A comprehensive checklist of vascular flora occurring in the lower Sieve Valley basin (province of Florence, Tuscany) is presented. Despite its economic and agricultural significance, this territory has been largely overlooked by botanists, resulting in a substantial gap in floristic information. The checklist is based on bibliographic analysis and field studies carried out between 2018 and 2024. A total of 1034 spontaneous taxa (species and subspecies), including 141 aliens, are reported for the territory. Of these, 21 taxa represent new records or confirmations for the province of Florence and 893 taxa are new to the lower Sieve Valley. Tilia americana L. and Sequoia sempervirens (D.Don) Endl. are newly reported for Tuscany and Populus × canadensis Moench nothosubsp. canadensis should be considered as a naturalized alien in the region. Life forms and chorotypes exhibit pronounced Eurosiberian affinities, with a significant contribution from Mediterranean plants. This pattern aligns with the temperate and continental climate of the area, which is partially influenced by summer aridity.

Alien species, biodiversity, endemics, floristic data, Italy, phytogeography, Tuscany

Quantifying biodiversity is a primary objective for the scientific community, with plant diversity being of fundamental importance for achieving this goal (Kier et al. 2005). Floristic research serves as a foundation for biodiversity conservation efforts, and comprehensive floristic knowledge of a territory is essential for numerous applications in plant science (Peruzzi 2018). Unfortunately, these time-demanding activities are in decline, despite their crucial role in understanding and preserving our natural heritage (Prather et al. 2004). In floristic research, it is highly advisable to formulate an initial hypothesis regarding the expected number of taxa in a study area to guide field activities and contextualize the results obtained. To this end, Species-Area Relationships (SARs) serve as an excellent tool (D’Antraccoli et al. 2019, 2024).

The lower Sieve Valley (Tuscany, central Italy; Fig. 1) connects relevant areas of Tuscany: the Florentine Hills to the west, Mugello to the north, Casentino to the east, and Valdarno to the south. This strategic location enhances its significance fostering economic and cultural interactions among these diverse geographical areas. Additionally, this region is of remarkable viticultural importance, encompassing one of the seven subzones of Chianti Classico DOCG production, known as “Chianti Rufina” (D. Interm. July 31, 1932).

Figure 1. 

Localization and delimitation of the lower Sieve Valley (province of Florence, Tuscany). The black line defines the limit of the study area. The different shades of colors identify areas at different elevations ranging from 90 m to 992 m a.s.l. The Sieve River and the main streams are illustrated in blue. The image was obtained by means of Cartoteca del Geoscopio della Regione Toscana (http://www502.regione.toscana.it/geoscopio/cartoteca.html).

Despite its proximity to the city of Florence and the intense floristic research concentrated in this province over the past two decades (Ferroni et al. 2004; Viciani et al. 2008; Gestri and Peruzzi 2013; Gei et al. 2016; Selvi et al. 2016; Roma-Marzio et al. 2020; Gestri et al. 2023; Peruzzi 2023), the territory of the lower Val di Sieve has been largely overlooked by botanists over time, resulting in a lack of floristic information.

The first floristic records for the lower Sieve Valley were reported by Caruel (1860) and subsequently supplemented by Baroni (1897–1908). In the last century, Piussi (1962) conducted a silvicultural study, providing some floristic information for the artificial conifer plantations of the area. The most significant contribution is a popular botanical guide produced for the municipality of Pontassieve (Sartini and Mantovani 1993), although it was primarily conceived for educational purposes and lacks precise information on the localization of the reported taxa. Few additional floristic information can also be derived from Romolini (2001), Lombardi et al. (2002), Romolini and Sodi (2009) and Arrigoni (2020). Overall, between 1860 and 2010, only 140 taxa can be referred to the lower Sieve Valley, with 70 of them reported before 1950, mainly in studies not focused on extensive floristic exploration of this area.

Relative to the predicted richness based on Species-Area Relationships (SARs), the correspondence between the expected and observed number of established taxa is nearly exact (99.3%). This indicates a high level of floristic diversity in the lower Sieve Valley, comparable to other regions in Tuscany (D’Antraccoli et al. 2019). Alien taxa exceed expectations by 22%. Consequently, the study area has a relatively high number of aliens, albeit proportionally lower than other nearby areas like the Cerbaie Hills (+53%) and the municipality of Empoli (Peruzzi 2023, +207%). Notably, among the aliens, Ailanthus altissima (Mill.) Swingle and Ludwigia peploides (Kunth) P.H.Raven subsp. montevidensis (Spreng.) P.H.Raven are listed under European regulation EU 2019/1262 although the most widespread alien species in the area are Arundo donax L. and Robinia pseudoacacia L., as evidenced by a recent and extensive monitoring conducted on the Tuscan road network for these species (Pinzani and Ceschin 2023).

Four species recorded in the lower Sieve Valley during this study represent novelties or confirmations at the regional level: Zannichellia peltata Bertol. (Bartolucci et al. 2020), Bolboschoenus planiculmis (F.Schmidt) T.V.Egorova (Bartolucci et al. 2024a), Tilia americana L., and Sequoia sempervirens (D.Don) Endl. (original data).

Moreover, 44 taxa, either new or recorded for the province of Florence before 1950, were documented. Of these, 23 have been published by the author in previous floristic contributions, while 21 are presented as new findings within this study.

