We have cloned and characterised a highly repetitive DNA family that represents about 5% of the nuclear genome of Zamia paucijuga, a member of Cycadales, an ancient and rare group of seed plants. The unit repeat, cloned from EcoRV digested genomic DNA, has a length of about 323 bp, an high GC content (65-70%) and a subtelomeric localisation. The DNA of Z. paucijuga was digested with various restriction enzymes and analysed by Southern blot using the cloned unit repeat as a probe. These experiments indicated that the repeat is present in the plant genome in an unusual organisation, as tandem arrays typical of satellite DNA and as dispersed elements. The characterisation of these unusual "dispersed satellite DNA" elements required a complex series of experiments using combined Southern blot analyses, PCR, cloning and sequencing. Our results indicate that most of these dispersed elements are formed by few units of the GC-rich satellite DNA repeats arranged in tandem and flanked at both sites by one copy of a 0.6 kb AT-rich direct repeat. This unusual satellite DNA organisation of GC-rich repeats is present in many species of genus Zamia, and, thus, likely represent an ancient rearrangement of the satellite DNA repeats that spread in the genome as dispersed elements.