An updated inventory of the native vascular flora of Italy, providing details on the occurrence at regional level, is presented. The checklist includes 8195 taxa (6417 species and 1778 subspecies), distributed in 1092 genera and 152 families; 23 taxa are lycophytes, 108 ferns and fern allies, 30 gymnosperms and 8034 angiosperms. The taxa currently occurring in Italy are 7483, while 568 taxa have not been confirmed in recent times, 99 are doubtfully occurring in the country and 19 are data deficient. Out of the 568 not confirmed taxa, 26 are considered extinct or possibly extinct.

An updated inventory of the vascular flora alien to Italy, providing details on the occurrence at regional level, is presented. The checklist includes 1597 species, subspecies, and hybrids, distributed in 725 genera and 152 families; 2 taxa are lycophytes, 11 ferns and fern allies, 33 gymnosperms, and 1551 angiosperms. 157 taxa are archaeophytes and 1440 neophytes. The alien taxa currently established in Italy are 791 (570 naturalized and 221 invasive), while 705 taxa are casual aliens, 4 are not assessed, 7 are of unknown regional distribution, 47 have not been confirmed in recent times, 3 are considered extinct or possibly extinct in the country, and 40 are doubtfully occurring in Italy. This checklist allows to establish an up-to-date number (9792) of taxa constituting the whole (native and alien) Italian flora.

The census of the loci classici of 1,400 Italian endemic vascular plants (i.e. not thriving elsewhere with the exception of Corsica and Malta) is here presented and described. The effective place of publication of accepted names, basionyms and homotypic synonyms were identified and critically verified. This often resulted in some change in authorship attribution and, in seven cases, in validation problems (Asperula cynanchica var. lactea var. nov., A. lactea comb. nov., Biscutella laevigata subsp. raffaelliana subsp. nov., Ferulago nodosa subsp. geniculata comb. & stat. nov., Limonium tineoi comb. nov., L. usticanum sp. nov., Noccaea torreana comb. nov.). The geographic information on the loci classici was excerpted from the protologues, as well as information on typification for the taxa described before 1 January 1958. The names without holotype are 796. For 347 names a lecto- or neo-typification is available in literature, while 449 currently accepted taxa still need of type designation.

A taxonomic revision of the genus Amaranthus (Amaranthaceae) in Italy is here presented. Field surveys were carried out during the period 2006–2014. 58 herbaria (both European and American, including 12 personal herbaria) were consulted (more than 3,000 specimens were examined) as well as extensive literature was analized. Twenty-seven non-hybrid taxa (twenty-four species, and six varieties) are recognized (A. crassipes and A. graecizans subsp. graecizans are considered doubtful for the flora of Italy). Three taxa (A. blitum, A. cacciatoi, and A. graecizans subsp. sylvestris) are native, one (A. bouchonii) has doubtful origin, while the others are to be considered aliens, mostly neophytes native to the Americas. Information about nomenclature (accepted names, main synonyms, and types), morphology, chromosome number, chorology (for native taxa) or alien status (for exotic taxa, at national and regional levels), occurrence in Italy (at regional scale), ecology (preferential habitat, phenology, elevation), taxonomic annotations are provided for each taxon, as well as original photos were prepared. Diagnostic keys at species and infraspecific levels (for A. blitum subsp. blitum s.l., A. emarginatus s.l., and A. graecizans s.l.) are given. An isolectotype for the name A. bouchonii was found at Z. A list of the seven hybrids recorded and their main morphological characteristics are also given. Among them, A. × mauritii is recorded in the present study for the first time in Italy. The nomenclatural change Amaranthus × pyxidatus comb. et stat. nov. is proposed. Two specimens preserved at MPU are designated as lectotype and isolectotype of the name A. × mauritii s.s., while for A. × mauritii f. ramosissima the holotype was found; the two names are to be considered heterotypic synonyms (new synonymy).

In this contribution, new data concerning the distribution of vascular flora alien to Italy are presented. It includes new records, confirmations, exclusions, and status changes for Italy or for Italian administrative regions of taxa in the generaAcalypha,Acer,Canna,Cardamine,Cedrus,Chlorophytum,Citrus,Cyperus,Epilobium,Eucalyptus,Euphorbia,Gamochaeta,Hesperocyparis,Heteranthera,Lemna,Ligustrum,Lycium,Nassella,Nothoscordum,Oenothera,Osteospermum,Paspalum,Pontederia,Romulea,Rudbeckia,Salvia,Sesbania,Setaria,Sicyos,Styphnolobium,Symphyotrichum, andTradescantia. Nomenclature and distribution updates, published elsewhere, and corrigenda are provided as supplementary material.