pottiaceae Pottia lanceolata (Hedw.) Müll.Hal. Selvagens Archipelago: Selvagem Grande (Nóbrega 1955, Eggers 1982).

Pottiopsis caespitosa (Brid.) Blockeel & A. J. E. Sm. Selvagens Archipelago: Selvagem Grande, Topo, 30° 08′ 54.581″ N, 15° 52′ 09.772″ W, 100 m , exposed, dry and rocky area, Febr. 2005, Silva (MADJ), (LISU), s.n. (Sim-Sim et al. 2010).

Tortella flavovirens (Bruch) Broth.

Selvagens Archipelago: Selvagem Grande (Nóbrega 1955, Eggers 1982); Selvagem Grande, Pico dos Tornozelos (N, NE), 30° 08′ 54.485″ N, 15° 51′ 57.079″ W, 136 m, rock cracks and under the rocks, Apr. 2005, Silva (MADJ), (LISU), s.n.; Selvagem Grande, plateau between Pico dos Tornozelos and Pico Atalaia, 30° 08′ 54.581″ N, 15° 52′ 09.772″ W, 100 m, exposed, dry and rocky areas, Aug. 2008, Fontinha & SimSim (MADJ), (LISU) s.n.

Tortula atrovirens (Sm.) Lindb.

Selvagens Archipelago: Selvagem Grande (Nóbrega 1955, Eggers 1982).

Tortula muralis Hedw.

Selvagem Grande (Nóbrega 1955, Eggers 1982).

Tortula pallida (Lindb.) R. H. Zander Selvagens Archipelago: Selvagem Grande, Pico Atalaia (N), 30° 08′ 49.567″ N, 15° 52′ 25.022″ W, 153 m, exposed, dry, windy and rocky area, Apr. 2006, Fontinha (MADJ), (LISU), s.n.; Selvagem Grande, Topo, 30° 08′ 54.581″ N, 15° 52′ 09.772″ W, 100 m, exposed, dry and rocky area, Febr. 2005, Silva (MADJ), (LISU) s.n.; Selvagem Grande, Pico dos Tornozelos (N, NE), 30° 08′ 54.485″ N, 15° 51′ 57.079″ W, 136 m,

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rock cracks and under the rocks, Apr. 2005, I. Silva (MADJ), (LISU), s.n.; Selvagem Grande, Pico dos Tornozelos (N), 30° 08′ 54.485″ N, 15° 51′ 57.079″ W, 136 m, Aug. 2008, Fontinha & Sim-Sim (MADJ), (LISU), s.n.; Selvagem Grande, plateau between Pico dos Tornozelos and Pico Atalaia, 30° 08′ 54.581″ N, 15° 52′ 09.772″ W, 100 m, exposed, dry and rocky area, Aug. 2008, Fontinha & Sim-Sim (MADJ), (LISU), s.n.; Selvagem Grande, Topo, 30° 08′ 54.581″ N, 15° 52′ 09.772″ W, 100 m, exposed, dry and rocky coastal area, Aug. 2008, Fontinha & Sim-Sim (MADJ), (LISU), s.n.; Selvagem Grande, Topo, 30° 08′ 54.581″ N, 15° 52′ 09.772″ W, 100 m, exposed, dry and rocky area, Aug. 2008, Fontinha & Sim-Sim (MADJ), (LISU) s.n. (Luís et al. 2010).

*Tortula solmsii (Schimp.) Limpr.

Selvagens Archipelago: Selvagem Grande, Pico dos Tornozelos, N and NE sided, 30° 08′ 54.485″ N, 15° 51′ 57.079″ W, 136 m, on rock cracks and under the rocks on coastal exposed areas, Apr. 2005, Silva (MADJ), (LISU), s.n.

Heterocladiaceae Heterocladium heteropterum Bruch & Schimp.

Selvagens Archipelago: Selvagem Pequena (Luisier 1942, Eggers 1982).

The citation by Luiser (1942) about the presence of Heterocladium heteropterum on Selvagem Pequena should be considered doubtful since the name of the collect locality could be a mistake.

