Click on images to enlarge
infestation (Photo: Sheldon Navie)
creeping habit (Photo: Sheldon Navie)
habit growing on a fence (Photo: Sheldon Navie)
close-up of stem and leaf with slightly-lobed leaflets (Photo: Sheldon Navie)
flowers (Photo: Sheldon Navie)
close-up of flowers (Photo: Sheldon Navie)
immature fruit (Photo: Sheldon Navie)
mature fruit (Photo: Sheldon Navie)
close-up of seeds (Photo: Steve Hurst at USDA PLANTS Database)
seedlings (Photo: Sheldon Navie)
Macroptilium atropurpureum (DC.) Urban
Phaseolus atropurpureus DC.
atro, atro siratro, cowpea, macroptilium, phasey bean, purple bean, purple bush-bean, purple bushbean, siratro
Fabaceae (Queensland, the ACT, Victoria, Tasmania, and the Northern Territory)Fabaceae: sub-family Faboideae (New South Wales)Leguminosae (South Australia)Papilionaceae (Western Australia)
Native to southern USA (i.e. Texas), Mexico, Central America (i.e. Belize, El Salvador, Guatemala, Honduras, Nicaragua and Panama), the Caribbean and northern South America (i.e. French Guiana, Brazil, Colombia, Ecuador and Peru).
Widely naturalised in the northern parts of Australia, particularly in wetter coastal districts. It is common and widespread in eastern and northern Queensland, in north-eastern New South Wales, in the northern parts of the Northern Territory and in the Kimberley region in northern Western Australia. Occasionally naturalised in the inland parts of Queensland and the Northern Territory, along the central coast of New South Wales and near Perth in south-western Western Australia. Also naturalised on Christmas Island, Lord Howe Island and the Cocos Islands.
Widely cultivated in tropical regions, in central and south-eastern Queensland and in north-eastern New South Wales as a pasture plant. The cultivar 'Siratro' is by far the most well known, but the more recently developed 'Aztec' cultivar is also common in cultivation.
A weed of disturbed sites, waste areas, roadsides, fences, gardens, coastal environs, urban bushland, watercourses (i.e. riparian areas) and plantation crops (e.g. sugar cane). It is primarily found in high rainfall tropical and sub-tropical coastal areas but is occasionally also present in warmer temperate regions and in wetter habitats in semi-arid and arid inland areas.
- a robust creeping herbaceous plant or climbing vine with hairy stems.
- its leaves are compound with three slightly-lobed leaflets.
- its pea-shaped flowers are dark reddish-purple or blackish-purple in colour.
- its fruit are slender pods up to 10 cm long.
A long-lived (i.e. perennial) herbaceous plant with creeping (i.e. decumbent) or climbing stems usually growing 2-3 m long. It stems may occasionally reach up to 5 m in height when climbing up over taller vegetation.
Stems and Leaves
The stems are ribbed lengthwise and hairy (i.e. pubescent). Older stems at the base of older plants are fibrous and about 5 mm thick, while younger stems are slender (1-2 mm thick) and green in colour.
The compound leaves (6.5-12 cm long) each have three leaflets (i.e. they are trifoliate). These leaves are alternately arranged along the stems and borne on stalks (i.e. petioles) 2-5 cm long. Individual leaflets (2-7 cm long and 1-5 cm wide) are almost oval (i.e. elliptic), egg-shaped in outline (i.e. ovate) or somewhat diamond-shaped (i.e. rhombic), but the two side (i.e. lateral) leaflets on each leaf are usually slightly lobed. They otherwise have entire margins and their undersides are usually densely hairy (i.e. pubescent). There is also a pair of small leafy appendages (i.e. stipules) 3-5 mm long at the base of each leaf stalk (i.e. petiole).
Flowers and Fruit
The pea-shaped flowers are dark reddish-purple or reddish-black in colour and several (6-12) are crowded toward the tips of long flower stalks (i.e. peduncles) 10-30 cm long. Each flower (1.5-2.6 cm long) is borne on a very short stalk (i.e. pedicel) 1-2 mm long. They have a small upper petal (i.e. standard), two large side petals (i.e. wings) and two pinkish lower petals that are fused together (i.e. into a keel) and strongly twisted or coiled. They also have five small green sepals (5-10 mm long) that are fused together at the base in to a short tube (i.e. calyx tube), ten stamens, and an elongated ovary topped with a style and stigma. Flowering occurs throughout the year.
The long and narrow (i.e. linear) pods are cylindrical and turn from green to brown in colour as they mature. These pods (5-10 cm long and 3-5 mm wide) are shortly hairy (i.e. pubescent) and split open when mature to release about 12 seeds. The seeds (about 4 mm long and 2 mm wide) are somewhat egg-shaped (i.e. ovoid) or slightly kidney-shaped (i.e. reniform) and speckled light brown and black.
Reproduction and Dispersal
This species reproduces by seed. Seeds are forcibly ejected from the pod when mature, and can be thrown for several metres. They can also be dispersed greater distances through water movement and following ingestion by cattle.
Siratro (Macroptilium atropurpureum) is regarded as an environmental weed in Queensland, the Northern Territory, northern Western Australia and northern New South Wales. It is listed as a priority environmental weed in at least one Natural Resource Management region and is actively managed by community groups in the Northern Territory. This species can form dense infestations along forest margins, and will grow over native shrubs, grasses and young trees, effectively smothering them.
