Potamon fluviatile and covers parts of many countries with a Mediterranean coastline. It is found in mainland Italy and on the Balkan Peninsula from Dalmatia to the Axios River in Greece. It is also found on a number of islands, including Sicily, Malta and Gozo, the Ionian Islands, Aegean Islands, Sporades and Andros in the Cyclades. Although the species as a whole is widespread, it is declining in numbers, and these insular populations are particularly vulnerable. "Potamon fluviatile" is widely distributed in much of mainland Italy, especially in the provinces of Trento, Lombardy, Veneto, Liguria, Tuscany, Umbria, Lazio, Campania, Apulia, and Calabria,
Blechnum fluviatile a short trunk central to a surrounding colony. The hardy "B. fluviatile" requires moist, shaded conditions for optimal growth. A small ground fern, the "B. fluviatile" is native to New Zealand and southeast Australia, a syntype common throughout the country in damp, shady areas in acidic, moist and boggy soil, beside streams in forest areas. This fern species occurs throughout much of New Zealand's forests, including much of the forested area of North Island; west, north and south coasts of South Island; and Stewart Island/Rakiura; moreover, it occurs in parts of the coastal forests of southeast Australia. Example understory flora