Aquatic Floristic Surveys Reveal Overlooked Alien Macrophytes in Rice Fields of Northern Italy: Najas chinensis (Hydrocharitaceae) and Chara fibrosa s.l. (Characeae)

The alien flora of rice fields and associated aquatic habitats remains poorly documented. Surveys conducted in 2024–2025 in eastern Piedmont (Northern Italy) recorded several alien macrophytes. Here, we focus on two taxa: Najas chinensis N. Z. Wang (Magnoliophyta, Hydrocharitaceae) and Chara fibrosa C. Agardh ex Bruzelius s.l. (Charophyta, Characeae). In Italy, N. chinensis had previously been known from a single herbarium specimen collected in 2004 and recognised only years later through molecular analyses. We found it at more than half of the surveyed sites, suggesting that its apparent rarity may reflect limited floristic exploration rather than a genuinely restricted distribution. We also provide an identification key to the Italian species of Najas. C. fibrosa, a tropical–subtropical species historically associated with European rice fields and only sporadically recorded in Italy since the nineteenth century, is reported here for the first time from Piedmont, confirming its occurrence in the western Po Plain. Our findings show that even limited floristic surveys can reveal overlooked alien aquatic plants and improve knowledge of their distribution, thus highlighting the need to strengthen field monitoring activities.