Occurrence and ecological characteristics of C4 dicot and Cyperaceae species in the Hungarian flora.
The wild flora of Hungary (except grasses) was screened for C4 plants by using the stable carbon isotope ratio, the leaf anatomy and the photosynthetic carbon dioxide compensation concentration. Thirty-one C4 species (native or naturalized) were found in the Amaranthaceae, Chenopodiaceae, Cyperaceae, Euphorbiaceae, Portulacaceae and Zygophyllaceae. Together with the 26 C4 grasses previously reported, a total of 57 wild C4 species were found in Hungary, comprising 2.6% of the country's angiosperm flora. The C4 species were predominantly annuals growing in open habitats such as dry grasslands, inland saline areas, temporarily exposed river beds and disturbed sites. The C4 species had higher temperature and light requirements, and their phenology lagged behind that of C3 plants. It is suggested that these differences may account for C4 plants being usually excluded from productive biotopes in Hungary, where the C3 canopy became closed during the growing season before C4 plants began their development. Ecological properties of C3 and C4 plants differed considerably in the Cyperaceae, but much less in the Chenopodiaceae. Among the C4 annuals, naturalized aliens were common. An increasing preponderance of C4 plants is considered likely as a result of climatic change and the impact of humans on terrestrial vegetation.