Azolla

Scientific name

Azolla Lam.

Common names

pond fern, mosquito fern, water velvet

Family

Azollaceae

Similar genera

not likely to be confused with any other plant genus

Native distribution

cosmopolitancosmopolitan:
(adj) essentially worldwide in distribution
in warmer regions of the world

Species cultivated

Azolla caroliniana Willd.

A. filiculoides Lam.

A. mexicana Schlecht. & Cham. ex K. Presl.

A. nilotica Mett.

A. pinnata R. Br.

U.S. Federal Noxious Weed: Azolla pinnata

Identification: Diagnostic characters: vegetativevegetative:
(adj) (1) pertaining to or to the growth of plant organs or plant parts that have nonreproductive functions, such as leaves, roots, stems, etc.; (2) concering non sexual propagules such as tubers, turions, stem fragments, root crowns, rhizomes
: triangular shape of plants, feathery appearance of roots; sexual: megasporangium has 9 floats; microsporangial massulaemassula:
(n) (pl. massulae) in Azolla, a mucilaginous group of microspores within the microsporangium
have no glochidiaglochidium:
(n) (pl. glochidia) a hair-like process bearing an anchor-like tip, that projects from the surface of microsporangial massulae in the Salviniaceae
, but have vacuolatedvacuolated:
(adj) having a vacuole or vacuoles
trichomes.

See Azolla pinnata disseminule fact sheet.

Adventive distribution

some species are nearly cosmopolitancosmopolitan:
(adj) essentially worldwide in distribution

Weed status

Azolla pinnata is considered one of the world’s most troublesome weeds and it is an aquatic weed on the U.S. federal noxious weed list.

Habit

small, free-floating, with tiny, crowded, bilobed leaves

Brief description

Annual or perennialperennial:
(adj) (of a plant) having a life cycle of more than two years
water fern. Stem floating, more or less pinnately branched. Roots simple, with root hairs present or absent at nodes. Leaves in two alternatealternate:
(adj) (of leaves) bearing one leaf per node; placed singly on the stem at different heights
rows, overlapping and covering stem, divided into two lobes; upper lobe aerial, thickened and photosynthetic (red or green colored), lower lobe submersedsubmersed:
see submerged
and non pigmented. A thin-walled pouch forms on the upper lobe, enclosing cavities containing nitrogen fixing cyanobacteria (Anabaena azollae Strasb.). Sporocarps borne in pairs in leaf axils of older branches; megasporocarps small, containing a single megasporemegaspore:
(n) in plants that produce two different kinds of spores, the larger of the two types, which develops into the female gametophyte
; microsporocarps with many microsporangiamicrosporangium:
(n) (pl. microsporangia) a saclike structure that produces microspores
. Dispersal by spores or stem fragments.

Natural habitat

still waters of all types of water bodies

Additional comments

The genus Azolla comprises seven species of small-leaved floating ferns, some of the cultivated species are currently taxonomically unresolved. Azolla species form a symbiotic relationship with the cyanobacteria Anabaena azollae, which fixes nitrogen and grows in a cavity in the dorsaldorsal:
(adj) (1) of the back of an organ or the side turned away from the axis (syn. abaxial) (compare ventral); (2) in thallose plants (e.g. liverworts); of the upper surface
lobe of the fern's leaves.