Crotalaria

Several species of Crotalaria are cultivated as crops to be consumed by human populations throughout the world. To ensure the survival and optimal cultivation of these plants, they are often selected for resistance to diseases, yield, and nutritional quality.[5]

The wild and domesticated landraces of Crotalaria tetragona, colloquially known as “Tum-thang,” are grown and eaten by the tribal communities of the Mizoram state of North-east India. The flowers and pods of Crotalaria tetragona are eaten as vegetables, the flowers and buds are used as garnishing, and the seeds are eaten as pulse.[6] In the Lake Victoria basin of East Africa, the wild and cultivated lines of Crotalaria brevidens, also known as “mitoo,” are harvested and eaten as a leafy vegetable in many popular cuisines. Its wide consumption is mainly due to its nutritional value as a rich source of β-carotene, which is a precursor of vitamin A.[7] Crotalaria longirostrata, also known as longbeak rattlebox or chipilín, is found in Guatemala, El Salvador, and Oaxaca and is a popular addition to many local dishes. The edible portions of the plant are the leaves and shoots, which are cooked and served as a leafy green vegetable or desiccated and used as an herb. The foliage contains high amounts of calcium, iron, thiamine, riboflavin, niacin, and ascorbic acid, while the seeds and roots are considerably toxic.[8] Crotalaria longirostrata is considered a noxious weed in the United States since it is avoided as a source of consumption by many animals and since its seeds shatter and spread over a wide range.

Australian species of the genus Crotalaria have the capacity to be cultivated into potential grain crops that are adapted to dry environments, nutrient poor soils, and low-input agricultural systems. Australian Crotalaria species also show many suitable traits of harvestability, including an upright growth habit, a low tendency to dehisce and shatter, the bearing of its fruits and flowers at the ends of branches, and large to moderate seeds.[9]

Several species of Crotalaria are currently being cultivated for suitable traits that are not directly related to human consumption. Crotalaria juncea, also known as sunn hemp, is currently grown throughout the tropics and subtropics[10] as a source of green manure, lightened fiber, and fodder. Crotalaria juncea is also being considered as a potential source of cellulosic ethanol for biofuel.[11]

To analyze the differences in crop yield of Crotalaria in different regions, samples of Crotalaria brevidens and Crotalaria ochroleuca were taken from each setting and analyzed for crop yield under different water supply conditions. The results of the study show that Crotalaria plant height was extremely sensitive to water supply, and significantly led to a decrease in the shoot heights and leaf sizes in these two species, which ultimately meant lower crop yield. As a result, it can be said that Crotalaria was proven to grow better in regions with more adequate water supplies (ex.- they are predicted to grow better in swamplands than in deciduous bush land).[12]

The primary source of toxicity for many species of Crotalaria is the presence of pyrrolizidine alkaloids, which are poisonous to birds and large mammals. The two kinds of pyrrolizidine alkaloids that are found in Crotalaria plants are monocrotaline and spectabiline. Monocrotaline is most toxic to the pulmonary vasculature and is used in animal studies to induce pulmonary arterial hypertension for human modeling. Both alkaloids show clinical hepatotoxicity and carcinogenicity. They can be found in the leguminous seeds, foliage, stems, or roots of Crotalaria plants. Species with higher concentrations of pyrrolizidine alkaloids yield greater toxic effects compared to those with lower concentrations. In addition, species that contain only monocrotaline are more poisonous than species that contain only spectabiline at equal concentrations within the seeds, leaves, stems, or roots. There are no confirmed species to this date that contain both spectabiline and monocrotaline; a Crotalaria plant can only have either one or the other. Thus, plants that are less toxic and therefore more appropriate for human consumption carry only low concentrations of spectabiline. According to one study, species that display the greatest toxicity include Crotalaria spectabilis Roth, C. retusa L., C. alata Leveille, and C. quinquefolia L. Species that are least toxic include Crotalaria australis Bak. Ex Verdoorn, C. maxillaris Klotzsch, C. sphaerocarpa, C. juncea L, and C. brevidens Benth., among many others.[13]

Danaiine butterflies on Crotalaria (Kerala, India)

The toxic alkaloids are attractive to butterflies in the subfamily Danaiinae and large aggregations of butterflies occur during the flowering of Crotalaria species in Asia. These butterflies also obtain alkaloids from sap emerging from withering stems and terminal branches.[14][15]

Among pyrrolizidine alkaloid-containging plants, Crotalaria species cause the greatest range of tissue damage to most domesticated species, causing lung lesions in cattle, sheep, goats, horses, and pigs, and liver damage in most livestock.[3] Some species produce severe kidney lesions[3]

In March 2019, horses in the Federal District of Brazil were fed oats contaminated with Crotalaria seeds, from an earlier seeding intended to increase nitrogen levels in the soil, and at least 13 of them died of liver failure.[16]