Azolla Lam.

2 species native AUST.; all states and territories

Aquatic ferns, often forming a carpet on the surface of slow-moving or stagnant water. Plants ovate or triangular, usually 0.8–6 cm long, 0.8–4 cm broad. Leaves in 2 rows, very numerous, up to 1.5 mm long, imbricate, often papillose, unequally 2-lobed; the upper lobe with a colony of the cyanobacteria Anabaena in the central cavity; the lower lobe thin, submerged, bearing in the axils 2–4 megasporocarps or microsporocarps or sometimes a sorus of each type. Microsporocarps ovoid or globular, up to 2 mm long, protected by a membrane-like indusium which encloses a cluster of 7–100 orbicular-headed microsporangia, each of which is borne on a long narrow pedicel. Microsporangia containing 4–10 massulae which bear few to many glochidiate or non-glochidiate, septate or non-septate processes on one or all sides. Microspores 32–64, occurring in groups within the massulae. Megasporocarps oblong, with a conical apex, protected by a membrane-like indusium. Megaspores solitary in the megasporocarps, consisting of a rounded basal portion which is smooth or pitted or with raised hexagonal markings, surmounted by 3 or 9 floats.