2 adjectives to describe cryptogamia

The next day, instead of the sea-serpent, he finds on the beach an immense cryptogamia, a gigantic alga, of a single piece, divided into a thousand cylindrical branches, and much superior to all those he has observed in the Straits of Sunda.

[Footnote 1: It is the Durvilloea utilis, dedicated to Dumont d'Urville, by Bory de St. Vincent, and classed by him in the laminariées, an important and valuable family of marine cryptogamia.

2 adjectives to describe  cryptogamia