Hey, experts, I realize this is probably a long-shot, but -

[MaeAnn]

In an illustrated book from the 18th century, in the aquatic plants and animal section, I found one illustration that unlike the rest, has a number but no name specified at the bottom of the page. Again, it's an illustration about 250 years old, maybe it's long extinct, but I thought i'd try.
Thanx!

[acabgd]

I highly doubt this is a marine plant and would therefore suggest you are in a wrong forum.