yellow flag iris
Vascular – Exotic
Herbs - Monocots
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.
Dense leafy clumps with dark to yellow green foliage up to 1.5 m tall with purple coloration at the base of each fan-shaped group of leaves. Showy yellow iris flowers (12 cm across) produced in early spring, only lasting one day and when ripe forming large green capsule (2 x 5 cm long)
Widely naturalised, it is scattered throughout both main islands being locally abundant in the Waikato and the margins of the Avon River in Christchurch.
Still and slow flowing water bodies, wetlands and reported from salt marshes overseas.
Wetland plant indicator status rating
OBL: Obligate Wetland
Almost always is a hydrophyte, rarely in uplands (non-wetlands).
Tall marginal summer-green perennial. Dark green, leafy clumps. Leaves sword-shaped, 2-3 cm wide that shred to fibres when old. Stems round with several long leaves; leaves emerging in fans from reddish base. All parts odourless when crushed. Rhizomes up to 3 cm diameter. The flower stalk is stout, flowers are yellow (occasionally pale cream) and up to 12 cm across. The capsule is up to 5 cm long with brown flattened disc like seeds. Plants growing over water can form rafts of floating rhizomes, strong enough to support the weight of a human.
Raupo (Typha orientalis) has a narrower leaf than yellow flag and has a characteristic twist in the top of the leaf blade. Manchurian wild rice (Zizania latifolia) is much taller and has sharp-edged leaves.
September to December
December to March
Perennial. Reproduces by rhizomes and seed, there are many viable seeds contained in each capsule.
Seeds and rhizome fragments spread by water and contaminated machinery, and deliberate planting.
Europe, northern Africa and western Asia.
Reason for introduction
Ornamental pond plant
Can be controlled manually, mechanically or herbicidally depending on situation.
Tolerant of saline, frost, flooding and drought, high-low fertility, physical damage and many soil types.
iris: From the Greek iris ‘rainbow’, presumably in reference to the many colours of the flowers (Johnson and Smith, 1986).
National Pest Plant Accord species
This plant is listed in the 2020 National Pest Plant Accord. The National Pest Plant Accord (NPPA) is an agreement to prevent the sale and/or distribution of specified pest plants where either formal or casual horticultural trade is the most significant way of spreading the plant in New Zealand. For up to date information and an electronic copy of the 2020 Pest Plant Accord manual (including plant information and images) visit the MPI website.
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.
Johnson, A. T. and Smith, H. A (1986). Plant Names Simplified: Their pronunciation, derivation and meaning. Landsman Bookshop Ltd: Buckenhill, UK.
Popay et al (2010). An illustrated guide to common weeds of New Zealand. NZ Plant Protection Society Inc, 416pp.
Sculthrope CD (1967). The biology of aquatic vascular plants. Edward Arnold Publishers, London. 160pp.