Based on field research, it is proposed to change the alien status in Tuscany of the nothospecies Populus × canadensis Moench nothosubsp. canadensis. This alien is widespread along the terminal stretch of the Sieve River, where it actively competes with the native Populus nigra L. subsp. nigra. The invasive potential of this alien in riparian environments has been repeatedly observed in other Italian rivers, such as along the Tiber and its tributaries in Lazio, and along the Tirso River in Sardinia (Galasso et al. 2021). On this basis, P. × canadensis in Tuscany should currently be considered a naturalized alien.

Other rare species in Tuscany are: Allium pallens L., Bellevalia webbiana Parl., Dactylorhiza insularis (Sommier) Landwehr, Dracunculus vulgaris Schott., Goodyera repens (L.) R.Br., Hordeum bulbosum L., Isolepis setacea (L.) R.Br., Linaria simplex (Willd.) Desf., Nymphaea alba L., Ophrys insectifera L., Sporobolus schoenoides (L.) P.M.Peterson, Spirodela polyrhiza (L.) Schleid., Taraxacum olivaceum Soest, Tulipa sylvestris L. and Zannichellia palustris L.

The discovery of new populations of B. webbiana, a narrowly Italian endemic species, is significant (Astuti et al. 2018a, 2018b; Peruzzi et al. 2020b, Peruzzi et al. 2022). According to Peruzzi and Carta (2011), the Area of Occupancy (AOO) of B. webbiana is currently very limited (68 km²) and is gradually decreasing (Gestri et al. 2010). These new sites notably expand the known range of this Italian endemic species.

The taxa showing some conservation interests (Rossi et al. 2013, 2020) are 17, 14 of which are categorized as Least Concern, two Data Deficient, two Near Threatened (Dactylorhiza insularis and Zannichellia palustris), one Vulnerable (Dracunculus vulgaris), and one Endangered (Bellevalia webbiana) at national level. Additionally, 10 species are included in the Regional Red Lists (Conti 1997), 83 are listed in the annexes of Regional Law No. 56/2000, and 8 are recorded in the “Repertorio Naturalistico Toscano” (Sposimo and Castelli 2005) (for more details, see Suppl. material 1).

Life forms and chorotypes show marked Eurosiberian affinities in agreement with the temperate and continental climate. Comparing the flora of the lower Sieve Valley with those of surrounding areas, the Sambre river valley (Selvi et al. 2016) and Cintoia valley (Ferroni et al. 2004) show similar proportions of hemicryptophytes, therophytes and geophytes compared to the lower Sieve Valley. The prevalence of hemicryptophytes and, at the same time, a high proportion of annual herbaceous plants, is likely due to the presence of open areas and the climate characterized by marked summer aridity. Similarly, the chorology indicates a codominance of Eurosiberian and transitional Eurosiberian-Mediterranean elements with a significant contribution from Mediterranean entities representing a transitional flora with a marked temperate and continental characters and the penetration of elements of Mediterranean origin.

The lack of confirmation for 30 old records, mainly located in the Monte Giovi area (see Suppl. material 1), could be the result of two concurrent factors: on one hand, the approximate information about the locality of data may have led to the inclusion of taxa occurring outside the study area (the northern slope of the relief belongs to the upper Sieve Valley); on the other hand, the increased forest cover due to the abandonment of agricultural land, coupled with extensive reforestation at the summit of Monte Giovi (Piussi 1962), may have resulted in a reduction of habitats suitable for these species.

The environments within the study area that host the most significant species are olive groves (Bellevalia webbiana, Dracunculus vulgaris, Tulipa sylvestris), fallow grasslands on soils of different water content (Allium pallens, Linaria simplex, Sporobolus schoenoides, Taraxacum olivaceum), riparian areas (Zannichellia palustris, Z. peltata, Bolboschoenus planiculmis, Leucojum vernum), and artificial water basins (Isolepis setacea, Nymphaea alba, Ranunculus trichophyllus Chaix, Zannichellia palustris). Conversely, the environments hosting the highest number of alien species are urban and riparian areas.

The most impacted habitats within the territory are water bodies (rivers, artificial basins) due to anthropogenic disturbances (hydro-morphological alterations, water over-exploitation, water pollution) and the invasion of alien species. Indeed, aliens are generally favored by disturbed and unstable environmental conditions (Lazzaro et al. 2020; Dimitrakopoulos et al. 2022). These data highlight both the significance and fragility of wetlands and artificial waterbodies for the conservation of rare hygrophilous taxa (Chester 2013), as already observed for other areas in Tuscany (Bonari et al. 2021). Notably, about 50% of Italy’s critically endangered species are hydrophytes (Rossi et al. 2013, 2020).

Finally, the widespread presence of aliens along the road network of the lower Sieve Valley and the recent arrival of the alien macrophyte Ludwigia peploides subsp. montevidensis, poses a serious threat to the integrity of the valley’s natural ecosystems. This is particularly relevant for the aquatic habitats, where L. peploides demonstrates a remarkable competitive ability with the native communities (Dandelot et al. 2008).

Marco D’Antraccoli (Botanic Garden and Museum, University of Pisa) is gratefully acknowledged for having calculated the SAR predictions. The financial support by Fondazione per la Flora Italiana for the publication fee is also gratefully acknowledged.