Trianthema portulacastrum in the EPPO region: addition to the EPPO Alert List
Why
Trianthema portulacastrum has been spreading in tropical and subtropical areas worldwide. The species is considered to have a wide native range including the Americas, Asia and Africa. It is a C4 weed in fodder crops, in summer crops (such as soybean, cotton, rice, peanut and tomato) and in horticulture. Considering the potential economic impact of the species it has been decided to add it to the EPPO Alert List. Further information on the presence of the species in Mediterranean countries would be needed to make an assessment of the species in the EPPO region.
Geographical distribution
EPPO region: Israel, Jordan.
Asia: Cambodia, China, India, Indonesia, Iran, Myanmar, Nepal, Pakistan, Philippines, Qatar, Sri Lanka, Saudi Arabia, Thailand, Vietnam.
Africa: Côte-d'Ivoire, Egypt, Ethiopia, Gambia, Ghana, Kenya, Mali, Mozambique, Niger, Nigeria, Senegal, Sudan, Tanzania, Togo, Yemen.
North America: Mexico, USA.
Central and South America: Colombia, Costa Rica, Ecuador, Guatemala, Honduras, Nicaragua, Peru, Puerto Rico, Venezuela.
Oceania: Australia.
Morphology
Annual, succulent, usually glabrous.
Stems: prostrate or decumbent, diffusely branched, to 1 m; young branches with lines of minute hairs proximal to petioles.
Leaves: unequal pairs alternating along stem; stipules dilated at base; petiole usually equalling blade; blade elliptic to orbiculate, to 4 cm, apex obtuse, often notched, or apiculate.
Inflorescences: flowers usually solitary, sessile, in axils of smaller leaves (bracts) of some pairs, partly covered by sheathing stipule of bracts; bracteoles connate, 1-1.5 mm, apex acute.
Flowers: calyx 3-5 mm; calyx lobes purple or white adaxially, lanceolate, 2.5 mm; stamens 5-10.
Capsules: cylindric, sometimes curved, 4-5 mm, corky, basal portion appearing embedded in stem, apical portion containing 1 seed; apical wings 2, prominent, erect, crestlike.
Seeds: 4 to 15 seeds per capsule, dull reddish brown to black, ridged, 1.5-2 mm.
Biology and Ecology
An extended germination period is reported from wet and irrigated habitats in East-Asia. The bisexual flowers are insect pollinated. Seeds are dispersed by water (hydrochory) and near the parent plant (autochory). Seeds may be dormant for few months.
Habitats
Ruderal habitats gardens, roadside, lakes, riverbanks, creeks, coastal areas, agricultural habitats.
Pathways for movement
There are reports of spice seed imports being contaminated with T. portulacastrum. It might therefore be associated with grain importation, as well as with water and soil movement.
Impacts
Significant yield losses attributed to the weed have been reported in maize, soybean, peanut and mung bean. In Israel, in the Galilee Valleys yield reduction in summer crops (peanut, tomato and watermelon) has been observed. In Saudi Arabia, the species is regarded as a highly invasive species.
Control
Chemical methods, both pre- and post-emergence can be used against the species. For mechanical methods, the plant should be controlled at the seedling stage. Hand weeding and hoeing can be used (in maize, pearl millet and cowpea fields) and also inter - row mechanical cultivation (in cotton and sugarcane). Sorghum, sunflower, brassicas and mulberry are considered effective competitors that can inhibit the germination of T. portulacastrum.
Sources
Flora of North America. http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=220013693
Hatem Taifour and Ahmed El-Oqlah (2016) Annotated Checklist of the Vascular Plants of Jordan, RBG. Edt. Shahina Ghazanfar. Kew Publishing http://jo.chm-cbd.net/biodiversity/species-diversity/flora-jordan/flora-checklists/annotated-checklist-vascular-plants-jordan-rbg
Kwesi Ampong-Nyarko, De Datta SK (1991) A Handbook for Weed Control in Rice. p 25. International Rice Research Institute, Philippines.
Kumar Manpreet, Kumar Aggarwal Neeraj (2017) Trianthema portulacastrum L.- the noxious weed and its control. Advances in Plants & Agricultural Research 6(3), 62‒64.
Lee J, Chauhan B, Johnson D (2011) Germination of fresh horse purslane (Trianthema portulacastrum) seeds in response to different environmental factors. Weed Science 59(4), 495-499.
Thomas J, El-Sheikh MA, Alfarhan AH, Alater AA, Sivadasan M, Basahi M, Al-Obaid S (2016) Impact of alien invasive species on habitats and species richness in Saudi Arabia. Journal of Arid Environments 127, 53-65.