Analyses of the Colosseum's floristic changes during the last four centuries.

Different floristic lists of the Colosseum have been carried out starting from the XVII century (PANAROLI, 1643; SEBASTIANI, 1815; DEAKIN, 1855; FIORINI MAZZANTI, 1874; ANZALONE, 1951; and recently CELESTI GRaPOW et al., 2001). The comparison among these investigations reveals the rich plant colonisation, due to the great variety of habitats present in the monument and to its state of abandon. The maximum peak of 418 species can be referred in Deakin s list, and the minimum are the current 242 species, mainly distributed in the hypogeans. The total amount of colonising species in time was 684 vascular plants. The species listed for the monument in all the studies are 135, and all the common ones are 192. These are mainly herbaceous plants of ruderal habitats, widely distributed in more or less nitrophylous pastures or pioneer on rocks and walls. 426 species were enumerated before the XX century and later disappeared from the places. 117 species no longer belong to the Roman flora, and 24 species are no longer listed in the regional flora. These were mainly herbaceous and woody species typical of dynamically developed stages, belonging to forest and border line communities. Typical species of very disturbed habitats are also frequent. 66 species were cohected only in more recent times. These belong to the synanthropic flora, though tess nitrophylous compared with the previous, or are cultivated plants capable of becoming spontaneous under favourable conditions. The comparison among the different floras indicates not only the change in use of the monument, but also that climatic and microclimatic changes occurred in the last centuries. The relative biological and chorological spectra confirm the progressive warming and average reduction of humidity of the site.