The samples were collected by the ISEM paleoenvironment
team at the four sites following the same technique, i.e. care-
fully scraping the beds in order to prevent present-day pollen
contamination and immediately isolating the samples in ster-
ile plastic bags. Our study includes 25 samples (see sup-
plemental information). Mae Moh and Chiang Muan sam-
ples come from lignite deposits, whereas Nong Ya Plong
and Khorat samples come from organic-rich claystones. The
Chiang Muan site includes 4 samples partly published in
(Chaimanee et al., 2003) and 2 unpublished samples. The
samples were submitted to a four-step chemical treatment.
First, caustic potash (KOH 10%) was used to remove humic
acids 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 frag-
ments, and a final centrifugation with glycerine water was
carried out before mounting samples on microscope slides