Thesamples were submitted to a four-step chemical treatment.First, caustic potash (KOH 10%) was used to remove humicacids and plant matter. The samples were filtered through a 180 µm mesh and centrifugated several times (Faegri et al.,1989). Then, the residues were treated with Hydrofluoric Acid (HF) to remove mineral elements. Finally, acetolysis
was performed to get rid of possible remaining plant fragments, and a final centrifugation with glycerine water was
carried out before mounting samples on microscope slides