Friends of Rietvlei

There are several species of weeds that occur in large numbers in our conservation areas and also in public open spaces and along our roadsides. These are most visible this time of the year as they all flower between August and October.

Residents are encouraged to remove these weeds from their gardens should they occur there. All are invasive and can spread rapidly. The seven species we are most concerned about, are the following:

Echium plantagineum, commonly known as Patterson's Curse, is native to western and southern Europe (from southern England south to Iberia and east to the Crimea), northern Africa, and southwestern Asia.

It has been introduced to Australia, South Africa and United States and is an invasive plant. Due to a high concentration of pyrrolizidine alkaloids in the shoot it is poisonous to grazing livestock, especially those with a simple digestive system like horses. The toxins are cumulative in the liver and death results from too much Paterson's curse in the diet.

Echium plantagineum is a winter annual plant growing to 20–60 cm tall, with rough, hairy, lanceolate leaves up to 14 cm long. The flowers are purple, 15–20 mm long, with all the stamens protruding, and borne on a branched spike.

Echium plantagineum is a Category 1 Declared Weed in terms of the Conservation of Agricultural Resources Act, Act 43 of 1983, and must be removed by landowners.

Argemone mexicana (Mexican poppy or Mexican prickly poppy) is a species of poppy found in Mexico and now widely naturalized in the United States, India and Ethiopia.

The plant has also spread to many other countries where it is considered a nuisance as it

The seeds resemble the seeds of Brassica nigra (mustard). As a result, mustard can be adulterated by argemone seeds, rendering it poisonous. Several significant instances of poisoning have been reported in India, Fiji, South Africa and other countries. 1% adulteration of mustard oil by argemone oil has been shown to cause clinical disease.

Lavatera arborea or Malva arborea, the Tree Mallow, is a species of mallow native to the coasts of western Europe and the Mediterranean region, from the British Isles south to Algeria and Libya, and east to Greece.

Lavatera arborea tolerates sea water to varying degrees, at up to 100% sea water in its natural habitat, excreting salt through glands on its leaves. This salt tolerance can be a competitive advantage over inland plant species in coastal areas.

Tree Mallow seeds may be transported between separated coastal areas by the floating fruit, and seabirds are considered a likely means of spread. The seeds are encased in an impermeable outer case, and can remain viable for years, even after extended immersion in saltwater.

The Tree Mallow's recent increased range in many countries has raised concerns that it is displacing native vegetation. Its spread among Australian islands in recent decades is thought to be reducing biodiversity, soil retention, and seabird habitat.

Rapistrum rugosum is a species of flowering plant in the mustard family known in South Africa as Wild Mustard. It is native to Eurasia and parts of Africa, and it is present throughout the world as an introduced species and a common weed. It is an invasive species in many areas.

In South wild mustard is a major problem in grain-growing areas as it adulterates the seeds of the grains during harvesting, lowering the standard of grain flour

Lupinus, commonly known as Lupins or lupines, is a genus in the legume family (Fabaceae). The genus comprises about 280 species, with major centers of diversity in South and western North America, and the Andes and secondary centers in the Mediterranean region and Africa.

Given that lupin seeds have the full range of essential amino acids and that they, contrary to soy, can be grown in more temperate to cool climates, lupins are becoming increasingly recognized as a cash crop alternative to soy. Three Mediterranean species of lupin, Blue Lupin, White Lupin, and Yellow Lupin are widely cultivated for livestock and poultry feed.

Lupins are popular ornamental plants in gardens. There are numerous hybrids and cultivars. Some species, such as Garden Lupin (Lupinus polyphyllus) and hybrids like the Rainbow Lupin (L. × regalis) are common garden flowers. Others, such as the Yellow Bush Lupin (L. arboreus) are considered invasive weeds when they appear outside their native range.

Vicia benghalensis is a species of vetch known by the common names purple vetch and reddish tufted vetch. It is native to southern Europe, North Africa, and nearby islands, and it is utilized elsewhere in agriculture and may be present in the wild as an introduced species. It is an annual herb with a climbing stem which is coated in hairs, often densely, making the plant appear silvery white.

This plant is used as a cover crop and green manure for the purposes of soil improvement and weed and pest control. It is used in crop rotation, for hay and fodder, and as a honey plant, and it has a very high biomass yield.

The vetches grown as forage are generally toxic to non-ruminants (such as humans), at least if eaten in quantity. Cattle and horses have been poisoned by Vicia villosa and Vicia benghalensis, two species that contain canavanine in their seeds.

Euphorbia is a genus of plants with over 2000 species, it is one of the most diverse genera in the plant kingdom, exceeded possibly only by Senecio. Members of the family and genus are known as milkweeds due to the milky sap exuded by the plant when damaged. The genus is primarily found in the tropical and subtropical regions of Africa and the Americas, but also in temperate zones worldwide. Succulent species originate mostly from Africa, the Americas and Madagascar.

The latex (milky sap) acts as a deterrent for herbivores as well as a wound healer. As it is under pressure, it runs out from the slightest wound and congeals within a few minutes of contact with the air. In contact with mucous membranes (eyes, nose, mouth) the latex can produce extremely painful inflammation. Euphorbias should thus be handled with caution.