Phil Bendle Collection:Azolla pinnata (Ferny azolla)

Kingdom: Plantae
Division: Pteridophyta
Class: Polypodiopsida/Pteridopsida
(disputed)
Order: Salviniales
Family: Salviniaceae
Genus: Azolla
Species: A. pinnata
Binomial name: Azolla pinnata
Synonym: Azolla pinnata subsp. asiatica
Common name: Ferny azolla, Mosquito fern, Feathered mosquito fern, Water velvet.

A tiny aquatic free-floating, fresh water, perennial fern that is native to much of Africa, Asia (Brunei Darussalam, China, India, Japan, Korea, and the Philippines) and parts of Australia. The small invasive fern that inhabits is still and slow flowing water bodies. In New Zealand, it is found in the northern half of the North Island to the Rotorua Lakes, with scattered sites further south to Levin.
It is an invasive pest because its dense mats reduce oxygen in the water. It also crowds out other plants such as the native fern Azolla rubra to which looks very similar.

Azolla pinnata forms a conspicuous red (green in shaded areas) mat on the water surface. It has a triangular frond measuring up to 2.5 centimetres in length, is regularly branched. The frond is made up of many rounded or angular overlapping leaves each 1 or 2 millimetres long. The leaves are green, blue-green, or dark red in colour and coated in tiny hairs, giving them a velvety appearance. These hairs make the top surface of the leaf water-repellent, keeping the plant afloat even after being pushed under. The leaves contain the cyanobacterium Anabaena azollae, which is a symbiont that fixes nitrogen from the atmosphere that the fern can use. This gives the fern the ability to grow in habitats that are low in nitrogen. The roots are densely covered with branched, fine, hair-like rootlets that are > 5 cm long.
Azolla pinnata reproduces vegetatively when branches break off the main axis, or sexually when sporocarps on the leaves release spores which are spread by waterfowl, boats, trailers and water movement. 

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Thanks to Wikipedia for text and information:

https://creativecommons.org/licenses/by-sa/3.0/ 

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