Species

Iris pseudacorus

Etymology

Iris: From the Greek iris 'rainbow', presumably in reference to the many colours of the flowers (Johnson and Smith, 1986).

Common Name(s)

yellow flag iris

Authority

Iris pseudacorus L.

Family

Iridaceae

Brief 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)

Flora Category

Vascular - Exotic

NVS Species Code

IRIPSE

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.

Structural Class

Monocotyledonous Herbs

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.

Features

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.

Flowering

September to December

Flower Colours

Orange,Yellow

Fruiting

December to March

Year Naturalised

1978

Origin

Europe, northern Africa and western Asia.

Reason for Introduction

Ornamental pond plant

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.

Tolerances

Tolerant of saline, frost, flooding and drought, high-low fertility, physical damage and many soil types.

Attribution

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.  

This page last updated on 5 Jun 2014