The hairy four-leaved water clover is a species with a strictly Mediterranean, mainly western distribution which is present, but generally very rare, near Taranto in Puglia, in Basilicata, and in Sardinia. It grows in marshes and along the edge of ponds, from sea level to about 500 m. Of the 19 known Italian stations for this species, which is considered vulnerable on a national scale, 17 are located in Sardinia, mainly along the banks of the Coghinas Reservoire (Bagella & Caria, 2012) in the municipalities of Oschiri, Ozieri and Tula (OT) (Calvia & Urbani, 2007; Caria et al., 2014). The other stations are located in the Provinces of Nuoro near Dorgali (Peroni & Peroni, 2002) and Oliena, in the Province of Cagliari near Teulada and Orroli, and in the Province of Medio Campidano near Gesturi (Caria et al., 2013). The species is listed in Annexes II and IV of the Habitats Directive and Annex I of the Bern Convention, falling into the vulnerable category (Caria et al., 2013). The genus is dedicated to Luigi Ferdinando Marsili (1658-1730), founder of the Institute of Botanical Sciences of Bologna; the species name in Latin means 'skinny, thin'. Sporulation period: March to June.

Italian name(s): Marsilea strigosa (Italia), Quadrifoglio acquatico strigoso (Italia).