THE DIVERSITY OF SEGETAL WEEDS IN CRETE (GREECE) ATSPECIES AND COMMUNITY LEVEL

Based on a data set of 74 relevés of cereal fields treated without application of herbicides and fertilizers, the Cretan segetal weed flora and vegetation is analysed. The species pool on the fields comprises almost 20 % of the total flora of Crete although only about 5% occur more commonly as segetal weeds. While most species accur in a wider range of synanthropic (sub)nitrophytic habitats or semi-natural formations such as phrygana, woodlands and semiwet meadows, a total of 33 species are exclusive weeds of traditional agriculture. The latter inclde annual species but also a considerable number of geophytes. Several such obligate weed taxa found only in one or few fields atre threatend from a regional extinction. Two segetal species last recorded 100 yeras ago have not been confirmed. Oxalispes-capreae is the only alien wwed within the last decades that successfully invaded Cretan cereal fields. By means of classification of relevés using floristic criteria 7 plant community types were identified and assigned to three associations (with additional sub-types). Species composition, distribution and ecology of the community types are described and the syntaxonomic and biogeographical relations discussed.