You can credit the database in published work that makes use of results from CLOPLA1, citing CLOPLA1 as an electronic publication. Here is one possible form for an entry:
Klimešová J. & Klimeš L. & 1998. CLOPLA1 (CLOnal PLAnts, version 1) - a database of clonal growth in plants of central Europe. published at <http://www.butbn.cas.cz/klimes/>
You can also refer to the following publication, giving details about the database and some examples of its utilisation:
Klimeš L., Klimešová J., Hendriks R. & van Groenendael J. 1997. Clonal plant architectures: a comparative analysis of form and function. In: H. de Kroon & J. van Groenendael (Eds.): The ecology and evolution of clonal plants. Backhuys Publishers, Leiden, the Netherlands, 453 pp., pp. 1-29.