Family: Iridaceae (iris)

Status: still promoted as garden plants despite their invasiveness.

Description:
Plants which grow from a bulb or corm are usually visible above ground for only part of the year. This is the case for most of the plants illustrated here, except for aristea which grows from a rhizome rather than a bulb, and has foliage visible all year round. Flowers are generally tubular in shape with petals flared at the rim. All have flat sword-like leaves with parallel veins. Watsonia has a raised mid-vein which is prominent on both leaf surfaces. Aristea has several prominent parallel veins and slightly bluish-green leaves and blue flowers.
Montbretia does not produce seed but spreads by underground runners. Watsonia meriana reproduces by aerial bulbils carried on the stems, and not by seed, unlike Watsonia borbonica, a more robust clumping plant without bulbils, distinguished by having pink flowers (those of W. meriana are orange or red). The others spread both from seed and from offset bulbs produced at the base of the parent bulb. Numerous seeds are carried in leathery or papery capsules.

Preferred habitat and impacts:
All appear mostly around towns and old farms and on nearby roadsides, as they are garden escapees. They can form a dense groundcover, excluding native species.

Dispersal:
Dumping of garden waste spreads both seeds and bulbs. Wind spread of seeds occurs in some, though not usually over long distances as the seed is relatively heavy. Slashing of roadside infestations while in seed can spread infestations, as can movement of contaminated soil.

Look-alikes:
There are some native members of the iris family which have leaves present all year round, and generally have smaller flowers than the garden plants. Examples are the purple flag (Patersonia species) which usually grow in poor sandy soils in heath and dry forest, and Libertia paniculata which has small white flowers and grows in shady gullies. Other native plants which grow from bulbs and are not visible for part of the year are the bulbine lilies (Bulbine glauca or B. semibarbata) which have onion-like leaves and tall spikes of yellow flowers. They are likely to grow around rock outcrops or in grassy remnant vegetation in the farming areas.

Other weedy members of the iris family are:

• homeria (Homeria flaccida and H. collina ), with yellow or salmon-pink flowers,
• onion grass (Romulea rosea ) with grass-like leaves and small pink flowers in short stems held very close to the ground,
• scour weed (Sisyrinchium iridifolium and Sisyrinchium species A) with white to cream flowers with a brownish-purple centre and purple central stripe on the petals,
• gladiolus (Gladiolus species), some of which occasionally naturalise around towns.

Control:
Small infestations can be dug out, but this should be done when soil is moist (though not too wet), to avoid leaving behind the bulbs, or the small bulbils which develop around the base of the parent bulb late in the season. As an interim measure, to prevent seed shed, cut tops after flowering, or if seed has already formed, cut and bag seed heads for safe disposal. Do not slash seeding plants, as it will spread the seed. Persistence will be needed with digging out, as regrowth is likely. Selective or non-selective herbicides can be used. The best time for spraying is when the flower stalks are elongating, as the bulbs will be most weakened at this time, and seeding and production of new bulbils should be prevented.