Azolla pinnata

Salviniaceae

Azolla pinnata R.Br.

Link to Australian Plant Name Index for publication details and synonyms: https://id.biodiversity.org.au/name/apni/115380

Free-floating, aquatic ferns. Stem short, creeping, bearing short roots and sometimes trichomes. Leaves small, imbricate, fleshy; margins transparent, bilobed; upper lobe 1–2 mm long, usually minutely to strongly papillate, lacking veins, containing the cyanobacterium Anabaena azollae in central cavity; lower lobe submerged and bearing 2–4 megasporangia or microsporangia in axils. Megasporocarps oblong-conical, protected by a membrane-like indusium; megaspores solitary; basal portion rounded, smooth, pitted or with raised, hexagonal markings surmounted by 3–9 floats. Microsporocarps ovoid to globular, covered by a transparent indusium; microsporangia 7–100, spherical, stalked, containing 4–10 massulae bearing few to many, hooked or non-hooked, septate or non-septate processes. Microspores 32–64, in groups within massulae. 

Plants triangular in outline, branching regularly, pinnate; roots feathery. Leaves oblong-triangular; apex rounded; margins slightly membranous; surface prominently tuberculate in basal half, dull reddish brown or green. Microsporangiate massulae ±conical, with 1–6 non-barbed processes aggregated at one end. Megasporocarps brown, partially obscured by leaf lobes. Megasporangia each with 9 apical, swimming floats. 

Widely scattered across Australia including man-made habitats. Also widespread outside Australia.

Free-floating aquatic fern occurring on still or slow moving water, particularly man-made dams and ponds.

Plants irregularly branched, roots simple = Azolla rubra

Plants regularly branched, roots feathery = Azolla pinnata