Azolla pinnata subsp. asiatica
Vascular – Exotic
The National Vegetation Survey (NVS) Databank is a physical archive and electronic databank containing records of over 94,000 vegetation survey plots - including data from over 19,000 permanent plots. NVS maintains a standard set of species code abbreviations that correspond to standard scientific plant names from the Ngä Tipu o Aotearoa - New Zealand Plants database.
A small aquatic free floating perennial fern which forms a conspicuous red (green in shaded areas) mat on the water surface. Plants are 1-3 cm long, triangular in outline, and regularly branched. Leaves green to red. Roots densely covered with branched, fine, hair-like rootlets.
Abundant in the northern half of the North Island to the Rotorua Lakes with scattered sites further south to Levin.
Still and slow flowing water bodies in warm areas.
Wetland plant indicator status rating
OBL: Obligate Wetland
Almost always is a hydrophyte, rarely in uplands (non-wetlands).
Tiny free-floating aquatic fern, forming red-coloured mats (green in shaded areas). Plants 25 x 20 mm, triangular or 5-angled in outline, regularly branched. Leaves usually not overlapping, green turning red. Roots to 5 cm long; with fine, lateral rootlets.
Azolla rubra – a native floating fern. A. rubra is more ovate and irregularly branched. Rootlets are and unbranched. In comparison A. pinnata has regular 2 pinnate branching and its roots have fine rootlets.
This perenniel reproduces rapidly by fragmentation, forming dense mats across nutrient-rich still waters. Produces spores which may be spread by waterfowl.
Other dispersal mechanisms include downstream via waterflow and into new catchments via contaminated diggers, eel nets, boats and trailers, water fowl, occasionally by wind blown spores.
Tropical Africa, Asia, Australia
Reason for introduction
Possibly contaminant of ornamental pond plants, or a natural introduction from Australia being spread by migratory waterfowl.
Can be managed using floating booms that push floating plants to one end of a dam or small water body, then remove manually/mechanically. Only short-term control usually achieved.
Tolerates low to high nutrient water, high to moderate temperature. Intolerant of low temperatures and heavy shade. Does not dominate in moving water or expose surfaces.
azolla: From the Greek azo ‘to dry’ and ollo ‘to kill’, killed by dryness
pinnata: From the Latin pinna ‘feather’, in botany pinnatus ‘pinnate’ refers an arrangement of leaves, veins or branches in rows along a central axis, similar to the structure of a feather.
Factsheet prepared by Paul Champion and Deborah Hofstra (NIWA).
References and further reading
Champion et al (2012). Freshwater Pests of New Zealand. NIWA publication. http://www.niwa.co.nz/freshwater-and-estuaries/management-tools/identification-guides-and-fact-sheets/freshwater-pest-species.
Johnson PN, Brooke PA (1989). Wetland plants in New Zealand. DSIR Field Guide, DSIR Publishing, Wellington. 319pp.
Coffey BT, Clayton JS (1988). New Zealand water plants: a guide to plants found in New Zealand freshwaters. Ruakura Agricultural Cente. 65pp.
Popay et al (2010). An illustrated guide to common weeds of New Zealand, third edition. NZ Plant Protection Society Inc, 416pp.
Johnson, A. T., Smith, H. A. (1972). Plant Names Simplified: Their pronunciation, derivation and meaning. Landsman Bookshop Ltd: Buckenhill, UK.