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Scientific Name
Synonyms
Family
Common Names
Origin
Naturalised Distribution
Habitat
Habit
Distinguishing Features
Stems and Leaves
Flowers and Fruit
Reproduction and Dispersal
Environmental Impact
Legislation
Management
Similar Species
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Click on images to enlarge

infestation (Photo: Sheldon Navie)

upright habit with narrow leaves (Photo: Chris Gardiner)

spreading habit with broader leaves (Photo: Sheldon Navie)

relatively broad lower leaves with toothed margins (Photo: Sheldon Navie)

upper leaves and flowers (Photo: Sheldon Navie)

close-up of broader lower leaves and flower buds borne on short stalks (Photo: Sheldon Navie)

narrow upper leaves and flower buds (Photo: Chris Gardiner)

close-up of flower (Photo: Sheldon Navie)

immature and mature fruit, sometimes in clusters in the upper leaf forks (Photo: Sheldon Navie)

close-up of immature fruit (Photo: Sheldon Navie)

close-up of mature fruit (Photo: Sheldon Navie)

close-up of 'seeds', each with two spiny awns (Photo: Sheldon Navie)

Sida acuta

Scientific Name

Sida acuta Burm. f.

Synonyms

Sida acuta Burm. f. subsp. carpinifolia (L.f.) Borss. Waalk.
Sida carpinifolia L. f.

Family

Malvaceae

Common Names

broom grass, broom weed, broomweed, cheese weed, cheeseweed, clock plant, common fanpetals, common wireweed, morning mallow, sida, southern sida, spiny-head sida, spinyhead sida, spiny-headed sida

Origin

This species may have originated in Central America, but it is now widespread throughout the tropical and sub-tropical regions of the world (i.e. pan-tropical).

Naturalised Distribution

Widely naturalised throughout the northern parts of Australia. It is most common in the coastal regions of central and northern Queensland and in the northern parts of the Northern Territory. Relatively common throughout the northern regions of Western Australia and other parts of northern Queensland. Also recorded in other parts of the Northern Territory, in south-eastern Queensland, in the coastal central districts of New South Wales and on several offshore islands (i.e. Norfolk Island, Christmas Island and the Cocos Islands).

Widely naturalised overseas, including in eastern Asia (i.e. China and Taiwan) and on several Pacific islands (e.g. the Galápagos Islands, the Chuuk Islands, Fiji, French Polynesia, Guam, Hawaii, Kiribati, the Marshall Islands, Nauru, New Caledonia, Niue, Palau and the Solomon Islands).

Habitat

A weed of tropical, semi-arid and occasionally also sub-tropical and warmer temperate regions. It invades open woodlands, pastures, waterways (i.e. riparian vegetation), plantations, crops, gardens, disturbed sites, roadsides and waste areas.

Habit

A long-lived (i.e. perennial) herbaceous plant or small shrub (i.e. sub-shrub) usually growing 30-100 cm tall, but occasionally reaching up to 1.5 m in height. However, it often behaves as a short-lived (i.e. annual) plant in the wet-dry savannas of northern Australia.

Distinguishing Features

Stems and Leaves

The slender, yet wiry or slightly woody, stems are branched and either upright (i.e. erect) or spreading (i.e. ascending) in nature. They are sparsely covered with fine, star-shaped (i.e. stellate), hairs.

The leaves are alternately arranged along the stems and borne on short, hairy (i.e. pubescent) stalks (i.e. petioles) 3-7 mm long. These yellowish-green coloured leaves (12-95 mm long and 3-40 mm wide) are usually elongated in shape (i.e. lanceolate) with toothed (i.e. crenate or serrate) margins and pointed tips (i.e. acute or acuminate apices). They are hairless (i.e. glabrous) or sparsely covered in simple or star-shaped (i.e. stellate) hairs.

Flowers and Fruit

The yellow (rarely whitish) flowers (1-2 cm across) are borne singly or in small clusters in the upper leaf forks (i.e. axils). They are borne on short and slender stalks (i.e. peduncles) 2-8 mm long, that elongate up to 15 mm in fruit. Each flower has five pale yellow, yellow, or pale orange petals (6-9 mm long) and five mostly hairless sepals (5-8 mm long). These pale green sepals are fused together at the base (i.e. into a calyx tube) and have pointed tips (i.e. acute calyx lobes). The flowers also have numerous (about 100) tiny stamens, with their bases fused to each other, and an ovary topped with a style that is divided into 6-10 branches near its tip. Flowering occurs mostly during late summer, although it may occur throughout the year if conditions are favourable.

The fruit is a hard structure (i.e. schizocarp) that turns from green to dark brown as it matures. These small fruit (2-6 mm across and 3-5 mm high) break up into 5-8 one-seeded segments (i.e. mericarps) when fully mature. These 'seeds' (i.e. mericarps) are wedge-shaped (1.5-2 mm long) and topped with two sharp awns (0.5-1.5 mm long). The true seeds are inside these mericarps, they are smaller (about 1.5 mm long) and reddish-brown to black in colour.

Reproduction and Dispersal

This species reproduces by seed, which readily attach to animals, clothing and other materials. Seeds may also be dispersed in mud and contaminated agricultural produce.

Environmental Impact

Spiny-head sida (Sida acuta) is regarded as an environmental weed in northern Australia (i.e. northern Queensland, the northern parts of the Northern Territory and northern Western Australia).

Legislation

This species is declared under legislation in the following states and territories:

Management

For information on the management of this species see the following resources:

Similar Species

Spinyhead sida (Sida acuta) can be confused with spiny sida (Sida spinosa), common sida (Sida rhombifolia), flannel weed (Sida cordifolia), spiked sida (Sida subspicata), spiked malvastrum (Malvastrum americanum) and prickly malvastrum (Malvastrum coromandelianum). These species can be differentiated by the following differences: