[1] Salviniales are all aquatic and differ from all other ferns in being heterosporous, meaning that they produce two different types of spore (megaspores and microspores) that develop into two different types of gametophyte (female and male gametophytes, respectively), and in that their gametophytes are endosporic, meaning that they never grow outside the spore wall and cannot become larger than the spores that produced them.

[1] In being heterosporus with endosporic gametophytes they are more similar to seed plants than to other ferns.

Aerenchyma is frequently present in roots, shoots, and petioles (leaf stalks).

In the molecular phylogenetic classification of Smith et al. (2006), the Salviniales were placed in the leptosporangiate ferns, class Polypodiopsida.

[1] The linear sequence of Christenhusz et al. (2011), intended for compatibility with the classification of Chase and Reveal (2009)[3] which placed all land plants in Equisetopsida,[4] reclassified Smith's Polypodiopsida as subclass Polypodiidae and placed the Salviniales there.