Occurrence and ecological characteristics of C4 dicot and Cyperaceae species in the Hungarian flora

The non-graminaceous wild flora of Hungary was screened for C₄ plants by using the stable carbon isotope ratio, the leaf anatomy and the photosynthetic carbon dioxide compensation concentration to determine the photosynthetic pathway type. On the whole, 31 C₄ species (native or naturalized) were found in the Amaranthaceae, Chenopodiaceae, Cyperaceae, Euphorbiaceae, Portulacaceae and Zygophyllaceae families. Together with the 26 C₄ grass species (Poaceae) reported earlier (Kalapos 1991), a total of 57 wild C₄ species occur in Hungary, which forms 2.6 % of the country's angiosperm flora. This figure is somewhat higher than what was expected on climatic grounds, a fact probably due to certain edaphic conditions favouring C₄ plant growth. In Hungary, the C₄ species are predominantly annuals growing in open habitats such as dry grasslands, inland saline areas, temporarily exposed riverbeds and disturbed sites. In comparison with C₃ plants, the C₄ species have higher temperature and light preferences, and their phenology lags behind that of the C₃ plants. These differences might account for C₄ plants being usually excluded from productive biotopes in Hungary, where the C₃ canopy may become closed during the growing season before C₄ plants can start their ontogenetic development. Ecological properties of C₃ and C₄ plants differ considerably in the Cyperaceae, but much less in the Chenopodianceae family. Among C₄ annuals naturalized aliens are common, most of which colonized hungary in the last two centuries. Increasing preponderance of C₄ plants is anticipated in the future as a consequence of possible climate changes and the ever increasing human impact on terrestrial vegetation. This revised version was published online in August 2006 with corrections to the Cover Date.