Donkey weed (scientific name Stylosanthes hamata) is a flowering plant belonging to the genus Stylosanthes in the legume family - Fabaceae. Stylosanthes comprises many very important species that are found growing in pastures and forage.
Donkey weed or Stylosanthes hamata is a sub-shrub (shrub-like plant) or herb which grows perennially. In other words, this plant grows year after year. However, donkey weed can also be an annual plant.
Stylosanthes hamata is native to south-eastern region of the USA (especially Florida), the Caribbean, Central America (especially Nicaragua and Guatemala), and tropical South America (countries like Colombia, Brazil, Venezuela and Peru). There was a time when this plant was extensively naturalized in the northern regions of Australia (especially naturalized in the northern and eastern parts of Queensland, in northern and north-western regions of Western Australia and the northern and central regions of the Northern Territory).
This herb is a semi-erect perennial or annual tropical legume that has a very short life-span. Donkey weed can grow up to a height of 75 cm. It has slender stems, multiple branches as well as non-deterinate, while the leaves are pubescent on one side. On the other side they are without bristles - very different from the Townsville stylo (scientific name Stylosanthes humilis), which has several bristles. The leaves of donkey weed are shiny and trifoliate. The lanceolate leaves measure anything between 19 mm and 37 mm in length and 3 mm and 6 mm wide.
The inflorescence of donkey weed comprises a dense head that contains anything between eight and 14 small yellow blooms. The flowering season of this species starts in February and the plants continue to bloom till the soil remains moist. Once the soil dries up, the plants stop flowering. The flowers give way to pods comprising two single-seeded compartments that separate readily. The higher section includes a somewhat curly hook or beak that measures anything between 6 mm and 8 mm in length. On the other hand, the lower section is without any hook.
The kidney-shaped, deep brown seeds of donkey weed are very small measuring 2 mm and 5 mm. One kg pods contain roughly 270,000 seeds. About 450,000 seeds without the pods weight 1 kg. Another species called Caribbean stylo (Stylosanthes hamata) has close resemblance to the species Townsville stylo (Stylosanthes humilis). However, the most striking differences between the other species and Townsville stylo is that the stem of the latter is covered with long hairs (bristles) and the pods of this species are comparatively longer measuring anything between 9 mm and 11 mm and have an elongated beak (hook).
The pods of this species are single-seeded and erect. They are segmented. The upper segment of the pod is glabrous and has a beak (hook) and it measures anything between 6 mm and 7 mm long counting the hook’s length. The kidney-shaped seeds are molted, deep brown and measure 2 mm to 2.5 mm in length. In fact, donkey weed has a numerous varieties of genotypes each different from the other in their ploidy. The Diploid type of donkey weed can adapt to different latitudes, rainfall ranges and altitudes compared to the tetraploid varieties. Two tetraploid cultivars of donkey weed (Amiga in 1988 and Verano in 1973) were released in Australia as pasture legumes. Compared to the Verano cultivar, Amiga produces additional perennial plants as well as seeds when grown in drier and cooler locations. It is worth mentioning here that generally diploid genotype of donkey weed is not cultivated as pasture legume.
Stylosanthes hamata or donkey weed is used extensively to enhance the flora of leys and natural pastures with a view to create a forage bank. All kinds of livestock actually relish the donkey weed. Primarily, the donkey weed is used to create permanent pastures. However, it is also used in cut-and-carry systems to feed livestock fresh fodder. Moreover, this plant can also be used in the form of hay if the plants have been harvested before they have dropped their leaves in the arid season. The donkey weed is a important legume and can be sown easily in pastures. After the harvested plants are sprayed with herbicides, they can also be used in the form of mulch.
Donkey weed is an important, but rare therapeutic herb which can be perennial as well as annual. While this herb is indigenous to the two Americas, presently it is also grown in the Caribbean, especially Jamaica. The donkey weed is generally used as a nutritious animal fodder and, hence, the name of the herb. Moreover, this plant is also used for treating a number of health issues like fever, dizziness and kidney problems.
Some women use this herb as a remedy for teething problems of their babies. The donkey weed herb can also be used for treating arthritis. A sap collected from the donkey weed herb can be effective in getting rid of warts, moles and a number of other skin problems.
The Amiga and Verano cultivars of donkey weed have been successfully used as pasture legume, especially in the arid pastures in northern Australia as well as in India, Nigeria, Thailand and several countries in western Africa. Fruit-bearing donkey weed plants can be harvested and fed to cattle in the form of a protein supplement during the dry months as this plant bears fruits quite early and its seeds are rich in protein content. It has been proved that the Verano cultivar of donkey weed is a useful cover crop and can be grown within cash crops kike sorghum, kenaf, cassava and maize. This legume crop effectively suppresses weed, controls soil erosion and enriches the soil with nitrogen. Verano special pastures like those created on rice paddy banks and even roadsides have proven to be very successful in northeast Thailand.
In fact, rice stubble grazing is a low nutrient feed. But supplementing it with donkey weed pastures created on paddy banks have helped to enhance the nutrient content of cattle feed.
The donkey weed (Stylosanthes hamata) can grow on various types of soils, which include lighter, inferior quality soils. It can also adapt to humid areas having very high rainfall. It can establish itself around settlements, disturbed areas and along roadsides.
This sub-shrub is capable of tolerating drought and, if not grazed, can stay alive even in prolonged dry seasons. The plant tends to drop its leaves after the end of the wet (rainy) season. After it has shed its leaves, only the plants bare green stems can be seen standing. The leaves that fall on the ground are vulnerable to mould owing to unseasonable rains and dew.
Generally, the donkey weed is harvested by grazing. Nonetheless, this herb can also be harvested as a green feed. On the other hand, it can be harvested like a hay crop and used to feed animals, especially in the dry months. This plant is nutritious for animals and can be fed to animals as a protein supplement.