Iris pseudacorus
NPPA pest plant
Environmental Weed (2024)
Common names
yellow flag iris
Biostatus
Exotic
Category
Vascular
Structural class
Herbs - Monocots
Simplified description
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)
Flower colours
Orange, Yellow
Detailed description
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.
Similar taxa
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.
Distribution
Widely naturalised, it is scattered throughout both main islands being locally abundant in the Waikato and the margins of the Avon River in Christchurch.
Habitat
Still and slow flowing water bodies, wetlands and reported from salt marshes overseas.
Conservation status
Not applicable
Detailed taxonomy
Family
Ecology
Flowering
September to December
Fruiting
December to March
Year naturalised
1978
Origin
Europe, northern Africa and western Asia.
Reason for introduction
Ornamental pond plant
Tolerances
Tolerant of saline, frost, flooding and drought, high-low fertility, physical damage and many soil types.
Control techniques
Can be controlled manually, mechanically or herbicidally depending on situation.
Life cycle and dispersal
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.
Wetland plant indicator status rating
Information derived from the revised national wetland plant list prepared to assist councils in delineating and monitoring wetlands (Clarkson et al., 2021 Manaaki Whenua – Landcare Research Contract Report LC3975 for Hawke’s Bay Regional Council). The national plant list categorises plants by the extent to which they are found in wetlands and not ‘drylands’. The indicator status ratings are OBL (obligate wetland), FACW (facultative wetland), FAC (facultative), FACU (facultative upland), and UPL (obligate upland). If you have suggestions for the Wetland Indicator Status Rating, please contact: [Enable JavaScript to view protected content]
OBL: Obligate Wetland
Almost always is a hydrophyte, rarely in uplands (non-wetlands).
Other information
Etymology
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.
Environmental Weed (2024)
This plant is named in a list of 386 environmental weeds in New Zealand 2024 prepared by DOC. 759 candidate species were considered for inclusion on this new comprehensive list of environmental weeds in New Zealand. The species considered were drawn from published lists of weed species, lists of plants that must be reported or managed by law if observed, existing national and regional programmes and agreements for pest management, and species already managed by the Department of Conservation (DOC). Candidate species were then assessed to see if they were fully naturalised and whether they have more than minor impacts in natural ecosystems. Read the full report here.
NVS code
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.
IRIPSE
Referencing and citations
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.
Attribution
Factsheet prepared by Paul Champion and Deborah Hofstra (NIWA).