I discovered today that there is an online version of the Flora of Japan. Unfortunately it does not include any bryophytes, so no mosses, hornworts, or liverworts. The website allows you search for your favorite vascular plants in Japan by family, genus, or specific epithet. Some of the interesting features are that is gives you the common name of the plant in Japanese, both in romanji (roman letters that allow you to sound out the word) and in katakana (japanese characters used for spelling out typically foreign words). It also lists the other things you might expect from a flora: a brief description of the plant and habitat, the distribution in Japan and other countries, as well as the reference to the initial description of the species.
I looked up the listing for Isoetes, the fern relatives (Lycophytes) that I studied when I was an undergraduate student. They have four species in Japan. One of them is even named in honor of Japan, Isoetes japonica, which would make the common name in English the japanese quillwort (quill - referring to the fact that the leaves are hollow and slender like the quill of a feather and wort - an Old English word for plant). Its common name in Japanese is Mizu-nira, which translates to water-scallion. Both of these common names quillwort and water-scallion are really great descriptions for Isoetes.
If you have never seen an Isoetes, I have included a couple of photos that I had saved on my computer. This is Isoetes riparia (shore quillwort) and I found it growing around the edge of the Mansfield Hollow Dam, which is just down the road from the University of Connecticut. When the water level in the dam is high this plant would be submerged in up to six inches of water. This is fine by the quillwort. It doesn't mind being wet. Isoetes are typically aquatic or shore-edge plants and are found worldwide.
I can hardly believe that there was a time long ago in a state far away when I studied ferns and did not have any particular interest in mosses. (Well ok, it was only six years ago in Ohio.) Though they are not mosses, Isoetes are really great plants and were super fun to study!