Struthanthus flexicaulis is a hemiparasite abundant in ironstone outcrops in southeast Brazil. We evaluated its host preference among species of the plant community, taking into account the abundance and foliage cover of the hosts. The importance of each species in the community and the mortality caused by the parasite were assessed based on a quantitative survey in 10 strips measuring 1m x 50m. The 10,290 individuals belonged to 42 species. Only 15 had a relative abundance in the plant community greater than 1%, of which 12 showed vestiges of parasitism. More than 80% of deaths in the community were associated with parasitism. Non-infected individuals had significantly less mortality rates (7%) than those infected (83%) (²= 1102.4, df = 1, p < 0.001). The observed infestation was different from the expected both regarding relative host abundance (²= 714.2, df = 11, p<0.001) and foliage cover (²= 209.2, df = 11, p<0.001). Struthanthus flexicaulis preferredMimosa calodendron, a legume attractive to avian seed dispersers. The interaction is maintained and intensified not only by the birds, who deposit innumerous seeds on the hosts branches, but also very likely by the ability of M. calodendron to fix nitrogen, thereby enhancing the mistletoe's development.

In the Cerrado Biome of Brazil, African grasses constitute a serious problem, occurring in virtually all protected areas. Molasses grass (Melinis minutiflora P. Beauv.) accumulates more biomass than do most other species of the herbaceous stratum vegetation native to the Cerrado. In this study, our aim was to determine the impact of M. minutiflora on native vegetation, as well as (using simulations of fire traits) on the characteristics of fires, in invaded areas of the Serra do Rola-Moça State Park (Parque Estadual da Serra do Rola-Moça, PESRM), a protected area where fires are frequent, in the state of Minas Gerais, Brazil. Our main results are that M. minutiflora considerably increases the amount of biomass, becoming the main combustible plant in the campo-cerrado (grassy-woody savanna) fires in the PESRM; that the native monocot biomass is inversely correlated with the M. minutiflora biomass, suggesting suppression of the native herbaceous stratum; that eudicots are diminished by M. minutiflora, both in number of individuals and number of species; and that fires are more severe in M. minutiflora-invaded areas.

As plantas parasitas (ervas-de-passarinho) podem alterar o crescimento, reprodução e fisiologia das hospedeiras. Mimosa calodendron (Fabaceae) é uma leguminosa abundante nos campos rupestres sobre canga, freqüentemente atacada pela hemiparasita Struthanthus flexicaulis (Loranthaceae). O objetivo deste trabalho foi avaliar as conseqüências do parasitismo de S. flexicaulis na aptidão de M. calodendron. Foram avaliadas a intensidade de parasitismo e mortalidade em mimosas de diferentes tamanhos, e comparadas a cobertura foliar e a produção de frutos e sementes em indivíduos parasitados e não parasitados. Mais de 65% da população de 1.820 indivíduos estavam parasitados. A densidade de mimosas influenciou positivamente o parasitismo. As taxas de parasitismo e de mortalidade foram maiores nas mimosas de maior porte. As plantas hospedeiras muito parasitadas apresentaram de 75 a 95% de redução da cobertura foliar e sua produção de frutos foi cerca de 25% das não parasitadas. Embora não tenha sido detectada diferença estatística no número de sementes produzidas por vagem, o peso das sementes foi menor nas mimosas parasitadas. O parasitismo por S. flexicaulis, por reduzir as taxas de sobrevivência e fecundidade de M. calodendron, pode modificar sua estrutura e dinâmica populacional.

Parasitic plants (mistletoes) may alter the growth, reproduction and physiology of their hosts. Mimosa calodendron (Fabaceae) is a legume abundant in rupestrian fields on ironstone outcrops, frequently attacked by the hemiparasite Struthanthus flexicaulis (Loranthaceae). The objective of this study was to evaluate the consequences of parasitism by S. flexicaulis on the fitness of M. calodendron. The intensity of parasitism and mortality on hosts of different sizes was evaluated, and foliage cover, fruit and seed set in parasitized and non-parasitized individuals were compared. More than 65% of a population of 1820 individuals was attacked. Host density positively influenced parasitism. The mortality and number of attacked hosts increased with their crown diameter. Heavily parasitized individuals showed 75 to 95% reduction of leaf cover and fruit production of 25% of those non-parasitized. Although no statistical difference was detected between the number of seeds per fruit, seed weight was lower in attacked plants. Parasitism by S. flexicaulis on M. calodendron may alter its population structure and dynamics, by reducing survival and fecundity rates.

