A phytogeochemical survey of the flora of ultramafic and adjacent normal soils in North Morocco

Variation in plant elemental composition (Ni, Ca, Mg, Mg/Ca ratio) in relat ion to soil composition was investigated in a poorly studied ultramafic are a in the north of Morocco. A total of 142 leaf samples representing 36 spec ies from 9 sites (5 ultramafic and 4 normal soils from adjacent areas) were analysed. The soil was richer in Mg and Ni and had a higher Mg/Ca ratio in the ultramafic sites than in the control sites, and these differences were qualitatively reflected in the average mineral composition of the plants. However, there were considerable differences in mineral composition among s pecies within serpentinic sites, indicating that species with contrasting m ineral nutrition strategies can cope with the mineral element imbalance cha racteristic of ultramafic soils. Particularly noteworthy was the finding th at species with high requirements of Ca are not excluded from serpentinic s oils. In view of their high responsiveness to soil nickel and magnesium con centration, Dittrichia viscosa and Lavandula dentata are proposed as bioind icators of these elements in the soil in the Rif area. By contrast, two loc al serpentine endemics, Halimium atriplicifolium and Notholaena marantae we re excluders of nickel and magnesium.