No abstract

-(Vegetative propagation strategies of four rupestrian species of Leiothrix (Eriocaulaceae)). 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.

Aquatic plants exposed to environmental changes exhibit plastic responses, resulting in functional adjustments to reduce stress effects. Lack of light can limit plant development and can affect biomass allocation and reproduction, stressing plants and sometimes halting their growth. Shading techniques have been used to control the excessive growth of weed plants, such as the aquatic fern Salvinia auriculata Aublet that can form dense mats on the water surface, causing problems in water use. We used shading nets in a greenhouse experiment to evaluate the effect of shade on the biomass of S. auriculata, and to determine if the fern changes its allocation of biomass to sexual (sporocarps) or asexual (buds) reproduction under different shade levels (full-sun control, 35% shade, and 70% shade). Under shade conditions, ramet biomass decreased and no sporocarps were produced, although the number of buds increased. Production of structures for sexual reproduction incurs a high energy cost, so S. auriculata invested in bud production (clonal reproduction). The differing energy requirements resulted in a significant trade-off between bud and sporocarp production. In conclusion, our study indicated that shading is not an efficient control technique for S. auriculata since it did not affect the clonal reproduction, a strategy that accelerates colonisation and facilitates rapid spread.

No abstract

No abstract