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Azolla pinnata
Lee Kong Chian Natural History Museum

Azolla pinnata R. Br., 1810

Kingdom:Plantae
Phylum/Division:Filicophyta
Class:Pteridopsida
Order:Polypodiales
Family:Salviniaceae
Genus:Azolla
Species:A. pinnata
Common Names:Mosquito Fern
Status:Exotic, naturalised

Description

This is a small aquatic fern with a branched rhizome bearing solitary roots that are 1-5 cm long. The fronds are in two rows, triangular- to trapezoidal-shaped, 2-4 x 1 cm and bilobed. The dorsal lobe is above the water while the ventral lobe floats on the water. The lower lobe contains the blue-green alga, Anabaena azollae which is normally green but turns red under adverse environmental conditions. The sporocarps are in pairs or fours at the base of branches, each containing a megasporangium or 64 microspores.

Read more about the Polypodiales order.
Read more about the Salviniaceae family.

Distribution

Origin unknown. Found throughout tropical Asia, in southern and eastern China, southern Japan, northern Australia and tropical and southern Africa.

Localities

Sungei Buloh Nature Park

Locality Map

General Biology

The freshwater fern fragments easily, each piece growing to form a separate plant. This helps it spread rapidly, to cover the surface of the water, thus it can be a troublesome weed.

Life Cycle

For an account of the life history of a fern, see Pyrrosia piloselloides. Unlike most ferns, this water fern produces microspores and megaspores. The former are not released directly into the water but as clusters held together by  hardened mucilage, the massula. These massulae bear trichomes that allow them to stick to the hairs of the megasporangia. When the megaspores are released and develop into prothalli that in turn bear archegonia, the microspores germinate and release antherozoids that find their way into the archegonia to fertilise the eggs.

Human Uses

Azolla is in a symbiotic association with the blue-green alga, Anabaena azollae that has the ability to fix atmospheric nitrogen. As such, it has been used as a green fertiliser, especially in rice production in Southeast Asia. The plant has also been commercially used to produce compost. It has also been  used as a fodder for pigs, chickens, ducks, fish and even rabbits. A dense covering can control mosquito breeding, thus the common name. In the Philippines the plant is incorporated in various dishes like omelette, salads, pinangat and mungo.

References

de Winter, W. P. & V. B. Amoroso (eds.), 2003. Plant resources of South-East Asia No. 15(2). Cryptogams: Ferns and fern allies. Prosea Foundation, Borgor, Indonesia. 268 pp.

Holttum, R. E., 1966. A revised flora of Malaya. II Ferns of Malaya. Govt. Printing Office, Singapore (2nd ed.). 653 pp.

Parris, B. S., R. Khew, R. C. K. Chung, L. G. Saw & E. Soepadmo (eds.), 2010. Flora of Peninsular Malaysia. Series I: Ferns and Lycophytes. Vol. 1. Malayan Forest records No. 48. Forest Research Institute of Malaysia, Kepong. 249 pp.

Wee, Y. C., 2005. Ferns of the tropics. Times Editions-Marshall Cavendish, Singapore. 2nd ed. 190 pp.

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