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We studied the flora of vegetation islands on rock outcrops on the Itatiaia Plateau (22°21'S and 44°40'W), at 2,400 m.a.s.l. A total of 114 vascular plant species, which correspond to ca. 20%-25% of the currently inventoried flora of the plateau, were sampled in 197 small vegetation islands (total area of 0.034 ha). Xerophytes and hydrophytes were often found side by side due to environmental heterogeneity at a small scale, explaining in part the high species diversity. Rock outcrops may support floras quite distinct from those in neighbouring habitats, due to the action of strong environmental filters, but in Itatiaia the geographic distribution patterns among rupicolous plants appear to mimic those described for the whole flora around it, with 15.1% of narrow endemic species and six strictly rupicolous plants. Underlining the "temperate" nature of the high elevation climate in Itatiaia, the sampled flora was dominated by species of the families Asteraceae and Poaceae, and the number of CAM (crassulacean acid metabolism) species was very low. A few endemic species of tropical origin - Pleurostima gounelleana (Beauv.) Men. (Velloziaceae) and Fernseea itatiaiae (Wawra) Baker (Bromeliaceae) - play a crucial role in this vegetation, as pioneer mat-formers facilitating later establishment of numerous other species. Hemicryptophytes prevail in the sampled flora, while therophytes are exceptionally rare and mainly consist of opportunistic species associated with disturbances. Numerous microhabitats and strong environmental gradients in these high elevation rock outcrops afford opportunities for establishment of a highly diversified flora. These island-like environments may represent an important refuge for grassland species from fire and other disturbances in the surrounding grasslands.

An area's innate potential to regenerate represents a crucial factor for its conservation and management. The seed rain and seed bank are important agents in the regeneration process. Seed banks are particularly important in communities where there is a high proportion of obligate seeders. Rocky outcrops are habitats where most part of the plant species depends on their seeds to reproduce and maintain viable populations. Therefore, seed banks ought to be important in this vegetation physiognomy. We test the hypotheses that the seed bank of the rocky outcrops found in the rupestrian fields of "Serra do Cipó", Brazil, is richer in species and denser than those formed on different vegetation physiognomies neighboring the outcrops. We then compared species abundance, species richness and composition in the rocky outcrops' seed banks with those of sandy and peaty bogs, forests, gallery forests, and "cerrados". Furthermore, we report on the natural regeneration potential of these soils by assessing a greenhouse study on seedling emergence. Soil samples were collected from 0 to 5 and 5 to 10 cm of depth. Rocky outcrops had the poorest in species and less dense seed bank and showed segregation in species composition. Emergence was greater in the most superficial layer. However, soils on rocky outcrops showed the greatest proportion of endemic threatened species in their seed banks, demonstrating their importance for biodiversity conservation of the "Serra do Cipó" rupestrian fields. O potencial nato de uma área regenerar após um distúrbio é um fator crucial para sua conservação e manejo. A chuva e o banco de sementes são agentes importantes dessa regeneração. Bancos de sementes são particularmente importantes em comunidades onde a proporção de espécies com reprodução estritamente por sementes é alta. Nesses casos, o banco de sementes é a principal via de regeneração. Afloramentos rochosos são ambientes onde a maior parte das espécies dependem de sementes para reproduzir e manter populações viáveis. Assim, testamos a hipótese de que os afloramentos rochosos da Serra do Cipó teriam solos com bancos de sementes mais ricos e densos do que as outras fisionomias vegetacionais adjacentes. Comparamos então a abundância, riqueza e composição de espécies dos bancos de sementes dos solos dos afloramentos rochosos com os dos brejos arenosos e turfosos, capões de mata, matas de galeria e cerrados. Avaliamos a regeneração natural através da emergência de plântulas. O solo foi coletado entre 0 e 5 cm e entre 5 e 10 cm de profundidade. Os afloramentos rochosos apresentaram os bancos menos densos e mais pobres em espécies, sendo a emergência de plântulas maior nas camadas mais superficiais do solo. Entretanto, a proporção de espécies endêmicas e ameaçadas foi maior, demonstrando que esses solos são importantes para a conservação da biodiversidade dos campos rupestres da Serra do Cipó.