Leiothrix é endêmico da América do Sul e inclui 37 espécies, 25 das quais ocorrem em Minas Gerais, 19 delas na Serra do Cipó. Descrevemos as estratégias de propagação vegetativa em quatro espécies de Leiothrix, endêmicas à porção mineira da Cadeia do Espinhaço. Para cada espécie estabelecemos parcelas permanentes, marcamos de 30 a 51 rosetas ou clones e tomamos medidas morfológicas e fenológicas. Leiothrix crassifolia (Bong.) Ruhland e L. curvifolia var. lanuginosa (Bong.) Ruhland são rizomatosas e formam clones compactos do tipo falange. Leiothrix vivipara (Bong.) Ruhland não produz rizomas, mas é pseudovivípara, produzindo numerosos rametes originários da inflorescência. Esses rametes são formados precocemente, sem os capítulos tocarem o solo. Leiothrix spiralis (Bong.) Ruhland possui as duas formas de crescimento clonal: é rizomatosa e pseudovivípara. Nesta espécie, os rametes são formados tardiamente, somente depois do capítulo tocar o solo. Uma das condições típicas dos campos rupestres é a escassez de água no solo em alguns períodos do ano, além da escassez de nutrientes durante todo o ano. Estas condições podem ter criado um cenário ecológico ideal para a evolução de pseudoviviparidade e do crescimento rizomatoso em Leiothrix.

Leiothrix is endemic of South America and includes 37 species, 25 of which occur in the state of Minas Gerais. Nineteen of those occur in the "Serra do Cipó", a mountain chain, located in the southern portion of the Espinhaço mountain range. This study examines vegetative propagation strategies of four species of Leiothrix, endemic to the Minas Gerais portion of the Espinhaço mountain range. For each species we established permanent plots, where we marked 30 to 51 rosettes or clones, and then took morphological and phenological measurements. Leiothrix crassifolia (Bong.) Ruhland and L. curvifolia var. lanuginosa (Bong.) Ruhland are rhizomatous, forming compact clones. Leiothrix vivipara (Bong.) Ruhland does not produce rhizomes, but is pseudoviviparous, i.e., produces numerous ramets originating from inflorescences. These ramets are formed precociously, and the flower heads do not touch the ground. In Leiothrix spiralis (Bong.) Ruhland both of these strategies are seen: it is both rhizomatous and pseudoviviparous. In this species, the ramets are formed late, only after the flower head has touched the ground. One of the typical conditions of the rupestrian grasslands is soil water shortage in some periods of the year and nutrient scarcity all year round. These conditions might have created an ideal ecological scenario for the evolution of both pseudovivipary and rhizomatous clonal growth in Leiothrix.

Leiothrix flagellaris é uma pequena planta clonal que se desenvolve em solos arenosos/pedregosos e pobres em nutrientes dos campos rupestres do sudeste do Brasil. Durante a estação chuvosa, a maioria dos seus capítulos se transforma em rosetas geradas por pseudoviviparidade e que são ligadas à planta-mãe por hastes flexíveis que continuam seu crescimento e alcançam até cerca de 90cm. A maioria destas rosetas permanece suspensa sobre pedras ou sobre a rala vegetação herbácea local, enquanto que uma pequena fração toca o solo e se enraíza. Estas rosetas suspensas alcançam tamanhos comparáveis ao de rosetas enraizadas e produzidas nas estações reprodutivas precedentes e que já se reproduzem. À medida que as rosetas enraizadas crescem, seu potencial de gerar e dispersar novas rosetas pseudovivíparas aumenta rapidamente. A estratégia de crescimento guerilha de L. flagelaris parece reunir características que permitem rápido incremento da área fotossintética e elevam as chances de recrutamento, provavelmente reduzindo insucessos na dispersão e estabelecimento em seu severo ambiente.

Leiothrix flagellaris is a small clonal plant that grows in sandy/rocky, nutrient poor soils in the rocky grasslands ("campos rupestres") of southeastern Brazil. In the rainy season most of their flower heads differentiate into small rosettes, produced by pseudovivipary, and connected to the mother-plant by flexible, elongated stalks that can reach up to 90cm. Most of these rosettes remain suspended over rocks or over the sparse herbaceous surrounding vegetation, while a few arch low enough to come into contact with the surrounding soil and take root. These suspended rosettes can reach diameters comparable to currently rooted and reproductively active rosettes produced during previous reproductive periods. As the rooted rosettes grow up, their potential to generate and disperse new pseudoviviparous rosettes increase rapidly. This unusual guerrilla strategy of L. flagellaris seems to congregate a suit of traits that promote a fast increase in photosynthetic area and improve recruitment, thereby helping to circumvent dispersal and establishment failures in its severe environment.