Due to the characteristics of this species and the lack of any fountain in this island its occurrence at Selvagem Pequena is very unlikely, and the species has never been collected or identified by one of the authors (S. Fontinha) who visited Selvagens at least once a year since 2002.

New data on the bryoflora of Desertas and Porto Santo Islands As a result of recent revisions, new taxa are referred to the bryoflora of Desertas and Porto Santo islands, namely one and eight taxa, respectively.

MARCHANTIOPHYTA Aytoniaceae Asterella africana (Mont.) A. Evans Porto Santo: Pico Ana Ferreira, 33° 02′ 57″ N, 16° 22′ 04″ W, 94–150 m, crevices and rock base, March 2007, Fontinha & Sim-Sim (MADJ), (LISU) s.n.; Pico Castelo, 33° 04′ 50″ N, 16° 20′ 01″ W, 360–437 m, crevices and rock base, March 2007, Fontinha & Sim-Sim (MADJ), (LISU) s.n.

Ricciaceae Riccia atlantica Sérgio & Perold Porto Santo: Pico Ana Ferreira, 33° 02′ 57″ N, 16° 22′ 04″ W, 94–150 m, crevices and rock base, March 2007, Fontinha & Sim-Sim (MADJ), (LISU) s.n.

Targioniaceae Targionia lorbeeriana Müll.Frib.

Porto Santo: Pico Ana Ferreira, 33° 02′ 57″ N, 16° 22′ 04″ W, 94–150 m, crevices and rock base, March 2007, Fontinha & Sim-Sim (MADJ), (LISU) s.n.

Lophocoleaceae Lophocolea bidentata (L.) Dumort.

Porto Santo, Pico Ana Ferreira, 33° 02′ 57″ N, 16° 22′ 04″ W, 94–150 m, on crevices and rock base, March 2007, Fontinha & Sim-Sim (MADJ), (LISU) s.n.; Rocha de Nossa Senhora, 33° 04′ 50″ N, 16° 20′ 01″ W, 360–437 m, crevices and rock base, March 2007, Fontinha & Sim-Sim (MADJ), (LISU) s.n. This taxon was found on two new localities though it was already referred to the island (Lobo 2008).

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BRYOPHYTA Bryaceae Bryum radiculosum Brid.

Deserta Grande: top of Vale da Castanheira, 32° 3′ 39,24″ N, 16° 31′ 33,11″ W, 400–444 m, on soil between grasses, March 2007, Fontinha & Sim-Sim, (MADJ), (LISU) s.n.

Leucobryaceae Campylopus brevipilus Bruch & Schimp.

Porto Santo: Pico Ana Ferreira, 33° 02′ 57″ N, 16° 22′ 04″ W, 94–150 m, crevices and rock base, March 2007, Fontinha & Sim-Sim (MADJ), (LISU) s.n.

Ditrichaceae Ceratodon purpureus (Hedw.) Brid.

Porto Santo: Pico Castelo, 33° 04′ 50″ N, 16° 20′ 01″ W, 360–437 m, crevices and rock base, March 2007, Fontinha & Sim-Sim (MADJ), (LISU) s.n.

Funariaceae Entosthodon obtusus (Hedw.) Lindb.

Porto Santo: Rocha de Nossa Senhora, 33° 04′ 50″ N, 16° 20′ 01″ W, 360–437 m, crevices and rock base, March 2007, Fontinha & Sim-Sim (MADJ), (LISU) s.n.

Gigaspermaceae Oedipodiella australis (Wager & Dixon) Dixon Porto Santo: Pico Castelo, 33° 04′ 50″ N, 16° 20′ 01″ W, 360–437 m, crevices and rock base, March 2007, Fontinha & Sim-Sim (MADJ), (LISU) s.n.

Pottiaceae Leptophascum leptophyllum (Müll.Hal.) J. Guerra & M. J. Cano Porto Santo: Pico Castelo, 33° 04′ 50″ N, 16° 20′ 01″ W, 360–437 m, crevices and rock base, March 2007, Fontinha & Sim-Sim (MADJ), (LISU) s.n.