Siratro (Macroptilium atropurpureum) is currently of most concern in south-eastern Queensland, where it is ranked among the top 50 environmental weed species and appears on numerous local environmental weed lists (e.g. in Gold Coast City, Ipswich City and Redlands Shire). It has also invaded riparian vegetation and coastal sand dune vegetation in this region and is a problem in revegetation sites, where it smothers young trees and shrubs before they become established. However, siratro (Macroptilium atropurpureum) is also of concern in many other parts of Queensland (e.g. in the Burdekin rangelands, in the wet tropics bioregion and a troublesome environmental weed encountered in rehabilitation projects in the Townsville region).
In Western Australia it grows along creek lines and drains in the Kimberley region, especially around Lake Kununurra, while in New South Wales it is mainly naturalised in pastures and along roadsides north from the Sydney region.
- siratro (Macroptilium atropurpureum) is a creeping or climbing plant with dark purple-red flowers.
- phasey bean (Macroptilium lathyroides ) is an upright plant (usually less than 1 m tall) with bright red flowers.
Siratro (Macroptilium atropurpureum) is also very similar to burgundy bean (Macroptilium bracteatum), which is also cultivated in Australia and sparingly naturalised in tropical Queensland. However, burgundy bean (Macroptilium bracteatum) differs by having a cluster of small leafy bracts near the base of each of its flower stalks (i.e. peduncles).
Not declared or considered noxious by any state government authorities.
For information on the management of this species see the following resources:
- the Biosecurity Queensland Fact Sheet on this species, which is available online at http://www.dpi.qld.gov.au.
Anonymous (2002). A Global Compendium of Weeds. http://www.hear.org/gcw. Hawaiian Ecosystems at Risk Project and Department of Agriculture - Western Australia.
Anonymous (2002). Australia's Virtual Herbarium. http://www.anbg.gov.au/avh. Australian National Botanic Gardens, Environment Australia, Canberra, ACT.
Anonymous (2006). Germplasm Resources Information Network (GRIN). http://www.ars-grin.gov/cgi-bin/npgs/html/index.pl. National Germplasm Resources Laboratory, National Genetic Resources Program, Agricultural Research Service (ARS), United States Department of Agriculture (USDA), Beltsville, Maryland, USA.
Anonymous (2006). Macroptilium atropurpureum (DC.) Urb., Fabaceae. Pacific Island Ecosystems at Risk (PIER): plant threats to Pacific ecosystems. http://www.hear.org/pier/species/macroptilium_atropurpureum.htm. Institute of Pacific Islands Forestry, Hawaii, USA.
Anonymous (2006). Siratro. Macroptilium atropurpureum. Natural Resources and Water Facts - pest series, PP93. The State of Queensland (Department of Natural Resources and Water), Brisbane, Queensland.
Auld, B.A. and Medd, R.W. (1996). Weeds: an illustrated botanical guide to weeds of Australia. Inkata Press, Sydney, New South Wales.
Batianoff, G.N. and Butler, D.W. (2002). Assessment of invasive naturalized plants in south-east Queensland. Plant Protection Quarterly 17: 27-34.
Cook, B.G., Pengelly, B.C., Brown, S.D., Donnelly, J.L., Eagles, D.A., Franco, M.A., Hanson, J., Mullen, B.F., Partridge, I.J., Peters, M. and Schultze-Kraft, R. 2005. Tropical Forages: an interactive selection tool. CD-ROM. CSIRO Sustainable Ecosystems (CSIRO), Department of Primary Industries and Fisheries (DPI&F Queensland), Centro Internacional de Agricultura Tropical (CIAT) and International Livestock Research Institute (ILRI), Brisbane, Queensland.
Gardner, C. and Murray, L. (2007). Macroptilium atropurpureum (DC.) Urb. PlantNET - New South Wales Flora Online. http://plantnet.rbgsyd.nsw.gov.au. The Plant Information Network System of the Royal Botanic Gardens and Domain Trust, Sydney, New South Wales.
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. The Plant Protection Society of Western Australia, Victoria Park, Western Australia.
Kleinschmidt, H.E., Holland, A. and Simpson, P. (1996). Suburban Weeds. 3rd Edition. Department of Primary Industries, Brisbane, Queensland.
Navie, S.C. (2004). Crop Weeds of Australia. CD-ROM. The University of Queensland, St. Lucia., Queensland.
Navie, S.C., Markwell, B., Playford, J. and Adkins, S.W. (2002). Suburban and Environmental Weeds: an interactive identification and information system. CD-ROM. The University of Queensland, St. Lucia, Queensland.
Spooner, A., Carpenter, J., Smith, G. and Spence, K. (2007). *Macroptilium atropurpureum (Moc. & Sesse) Urb. Purple bean. FloraBase: The Western Australian Flora. http://florabase.calm.wa.gov.au. Western Australian Herbarium, Department of Conservation and Land Management (CALM), Perth, Western Australia.
Stanley, T.E. and Ross, E.M. (1986). Flora of South-eastern Queensland. Volume 2. Department of Primary Industries, Brisbane, Queensland.