Azolla Lam.
Floating aquatic ferns with short stems bearing long roots. Lvs monomorphic, c. 0.5-2 mm long, imbricate, lacking veins, 2-lobed; upper lobe green and usually papillate; lower lobe hyaline. Mega- and microsporangia borne separately in stalked sporocarps on the lower lobes of the lvs. Spores trilete.
Key
1
Roots bearing lateral rootlets; plants regularly 2-pinnately branched, the secondary branchlets decreasing markedly in length toward proximal end of primary branches
Roots entire; plants irregularly branched, the secondary branchlets not decreasing in length towards proximal end of primary branches
6 spp., widespread, especially N. and S. America. Native sp. 1, naturalised 1.
Azolla spp. are free-floating and capable of covering large areas of slow-moving or still water. They are easily recognised as a red carpet of growth on the water surface. Fertile plants are rarely found and reproduction is usually vegetative.
