Melocactus

Abstract: Melocactus glaucescens (Cactaceae) is a critically endangered species endemic to northeastern Brazil. It grows in sympatry with other congeneric species and there is evidence for hybridization among them. We evaluated the levels of genetic and morphological variability and their substructuring between populations of M. glaucescens and sympatric species, and we tested for the occurrence of natural hybridization. Genetic variability was investigated using 12 allozyme loci, and morphological variability was investigated using multivariate morphometric analyses of 18 vegetative characters in nine natural populations of M. glaucescens , Melocactus ernestii , Melocactus concinnus and two distinct morphs of putative hybrids ( Melocactus ¥ albicephalus ). Genetic variability was low in all populations ( P = 7.7–41.7, A = 0.3–1.7, H e = 0.009–0.096), and all taxa displayed a deficit in heterozygotes. Low genetic structuring and moderate morphological structuring were found for M. glaucescens ( F ST = 0.045, A MRPP = 0.16) and M. concinnus ( F ST = 0.022, A MRPP = 0.11). The results obtained are inconclusive with respect to confirming the hypothesis of occurrence of hybridization because of an absence of diagnostic loci in the presumed parental species. The presence of several private alleles and the absence of linkage disequilibrium in the putative hybrids indicate that M. albicephalus should be treated as a distinct species, and not given hybrid status as recently stated by a number of authors. The large number of exclusive alleles and the levels of morphological structuring in the populations of M. glaucescens are important factors that need to be considered in the definition of strategies for the conservation of this species.

Abstract: The seeds from different species present variable behavior for temperature and substratum in the germination process, and this can provide information of biological and ecological interest. In relation to the tropical species, there is insufficient knowledge about the requirement of the seed when it is related with the different factors involved in the germination. In this way, the objective of this paper was to evaluate the influence of the temperature and substratum in the germination of Melocactus bahiensis seeds. The germinations were analyzed in constant temperatures of 20, 25 and 30 oC, and alternated temperatures of 20-30 oC in sand and filter-paper substratum. The variables evaluated were the germination speed index, percentage of germination and the height of the aerial part of seedling. The highest percentage of germination and germination speed index were at 25 oC and there were not differences between the substrates tested. For the height of the aerial part of seedling, the results showed that there was not variation in function of the temperature for the sand substratum, being the averages higher than the filter-paper substratum. The best conditions for the conduction of germination test of Melocactus bahiensis’s seeds are sand substratum and temperature of 25 oC.