Comparison of the bryoflora of Selvagens and Madeira Archipelagos The Selvagens bryoflora is represented mainly by mosses (81 %) and to a lesser extent by liverworts (19 %). No hornworts were found (Table 1, Fig. 2). Compared with the islands of Madeira Archipelago, the mosses are higher represented and the liverworts show the lower representativity (Fig. 2). For example, in Porto Santo the liverworts are highly represented (53 %) and Table 1. Number of bryophyte taxa present in Madeira and Selvagens Archipelagos.

Hornworts Liverworts Mosses Total

Madeira Island

Porto Santo

Desertas

Selvagens

6 176 359 541

4 70 59 133

4 30 63 97

– 3 13 16

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Fig. 2. Proportion of mosses (䊏), liverworts (䊐) and hornworts (䊏) in Selvagens Archipelago and the other islands of Madeira Archipelago.

Table 2. Madeiran endemic bryophyte taxa on each island of Madeira and Selvagens Archipelagos. × present.

Madeira Region Taxa

Madeira Island

Porto Santo

Desertas Islands

Selvagens Islands

× ×

– –

– –

– –

× × × × – × × × × ×

– – – – × – – × – –

– – – – × – – × – –

– – – – – – – × – –

Brachythecium percurrens Hedenäs Brachythecium rutabulum (Hedw.) Schimp. var. atlanticum Hedenäs Bryoxiphium madeirense A. Löve & D. Löve Echinodium setigerum (Mitt.) Jur. Fissidens microstictus Dixon & Luisier Fissidens nobreganus Luisier & P.de la Varde Frullania sergiae Sim-Sim et al.

Nobregaea latinervis Hedenäs Porella inaequalis (Gottsche ex Steph.) Perss.

Riccia atlantica Sérgio & Perold Thamnobryum fernandesii Sérgio Tylimanthus madeirensis Grolle & Perss.

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Fig. 3. Proportion of acrocarpous mosses (䊐) and pleurocarpous mosses ( ), thallose liverworts (䊏), foliose liverworts (䊏) and hornworts (䊏) in Selvagens Archipelago and the other islands of Madeira Archipelago.

mosses have the lowest representativity (44 %), while hornworts are represented by four species (3 %). The different patterns of representation of liverworts and mosses may be explained by the distinct environmental conditions and variability of the habitats in the different islands of the Madeira Archipelago.

The 12 acrocarpous mosses found in the bryoflora of Selvagens Archipelago represent 75 % of its total bryoflora, followed by the thallose liverworts (3 taxa, representing 19 %), and only one pleurocarpous moss (Fig. 3). The acrocarpous mosses are included in three families, namely the Pottiaceae Schimp. (7 taxa), Bryaceae Schwägr. (3 taxa) and Fissidentaceae Schimp. (2 taxa), which are adapted to the xeric and saline conditions that prevail on Selvagens, as is the particular case of Tortula pallida.

A comparative analysis revealed that the proportion of the acrocarpous mosses in Selvagens is closer to the one observed for Desertas (51 %), followed by Madeira Island (47 %), but distinct from Porto Santo, where the foliose liverworts (37 %) are more highly represented than the acrocarpous mosses (32 %) (Fig. 3).

There is only one species of pleurocarpous mosses referred to Selvagens, namely, Heterocladium heteropterum. However, this taxon cited by Luiser (1942) to Selvagem Pequena is considered a doubtful species for that island, as it is generally associated with hygrophilous conditions that are not found in Selvagem Pequena habitats.

The Riccia spp. are the only liverworts able to develop in the unstable and xeric conditions of the Selvagens habitats (Fig. 3). In fact, the thallose liverworts occur also in the other Madeira

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Archipelago islands, revealing a lower incidence in Madeira Island, where the pleurocarpous mosses showed their highest representativity.

The topographical characteristics of Selvagens Archipelago determine a particular bryoflora composition, which distinguishes Selvagens from all other islands of Madeira Archipelago, more closely related concerning the proportion of the bryophyte groups considered. Of the 12 bryophyte taxa endemic to Madeira (Table 2), only one, Riccia atlantica SĂŠrgio & Perold, was found in Selvagens Archipelago. This species is also referenced to Porto Santo Island, extending the distribution to all islands of Madeira Archipelago (Table 2).

