Spinyhead Sida

Sida acuta Burman f.

Family: - Malvaceae.


Sida is from the Greek side and was used to refer to an unknown plant.

Acuta is from the Latin acutus and means 'sharp' or 'pointed' referring to the spiny nature of the head.

Spinyhead Sida refers to the sharp awns on the flower head and its membership of the Sida genus.

Other names:

Broomweed (Fiji, Jamaica)

Cheeseweed (Brazil)

Southern Sida (USA)

Taaiman (South Africa).


A fibrous stemmed, sparsely branched shrub to 1.5 metres tall with slightly concave, spiny tooth edged leaves and yellow, 1-2 cm wide flowers from February to September with two pronged seeds. It has annual tops with a perennial rootstock.






Stipules - 2 of different lengths.

Petiole - Short, hairy.

Blade - Narrow lance shaped, 20-90 mm long by 5-40 mm wide. Sides toothed. Base squarish. Prominent veins underneath. Hairless or with sparse star type hairs.


300-1500 mm high, slender, erect or spreading, fibrous to woody, branching from the base. Tough stringy bark.

Flower head:

Single or occasionally many crowded together in leaf axils.


Yellow, 10-20 mm wide. Slender, bent stalk.

Ovary -

Calyx - Pale green, 5 lobes. Lobes 6 mm long.

Petals - 5, joined at the base, 3-10 mm long. Tip shallowly notched.

Stamens -

Anthers -


Dark brown, rough, hard capsule, 3-5 mm diameter. Breaks into 5-8 segments.


Red-brown to black, wedge shaped, deeply indented on both sides 1.5-2 mm long. Rounded on the back. Tapers into 2 sharp beaks.


Stout, branching taproot, 600-1000 mm deep.

Key Characters:


Life cycle:

Perennial. Seed germinates mainly within the first two months of the growing season. Seedlings establish quickly, flower in mid to late summer and set seed in autumn. Flowers open in the morning and wilt in the afternoon. Stems and leaves usually die during the dry winter. New growth shoots from the rootstock when the wet season starts. In areas with no dry season it will flower all year.



By seed and perennial rootstock.

Flowering times:

Most of the year in areas with no distinct dry season.

February and September in WA.

Seed Biology and Germination:

Most is dormant when shed.

Impermeable seed coat prevents germination for some years. About 30% of the seed produced in one year is carried into the next year.

Scarification and acid treatment improve the germination percentage.

High alternating temperatures required for germination.

Seedling sensitive to shade and competition.

Vegetative Propagules:

Crown and perennial rootstock.


Sub species carpinifolia occurs in WA.


Population Dynamics and Dispersal:

It produces large quantities of seed.

Spread by seed with spiny awns attaching to animals and fibrous material. Also spread in agricultural produce, hay and pasture seeds and in mud carried by animals and machinery.

Some is spread in animal droppings.

Origin and History:

Central America and possibly Africa.




Open scrub lands and creeks.


Tropical regions with a distinct wet and dry season. Subtropics.


Avoids limestone and seasonally flooded clays.

Plant Associations:

Riverine thickets. Open scrubland.



Jute substitute

Medicinal plant in Asia.


Weed of roadsides, plantations, pastures and cultivated fields, sugar cane, tropical crops and disturbed areas. It competes strongly with crops for light and nutrients. It is one of the most serious weeds of Northern Australia.

Rapidly spreads in over-grazed areas near trees and troughs and as soil fertility builds up.

Stock tend to ignore eating it even though it is nutritious.


Not recorded as toxic.


Noxious weed of NT and WA.

Management and Control:

Sowing vigorous pasture species, reducing grazing and supplying adequate fertiliser reduces the density of the infestation. Pangola Grass, Buffel Grass and Calopo have been used successfully in the NT. Spot spraying with 2,4-D amine can control seedlings. Atrazine also controls seedlings. For older plants slash at the beginning of the wet season followed by spraying of the regrowth two weeks later with 2,4-D amine. Slash all remaining plants prior to seed set to reduce spread. Glyphosate applied by the rope wick applicator is also effective. Stock should not be moved directly from infested to clean areas.


Eradication strategies:

Exclude stock and prevent access when seed is present to prevent spread.

Isolated plants can be mechanically removed if the roots are cut well below the crown. Repeated cultivation provides good control and encourages dormant seed to germinate. Seedlings will need to be controlled for a number of years until the dormant seed bank in the soil is exhausted. Spraying the infested area with 4 L/ha of Atrazine 500g/L and planting triazine tolerant plants will help prevent seedlings establishing.

Herbicide resistance:

Biological Control:

Biological control agents have been released to help control it.

Related plants:

Sand Sida (Sida ammophila)

Tall Sida (Sida calyxhymenia or Sida petrophila)

Flannel Weed (Sida cordifolia)

Corrugated Sida (Sida corrugata)

Ridge Sida (Sida cunninghamii)

Pin Sida (Sida fibulifera)

Fine Sida (Sida filiformis)

Twiggy Sida (Sida intricata)

Hill Sida (Sida phaeotricha or Sida cryphiopetala)

Lifesaver Burr (Sida platycalyx)

Common Sida (Sida rhombifolia)

Shrub Sida (Sida rohlenae)

Spiny Sida (Sida spinosa)

Spiked Sida (Sida subspicata)

High Sida (Sida trichopoda)

Sida goniocarpa

Plants of similar appearance:

Alkali Sida (Malvella leprosa or Sida hederacea or Sida leprosa).


A.P.B. Advisory Leaflet No. 94 (1983).

Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (1997). Western Weeds. A guide to the weeds of Western Australia. (Plant Protection Society of Western Australia, Perth, Western Australia). P176-177. Photo.

Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #1131.1.

Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious weeds of Australia. (Inkata Press, Melbourne). p508-511.


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