We studied the flora of vegetation islands on rock outcrops on the Itatiaia Plateau (22°21'S and 44°40'W), at 2,400 m.a.s.l. A total of 114 vascular plant species, which correspond to ca. 20%-25% of the currently inventoried flora of the plateau, were sampled in 197 small vegetation islands (total area of 0.034 ha). Xerophytes and hydrophytes were often found side by side due to environmental heterogeneity at a small scale, explaining in part the high species diversity. Rock outcrops may support floras quite distinct from those in neighbouring habitats, due to the action of strong environmental filters, but in Itatiaia the geographic distribution patterns among rupicolous plants appear to mimic those described for the whole flora around it, with 15.1% of narrow endemic species and six strictly rupicolous plants. Underlining the "temperate" nature of the high elevation climate in Itatiaia, the sampled flora was dominated by species of the families Asteraceae and Poaceae, and the number of CAM (crassulacean acid metabolism) species was very low. A few endemic species of tropical origin - Pleurostima gounelleana (Beauv.) Men. (Velloziaceae) and Fernseea itatiaiae (Wawra) Baker (Bromeliaceae) - play a crucial role in this vegetation, as pioneer mat-formers facilitating later establishment of numerous other species. Hemicryptophytes prevail in the sampled flora, while therophytes are exceptionally rare and mainly consist of opportunistic species associated with disturbances. Numerous microhabitats and strong environmental gradients in these high elevation rock outcrops afford opportunities for establishment of a highly diversified flora. These island-like environments may represent an important refuge for grassland species from fire and other disturbances in the surrounding grasslands. O objeto deste estudo foi a flora que se distribui em ilhas de vegetação isoladas sobre a superfície rochosa, no Planalto do Itatiaia (22°21'S e 44°40'W), a 2.400 m de altitude. Foi encontrado um total de 114 espécies vasculares, correspondendo a ca. 20%-25% da flora total atualmente inventariada do Planalto, em 197 pequenas ilhas de vegetação (área total de 0,034 ha). Xerófitas e hidrófitas com freqüência ocorrem lado a lado devido à forte heterogeneidade ambiental em pequena escala espacial, explicando em parte a alta diversidade local. Superfícies rochosas podem abrigar floras muito distintas do entorno em função de fortes filtros ambientais contrastantes, mas no Itatiaia os padrões de distribuição geográfica de plantas rupícolas assemelham-se aos dos campos no entorno, com 15,1% das espécies sendo endêmicas restritas e seis sendo estritamente rupícolas. Destacando a natureza "temperada" do clima de altitude do Itatiaia, a flora estudada foi dominada por espécies de Asteraceae e Poaceae, e o número de espécies CAM (metabolismo ácido das crassuláceas) foi muito baixo. Algumas endêmicas restritas de origem tropical - Pleurostima gounelleana (Beauv.) Men.(Velloziaceae) e Fernseea itatiaiae (Wawra) Baker (Bromeliaceae) - formam tapetes sobre a rocha e são fundamentais para o estabelecimento de ampla gama de espécies. Hemicriptófitas predominam na flora amostrada, enquanto terófitas são excepcionalmente raras e consistem, principalmente, de espécies oportunistas associadas com distúrbio. Os numerosos microhábitats e os marcantes gradientes ambientais nestes afloramentos de altitude elevada criam oportunidades para o estabelecimento de uma flora muito diversificada. Estes ambientes insulares parecem constituir importante refúgio para as espécies dos campos em geral, frente a perturbações como incêndios e outras ações antrópicas.

Plant establishment and growth on rocky outcrops in the Itatiaia massif (2400 m a.s.l.), southeastern Brazil, are limited by lack of soil and by freezing temperatures in winter nights. Mat-forming species of different sizes and shapes on bare rock provide substrate for other plants to establish. The habitat preference of two geophytes, Stevia camporum (Asteraceae) and Alstroemeria foliosa (Alstroemeriaceae), was compared with regard to their association with the type of mat species and distinct rock topographies. The habitat preference of the mat species in regard to topography was also assessed. We found 1706 ramets of S. camporum and 1317 of A. foliosa in 253 vegetation islands ranging in size from 0.005 to 18.097 m 2 . Mat species in these islands were Fernseea itatiaiae, Vriesea itatiaiae (both Bromeliaceae), Pleurostima gounelleana (Velloziaceae) and/or Campylopus pilifer (Dicranaceae) and other mosses. Mat species were segregated by topography. Geophytes were similarly distributed across types of topography but showed negative interspecific association. S. camporum occurred mostly on the moss-dominated islands, whereas A. foliosa was more common in P. gounelleana islands. We found geophyte co-occurrence in larger vegetation islands containing both P. gounelleana and mosses as mat species. Thus, the effect of topography on geophyte segregation was indirect, since topography affects mat species distribution, and the geophyte preference for distinct mat species as substrate resulted in their segregation.