The term bulb refers to specialized leaf bases that serve as a storage structure and are specifically located above the true root structure. To my knowledge, bulbs are a monocot exclusive. Tubers on the other hand get around Like Robert said, Nephrolepis cordifolia produces tubers on its roots but as far as I know they will not propagate if separated from the plant and are primary water storage which attests to this fern's high dry tolerance (for a fern). It spreads by stolons. I can't think of any others at the moment but they are probably out there. Fleshy rhizomes tend to be more common in ferns. Cystopteris bulbifera & Asplenium bulbiferum produce adventitious shoots that develop an admittedly tuber-like ball of rhizome that would be specialized stem that in turn produces the true roots and leaves. It is technically not a tuber but rhizome. Woodwardia orientalis is another fern that does this. Alani Davis