Azolla

Stems are very short and slender, easily broken, green. Leaves are a few millimeters in size, alternate, in 2 rows along upper side of stem, usually overlapping, divided into dorsal (floating) lobe and ventral (submersed) lobe; dorsal lobe oblong or ovate, densely papillose adaxially, fleshy, with a cavity near base containing blue-green algae (Anabaena), green, yellow, or red; ventral lobes hell-like, transparent, colorless, or reddish and slightly thickened near base. Sporocarps (spore producing structures) are usually in pairs (or 4 together), at base of lateral branches. Heterosporous with separate mega- and microsporocarps that produce megaspores and microspores, respectively. The gametophytes are endosporic (retained within the spore). Roots are submerged, either solitary or in clusters,growing from stem branching points; with numerous root hairs.