Senecio species: Senecio, cineraria

Family

Asteraceae

(Packera species)

Common Names

Cineraria                     Senecio cruentus (Pericallis)

Dusty miller                S. cineraria (S. bicolor)

String of beads          S. rowleyanus

Natal ivy, wax vine     S. macroglossus

Many species of Senecio are now considered in the genus Packera. Although most of the species are wildflowers, some are noxious weeds and are a perennial source of poisoning to animals that eat them. A few species have become popular house and garden plants because of their showy flowers or succulent leaves.

Plant Description

This large and varied genus of over 3000 species is worldwide in distribution. Senecio species are either annual, biennial, or perennial forbes, shrubs, climbers, or succulents. Leaves are alternate, varying considerably in shape, being entire or serrated, lobed or pinnately dissected. Flowers are numerous, produced terminally, daisy-like, usually yellow, but can also be white, blue, orange, or red in color (Fig. 360, Fig. 361 and Fig. 362). Seeds are cylindrical achenes with a hairy pappus that aids in wind distribution.

Figure 360. Senecio jacobaea (tansy ragwort).

Figure 361. Senecio cruentus (Pericallis).

Figure 362. Senecio rowleyanus.

Toxic Principle and Mechanism of Action

Not all species of Senecio are poisonous, but those that are contain toxic pyrrolizidine alkaloids (PA) [1,2]. These alkaloids are converted by the liver into toxic pyrroles that inhibit cellular protein synthesis and cell mitosis [3-5]. Hepatocyte necrosis, degeneration, and liver fibrosis with biliary hyperplasia characterize the toxic effects of the pyrrolizidine alkaloids. There is considerable variation in the toxicity of the alkaloids depending upon the species. Horses and cattle are susceptible to PA poisoning, while sheep and goats have rumen microflora that readily transform the PA into non toxic metabolites [6].

Pyrrolizidine alkaloids are also abundant in the genera Boraginaceae, and Fabaceae. Some of the common species in these genera that contain toxic PAs include Amsinckia (Fiddle neck), Crotolaria (rattle box), Echium (vipers bugloss, blue weed), Cynoglossum officinale (hounds tongue), Symphytum species (comfrey), and Heliotropium (heliotrope) [3,7].

Risk Assessment

The Senecio species that are most frequently grown as garden or house plants do not generally contain significant quantities of the toxic pyrrolizidine alkaloids. Furthermore, it is unlikely household pets would ingest sufficient quantities of the plant to induce liver toxicity. Herbal products containing comfrey should be used very cautiously because comfrey does contain toxic PA.

Clinical Signs

Animals that consume PA containing plants over a period of time develop signs related to liver failure. Horses and cattle are generally the most severely affected, while sheep and goats are quite resistant to PA toxicity. Weight loss, icterus, diarrhea, photosensitization, and neurologic signs related to hepatic encephalopathy are typical of liver failure. Serum liver enzymes are generally elevated significantly.

Confirmation of PA toxicity can be made by a liver a biopsy showing the triad of histologic changes characteristic of PA poisoning, namely liver megalocytosis, fibrosis, and biliary hyperplasia.

Treatment of animals with PA poisoning is generally limited to placing the animal in a barn out of the sun to relieve the photosensitization, providing a high quality, low protein diet, and removing all sources of the PA from the animal’s food. The prognosis is generally very poor as once clinical signs of liver failure from PA poisoning occur, the degree of liver damage is severe and irreversible.