As far as being "organized" you have a great variety of macros that look very similar to FW plants. Caulerpas have a rhizome and resemble ferns, mosses look a lot like algae and some genus share FW, brackish and SW habitats. Calcium algaes are much stiffer and more defined then most FW plants. Of course you also have dozens of flowering SW plants to choose from, seagrasses that resemble vals and sag, manatee grass that looks like hairgrass, and stargrasses that look like foreground plants.
I find it interesting that people on this site are so locked into the FW plants that they don't see that the marine plant hobby is about where planted tanks were in the 80's. Now that the FW plant tank has developed several clear methods to acheive success it seems that everything is just copied from someone else. In other words just spend the money and follow directions and you will have a beautiful planted tank.
The marine plant hobby might be that way 10-20 years into the future but it still is in the experimental stages now. That's why I find it interesting.
Anyway I'll get off my soapbox for now. Just like FW planted tanks, when done correctly, can be a thing of beauty so can SW planted tanks. SW plants offer a much bigger range of colors though.