Sida acuta

wire weed


Sida acuta

Burm.f. 1768

pronounced: SEE-duh uh-KEW-tuh

(Malvaceae — the hibiscus family)


common names: wire weed, spiny-headed sida

Sida comes from the Greek word σιδη (sidé), used in classical times as a common name for both the pomegranate and the yellow water-lily Nuphar luteum; acuta is from the Latin acutus, sharpened, describing the leaves.
This little shrub, a native of tropical America and now a pan-tropical plant, is a problem in pastures and sugarcane in central to northern coastal Queensland, in pastures in the NT and in the Ord River district in WA. It is unpalatable and invasive, competing with and excluding native plants as well as pasture and crop species. It can infest areas where degraded, disturbed and improved soils occur, as well as crops and domestic gardens. The seeds adhere to fur and clothing, making it easy to spread. The seeds can also spread as impurities in hay and pasture seed, as well as on hooves, shoes and vehicles. They will germinate even after being eaten by stock and passing through their digestive systems, and they can persist for long periods of time: seedlings can appear years after mature plants have been removed.

It is an erect perennial (sometimes annual) shrub growing to a maximum height of about 1.5 m. The stems are woody, branching several times, and the plant has a strong, well-developed tap root, which is also branched.
The stems are fibrous to woody with tough stringy bark, hairless or sparsely covered with stellate hairs.

The leaves are lanceolate, tapered at both ends, with serrate margins. They are 2 – 9 cm long and 0.5 – 4 cm wide, on petioles 3 – 7 mm long, with 2 unequal stipules at the base.

The flowers, 1 – 2 cm across, are yellow or pale orange (rarely whitish), usually solitary or in pairs. They are borne on short and slender peduncles. They have 5 petals 6 – 9 mm long, and 5 pale green sepals that are fused together at the base into a calyx tube. There are numerous tiny stamens (about 100), with their bases fused to each other, and an ovary topped with a style that is divided into 6 – 10 branches near its tip.

The fruit is a schizocarp that turns from green to dark brown as it matures. These small fruits (2 – 6 mm across and 3 – 5 mm high) break up into 5 – 8 mericarps when fully mature. These ‘seeds’ are wedge-shaped (up to 2 mm long) and topped with 2 sharp awns (0.5 – 1.5 mm long). The true seeds are inside these mericarps, and reddish brown to black in colour.

Photographs taken in Picnic Bay 2014
Page last updated 3rd April 2019