APC (2021). Australian Plant Census. Council of Heads of Australasian Herbaria (CHAH). Available at: https://biodiversity.org.au/nsl/services/apc. [accessed 20/08/2021].
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Spiny Emex (Rumex hypogaeus) is a somewhat fleshy annual herb, prostrate (lying flat on the ground) sometimes with branches growing horizontally but turned up at the ends, that grows up to 40 cm high, with stems up to 60 cm long from a central growing point. Its leaves are triangular to egg-shaped, 2–9 cm long and 1–6 cm wide, with undulating margins. The leaf stalk is 2–10 cm long and normally longer than leaf-blade, and surrounded at its base by a short membranous sheath.
Flowers are either male or female and occur on the same plant in clusters in the leaf forks. The male inflorescence (flower spikes) are about 2–7 cm long with flower segments or perianth (inner segments petals and and outer segments calyx that are similar in appearance) are about 2 mm long, stalked, and are not spiny. The female inflorescence in small clusters of flowers are not stalked 0.7–1.1 cm long, 0.4–0.6 cm wide at the widest point and have three very sharp, rigid, laterally spreading spines, arranged at a 120° angle to each other. In fruit (the fruiting perianth), these spines harden and turn brown.
The ripe fruit about 1–1.1 cm long and 4–6 mm wide at the widest point, (just below the spines). Spines to 0.5 cm long. Seeds or the nut are hidden and retained within the hard woody fruiting perianth (fruit) (Wilson 2000; Parsons & Cuthbertson 2001). The nut is ovate (shaped like a section through the long axis of an egg) to broadly triquetrous (triangular in cross-section, but acutely angled with 3 distinct longitudinal ridges), 4–5 mm long, brown, smooth.
For further information and assistance with identification of Spiny Emex contact the herbarium in your state or territory.
Spiny Emex occurs in sub-humid and semi-arid subtropical and temperate regions. It grows mainly on sandy and loamy soils, and less frequently on clays and in a wide range of vegetation types. It is often found around disturbed areas such as sheep yards, saleyards, roadsides and areas of habitation. It is a widespread weed of grazing and cropping lands but also grows in natural areas especially in drier inland regions, in woodlands, mallee, shrubland, grassland and herb fields, usually in open or disturbed areas such as ephemeral drainage lines, dry creek beds, lake edges, floodplains, riverbanks, salt scalds, bare areas and disturbed sites (Stanley & Ross 1983; Cunningham et al. 1992; Keighery 1996; Parsons & Cuthbertson 2001; Western Australian Herbarium 2007).
The closely related and less common species Lesser Jack (Rumex spinosa) coexists with Spiny Emex in some areas and there is evidence of hybridisation.
Lesser Jack habit: differs from Spiny Emex and is [more] erect. It also has smaller fruit with shorter spines. Lesser Jack fruits are: 0.4–0.7 cm long and 3–4 mm wide at the top, with spines 1–2 mm long.
Spiny Emex habit: grows close to and along the ground with the end of the branches sometimes erect (not the whole plant erect) with larger fruits. Spiny Emex size are: 0.7–1.1 cm long and, 0.4–0.5 cm wide, with the spines are 2-5 mm long (Wilson 2000; Parsons & Cuthbertson 2001).
Spiny emex (Rumex hypogaeus) is a common weed of agricultural areas, particularly crops, and disturbed habitats (e.g. roadsides, tracks, firebreaks, picnic sites, old homesteads and clearings). However, it is often present in highly disturbed sites in conservation reserves and also invades natural areas including creekbanks, river floodplains, claypans, the edges of saline lakes and granite rock areas. It is a serious weed of crops and pastures.
Agriculture: Spiny Emex is a weed of pasture and cultivation. It can reduce crop yields (particularly cereals) and pasture productivity by competition, as it is fast growing and the prostrate growth smothers more desirable species such as legumes. Infestations of spiny emex can be very dense and counts of more than 900 plants per square metre have been made in Western Australia. South Australian studies show that an infestation of about 11 plants per square metre reduces wheat yields by almost 40% (Agriculture Victoria 2021). Major impact on quantity of produce It is also a serious weed of dried grapes, as the spiny fruit can become mixed with grapes on drying racks and they are difficult to grade out (Chorney 1986; Parsons & Cuthbertson 2001; Sainty and Associates 2005; Land Protection 2006). Spiny emex contains oxalates in the leaves which are toxic to ruminants especially sheep (DPI NSW 20219). Stock rarely eat Spiny Emex, but it has been suspected of stock poisoning on some occasions. The plant can contain potentially toxic levels of oxalates at levels that are sufficiently high to poison sheep or cattle if the animals were forced to eat large amounts when very hungry (Everist 1974; Stanley & Ross 1983; Cunningham et al. 1992; Parsons & Cuthbertson 2001). The sharp-pointed fruits are troublesome to animals such as dogs and sheep, and the spiny fruits can cause lameness. Sheep have developed blackleg from infection of wounds to the feet caused by the spiny fruits.
