Herbaceous floristic study and relationship with soil of crystalline shield and sedimentary basin caatinga areas at Petrolandia, Pernambuco State, Brazil

(Herbaceous floristic study and relationship with soil of crystalline shield and sedimentary basin caatinga areas at Petrolandia, Pernambuco State, Brazil). Floristic surveys were carried out in two close caatinga areas, one on the crystalline shield and the other on a sedimentary basin, both at Petrolandia, Pernambuco, Brazil, with the objective of identifying differences between the two areas in composition, habit and life form of the herbaceous flora. One hundred 1x1 m plots were established in each area and all the herbaceous species were identified. Soil samples were collected at 0-20 and 20-40 cm depths. In general, the soil in the crystalline shield area was shallower, had greater clay content, with higher water holding capacity, and was more fertile. The number of families, genera and species in the sedimentary basin and crystalline shield areas were 32, 62 and 78 and 31, 53 and 69, respectively. The floristic similarity between the areas was high (75%). The clustering analysis showed that the floristic arrangements between the sampled plots are more similar within the areas than between areas, suggesting the existence of distinct groups. Soil type seems not to be a factor determining the floristic similarity, habit or life forms of the caatinga vegetation herbs when the areas are near, but it may influence the occurrence and the frequency of some species.