Phytogeographic affinities of the Selvagens bryoflora In order to analyse the differences in bryophyte species composition between the Selvagens Archipelago and the islands of Madeira and Canary Islands Archipelagos, a Cluster Analysis was performed (Fig. 4).

Five species were found to be present in all analysed islands, namelly Bryum dichotomum Hedw., Riccia sorocarpa Bisch., Tortella flavovirens (Bruch) Broth., Tortula atrovirens (Sm.) Lindb., and Tortula muralis Hedw. Although 13 of the 16 species present in Selvagens are in common with the Madeiran bryoflora, the strong xeric and saline ecological conditions of the Selvagens make its bryoflora quite distinct from the one found in Madeira Archipelago. The Madeira Archipelago bryoflora is very rich and diverse, and results from the existence of a high diversity of habitats, which are due to the particular geographical, geological and ecological conditions found mainly on Madeira Island. This diversity explains the great differences between

Fig. 4. Dendrogram showing the similarities between the bryoflora of Selvagens, Madeira and Canary Islands, based on species presence and absence data, using the options group average linkage and Euclidean distance.

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its bryoflora from the one observed on the other islands of the Madeira Archipelago, as well as from the bryoflora of Selvagens Archipelago and also from Canary Islands (Fig. 4). On Madeira Island most of the endemics with oceanic affinities are found, mainly liverworts with neotropical affinities (Sim-Sim et al. 2005; Stech et al. 2006, 2010; Vanderpoorten et al. 2007; Aigoin et al.

2009). The Paleo-endemic Echinodiaceae whose origins date back from the European Tertiary period (Stech et al. 2008) can also be included in this group. The highest representativity of taxa with Atlantic and Mediterranean Europe affinities is also found in Madeira Island, where habitat diversity and factors such as altitude (and thus climate) differ.

The bryoflora of Selvagens Archipelago is closest to the driest islands of Madeira Archipelago, namely Desertas and Porto Santo. These islands have seven species in common, namely Bryum dichotomum, Heterocladium heteropterum, Riccia atlantica, Riccia sorocarpa, Tortella flavovirens, Tortula atrovirens and T. muralis. It is closer, however, to the Desertas bryoflora, having one more species in common, namely T. solmsii. Concerning the Canary Islands, Selvagens bryoflora is closest to the bryoflora of Fuerteventura and Lanzarote, the two islands of the eastern group closer to mainland Africa. These islands are the oldest of the archipelago and present smaller altitudinal ranges. Their bryoflora is also the less rich of the Canary Islands Archipelago, and has ten species in common with the Selvagens bryoflora, namely Bryum canariense, B. dichotomum, Fissidens sublimbatus, Riccia lamellosa, Riccia sorocarpa, Tortella flavovirens, Tortula atrovirens, T. lanceolata R. H. Zander, T. muralis and T. solmsii.

Analysing the new data on the bryoflora of Selvagens, as well as Porto Santo (eight new taxa), a concordance was observed with the results obtained by GonzĂĄlez-Mancebo et al. (2008). However, future studies especially in the Island of Porto Santo may contribute to a better knowledge of its bryoflora and to clarify the proportion between mosses and liverworts.

Concluding remarks The lowest diversity of Madeira´s bryoflora occurs on the Selvagens Archipelago, which is under strong xerophytic and saline contraints due to its geographical position and climate. This definitely influences the composition and structure of the Selvagens bryophyte flora. The topographical characteristics as already mentioned by Nóbrega (1955) for the vascular plant vegetation, are also important, being characterised by premature growth, predominance of xerophytic characteristics, succulence, less chloroplasts, and the psammophilous or halophilous character of some species.

Nevertheless, the natural habitats of the Selvagens take on significant importance and value for the maintenance of biological diversity in the Macaronesian Region and consequently in the World. The animals and plants endemic to Selvagens are confined to an extremely restricted geographical area, which, according to present IUCN criteria, makes them inherently threatened.

Acknowledgements Thanks are due to the directors of the Natural Park of Madeira and the Selvagens Nature Reserve for the permission to land and to collect the plant material, as well as for the hospitality and help during the field work. Special thanks are owing to the Nature Warden Isamberto Silva for collecting bryophytes at the Selvagem Grande Island.

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