Native ecosystems: Spiny Emex also occurs as a weed in national parks and nature reserves, usually in disturbed sites such as roads, tracks, firebreaks, picnic areas, old homesteads and clearings. However, it can also impact on biodiversity and the environment by invading natural areas such as the edges of creeks, riverine flats, alluvial flats (claypans, edges of saline lakes) and rocky areas (Keighery 1996).
Urban areas: The Spiny fruits can also puncture small tyres, such as those of bicycles, and restrict the use of recreation areas, particularly where people are bare-footed and spines can penetrate light footwear (Cunningham et al. 1992; Parsons & Cuthbertson 2001; Sainty and Associates 2005; VicFora 2016).
Spiny Emex is spread by seed. The fruits containing the seeds are readily dispersed when their spines become attached to almost anything that passes over, or is placed on, them, particularly shoes, rubber tyres, feet of animals or containers of produce. The spiny fruits are structured so that a spine is always pointing up, which aids in dispersal (Government of South Australia 2021). It is also spread through contamination of fodder, particularly lucerne hay, as well by fruits in poorly graded clover seed and imported feed wheat. The fruits also float on water and are spread along watercourses and with floods (Scott 1990; Scott et al. 1996; Parsons & Cuthbertson 2001).
The introduction and spread of Spiny Emex in Australia appears to have started in 1830 in Western Australia, from where it apparently spread to other states. It was probably brought in from Africa for use as a vegetable or as a contaminant of stock feed, or attached to clothing, equipment, or shoes (Weiss & Simmons 1979; Scott et al. 1996; Gilbey et al. 1998; Parsons & Cuthbertson 2001).
The high levels of seed dormancy (more than 4 years in some cases) and longevity make Spiny Emex hard to eradicate
Non-chemical control: Small infestations and isolated plants of Spiny Emex can be grubbed out or manually removed. If the plants are seeding then they should be completely destroyed by burning them.
Small areas should be fenced off to prevent stock, people and vehicles spreading the seed. For large areas infested with Spiny Emex, shallow cultivate in late summer to encourage germination in autumn and then kill the seedlings with cultivation or herbicides. Deep ploughing is not recommended because it buries seed and induces dormancy, which may be broken when the seeds are returned to the surface in following seasons. Any control program must aim at killing all plants shortly after emergence, and needs to be continued for several years (Parsons & Cuthbertson 2001). 'Prickle rollers' have been developed to gather and remove surface Spiny Emex fruit from drying greens in vineyards (Parsons & Cuthbertson 2001).
Chemical control: Cultivation kills seedlings, and can be effective when combined with chemical control (Gilbey et al. 1998; Parsons & Cuthbertson 2001; Land Protection 2006). Herbicides are effective but do not eradicate the problem due to seed bank Herbicides can be used in agricultural, horticultural, and urban environments for cereal and other crops, pastures and roadside and bushland.
See the Australian Pesticides and Veterinary Medicines Authority for chemical information http://www.apvma.gov.au
Biological control: A weevil (Perapion neofallax) was released and has become established at a few sites, but it has had little to no impact on controlling Spiny Emex.
Spiny Emex is an annual. It flowers throughout much of the year, though mainly in the warmer months in spring and summer (Stanley & Ross 1983; Cunningham et al. 1992; Parsons & Cuthbertson 2001). Seeds germinate in winter-spring, although seedlings can appear at any time of the year when soil moisture is adequate, and there can be up to six waves of germination in one year. Early seedling development is rapid, especially in cultivated soil, and most growth occurs in the warmer months, with plants persisting until late summer or early autumn under favourable conditions. Seedling survival and plant persistence is aided by a well-developed deep taproot (Cunningham et al. 1992; Gilbey et al. 1998; Parsons & Cuthbertson 2001).
Present in all states and territories.
Spiny Emex is present in all mainland states (Weiss & Simmons 1979; Scott 1990; Scott et al. 1996; Parsons & Cuthbertson 2001), and a widespread weed in New South Wales, South Australia and Western Australia, but largely absent from tropical areas. It is only recorded from the southern part of Queensland apart from several collections from west of Cairns. IN the Northern Territory it s recorded from the southern part of the state and around Alice spring. In Victoria its has been collected from a diversity of areas in and around Melbourne. A collection from the Australian Capital Territory was from hay imported from Mildura in Victoria, and an old collection from the 1940s exists from Tasmania (AVH 2021).
Spiny Emex is native to southern Africa (Wilson 2000), where it is widespread and regarded as a weed of cereal crops and vineyards in South Africa (Parsons & Cuthbertson 2001).
NT, SA, TAS, VIC
Emex centropodium Meisn.
Emex australis Steinh.
Doublegee, Double Gee, Double-gee, Three Corner Jack, Three-cornered Jack, Goat's Head Burr, Goathead, Jackie, Prickly Jack, Cape Spinach, Devil's Face, Devil's Thorn, Bullhead, Bull Head, Cat's Head