Phenotypic plasticity of Platanus acerifolia (Platanaceae): morphological and anatomical trait variations in response to different pollution levels in Rome

Platanus acerifolia (Aiton) Willd (syn. Platanus × hispanica Mill. ex Münchh.) was generated spontaneously around the beginning of the 1600s in Spain between Platanus orientalis L. native to South-Eastern EuropeAsia Minor, and Platanus occidentalis L. native to North America. P. acerifolia has wide adaptability to various types of soils even those strongly alkaline (Pignatti, 1982) and it is particularly resistant to stress factors, including pollution (Pourkhabbaz et al., 2010 Gratani & Varone, 2007). It can adapt even at low temperatures and has a higher growth rate than its ancestors (Cennamo & Cafasso, 2002). For these characteristics, starting from the middle of the 1600s, P. acerifolia was imported in England and widely used in gardens, along with irrigation canals and roadsides with the name of the “London plane” (Cennamo & Cafasso, 2002) and then widely distributed throughout Europe. In Italy, this species has been largely used to adorn squares and avenues (Pignatti, 2017) since the beginning of the 20th century (Gratani & Varone 2007). P. acerifolia has high longevity (about 500 years) and it can reach 40 m in height. The stem has a monopodial growth, tapered in the apical part, main branches mighty, more or less twisted, with an angle of insertion to the stem of 45°. The crown has an expanded globular-oval shape.