How small can aquatic ferns be?

Aquatic ferns can be quite small, with the mosquito fern (genus Azolla) being a notable example. These plants are typically very small, often measuring less than 2.5 cm (1 inch) in length.1

While the world's smallest terrestrial fern is the Indian species Ophioglossum malviae, which reaches an average size of only 1–1.2 cm (0.39–0.47 inch), the Azolla genus represents a group of aquatic ferns that are similarly diminutive in their physical scale.21