Onion grass

Romulea rosea (L.) Ecklon var. australis (Ewart) De Vos

Synonyms - Ixia rosea, Romulea bulbocodium, Romulea cruciata var. australis, Romulea longifolia, Romulea parviflora, Romulea rosea var. communis, Romulea rosea var. reflexa, Trichonema longifolium,

Family: - Iridaceae.


Romulea celebrates Romulus the founder of Rome.


Onion grass

Other names:

Guildford grass because heavy infestations occurred in the Guildford area in WA.


Onion Grass, locally known as Guildford Grass, is a small herb with long and slender, but very tough and wiry , cylindrical basal leaves which are produced annually from a pea-sized corm. The flowers are formed at the base of the plant on stalks that gradually elongate upwards during flowering and then recurve in fruit. The star-like flowers have a short broad yellowish tube and 6 pink to purple pointed petal lobes that are 8-15 mm long. There are 3 stamens and a slender 6-branched style.

It is a common weed of roadsides, gardens, crops, pastures and bushland. Onion Grass is native to South Africa and flowers in late winter and spring.




First Leaves:

Tightly rolled so as to appear cylindrical. Dark green. Shiny. Small, flat, white corm at base.


1-10 arise from the base and along a very short stem.

Blade - Dark, shiny, green, flattened cylindrical, slender, wiry, tough, 50-400 mm long by 0.5-2 mm wide, parallel veins, blunt edges, tip pointed. Hairless. 2 lengthwise grooves on each side so the cross section looks like a Maltese cross.

No auricles or ligule because it is not a true grass.


Very short covered by leaf bases.

Flower stem - Slender peduncle, 30-200 mm long.

Flower head:

2-4 flowers borne singly in the axils of 2 bracts on the ends of somewhat erect stalks(peduncles), 30-200 mm long and shorter than the leaves.


15-50 mm diameter with 6 pink 'petals' and a yellow cup and 8-15 mm wide throat (throat sometimes blue/violet), that is twice as long as the spathe. Flowers are short lived and close in dull weather and at night.

Spathe bracts - 2 of similar size attached to the base of the ovary, 8-12 mm long, papery, striped, persistent. Outer one with a brown papery tip. Inner one with broad, papery, brown dotted or streaked edges.

Ovary - Slender style, slightly shorter than the stamens with 3 deeply forked branches.

Perianth - Funnel shaped, tube 1.5-2 mm long with 6, spreading, symmetrically arranged, narrowly egg shaped segments, 8-25 mm long by 3-8 mm wide, with a yellow base. Segments, pink to purple (rarely white) on the inside with a yellow base and greenish pink on the outside with 3 darker veins on the back. Tend to dry to a deeper purple colour.

Stamens - 3, half as long as the perianth and slightly longer than the style. Alternate with the style branches. Filaments free, short

Anthers - Erect, yellow, 3-5 mm long, attached at the base.


Oblong, cylindrical, wrinkled, 6-12 mm long and shorter than the bracts, leathery capsule on 30-200 mm stalks that are initially curved and straighten as the fruit ripens. 3 celled with 4-12 seeds in each cell. Breaks open from the top to release the seed when ripe.


Globular, slightly flattened, reddish- brown.


Fibrous from the bottom of the corm.

Corm, egg shaped to spherical, 5-20 mm wide, encased in a glossy, brown, dry scales.

Special contractile roots pull the corm deeper into the soil each year.

Key Characters:

Flowers pink or purple with a yellow cup, 15-20 mm long overall with a 1.5-3 mm tube.

Spathe half as long as the flowers.

From J.M. Black and T.D. Macfarlane.


Life cycle:

Annual shoots with perennial rootstock. Germinates or sprouts in autumn to winter, grows over winter and flowers from August to November. The flowers initially open close to the ground then the stalks elongate to lift them into the air and then bend downward to take the maturing capsule back to ground level. Contractile roots form in spring and pull the corm deeper into the soil as it dries out. Top growth dies in summer leaving a perennial corm in the soil.



By seed and perennial rootstock.

Flowering times:

Spring in western NSW.

August to November in SA.

August to October in Perth.

Seed Biology and Germination:

Vegetative Propagules:

Underground corm.



There are 2 varieties in WA. var. communis has larger magenta flowers and var. australis has smaller, paler pink flowers.


Population Dynamics and Dispersal:

Spread by seed.

Pigs dig up and eat the corms.

Origin and History:

South Africa.





Temperate. Mediterranean.

More abundant in the higher rainfall areas.


Wide range including limestone and granitic derived soils and clays.

More abundant on relatively bare or compacted soils.

Plant Associations:



Low value fodder.


A weed of crops, pastures, grass lands, roadsides, open woodland, lawns, gardens, limestone heaths, granite outcrops, clay wetlands and disturbed areas.

Causes yield reductions due to competition.



May cause fibre balls in the stomachs and bowels of cattle, horses and sheep.

Suspected of causing infertility, abortion and paralysis or romulosis in sheep and may be caused by a leaf spot fungus (Helminthosporium biseptatum) associated with Onion Grass.


Fibre balls may cause chronic scouring in cattle.


Laxatives are of little use. Surgery is occasionally used.

Feed hay or alternative fibre when pasture is lush in infested paddocks or remove stock when they start to eat quantities of Onion Grass.



Management and Control:

Summer cultivation to expose and desiccate corms provides some control. Chlorsulfuron, metsulfuron, glyphosate, imazapyr and imazethapyr provide reasonable control in various cropping situations. In pastures, late applications of glyphosate provides some suppression and imazethapyr can provide control in legume pastures. Deep rip soil if compacted.

In lawns metsulfuron provides good control or mowing with a rotary mower every 2 weeks for a few years will eventually exhaust the corm.

In cropping areas, spray with glyphosate, cultivate, then plant a cereal and treat with chlorsulfuron.


Eradication strategies:

Manual control is difficult because the leaves tend to break off, leaving the corm buried, unless the soil is loose. Very regular and close mowing with a rotary mower to exhaust corms, or cultivation in summer or early autumn to expose corms so they dry out and die, provides some control but may also spread the infestation.

Spray with 0.5 g chlorsulfuron(750g/kg) plus 25 mL Pulse® in 10 L water in winter before flowering. Larger areas can be sprayed with 20 g/ha chlorsulfuron(750g/kg) plus 0.25% Pulse®. 20 g/ha metsulfuron(600g/kg) plus Pulse® or 2 L/ha paraquat(250g/L) plus Pulse® also provides reasonable control in winter before flowering.

Blanket wiper treatments using 1-2 L/ha of glyphosate(450g/L) in combination with 10-20 g/ha of chlorsulfuron or metsulfuron have also worked well.

50 g/ha Raptor® plus 0.25% Pulse® has provided good control in trials and may be less damaging to bush. Use 1 g Raptor® plus 2.5 mL Pulse® in 10 L water for hand spraying.

Repeat treatments for at least 2-3 years.

Deep rip soil if compacted. Plant vigorous perennial species.

Herbicide resistance:

Biological Control:

Related plants:

Small-flowered Onion Grass (Romulea minutiflora) has small flowers with 'petals' up to 9 mm long with rounded tips.

Romulea flava has yellow flowers.

Romulea obscura has orange flowers.

Plants of similar appearance:

Thread Iris, Cape Tulip, Annual Ryegrass, Barley grass, Brome grass, Darnel, Fountain grass, Quaking grass, Sand fescue, Silver grass, Volunteer Cereals, Wild Oats, Toad Rush, Winter grass.


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