Delphinium species: Larkspur

Family

Ranunculaceae

Common Name

Larkspur, delphinium

Plant Description

The genus Delphinium consists of some 250 species native to the Northern Hemisphere, with only a few species found in Africa. Numerous cultivars and hybrids have been developed as popular ornamentals. There are 61 species of Delphinium native to North America [1]. Delphiniums are annual or perennial herbs developing from a woody root or rhizome. Stems are erect and hollow. Leaves are simple, alternate, basal, the basal leaves generally being larger than the leaves higher on stems. The blades are deeply palmately divided into 3 - 7 major lobes, each lobe being further divided.

Inflorescences of terminal racemes or occasionally panicles. Flowers are perfect, bilaterally symmetrical, with 5 sepals, 4 petals with the two upper forming a characteristics spur (Fig. 139, Fig. 140 and Fig. 141). Nectaries are present in the spur. Fruits of follicles with curved beaks and numerous dark brown seeds.

The annual larkspurs are now placed in the genus Consolida. The showy garden Delphiniums have been mainly derived from Delphinium elatum, and not the more toxic native species such as Delphinium barbeyi, D. californicum, D. glaucescens, D. geyeri, and D. nuttallianum. It is of interest to note that larkspur poisoning causes more cattle deaths in the Rocky Mountain region than any other genus of plants [2,3].

Figure 139. Delphinium elatum hybrid.

Figure 140. Delphinium elatum hybrid flowers.

Figure 141. Delphinium virescens flower.

Toxic Principle and Mechanism of Action

Delphinium species contain a large number of diterpenoid alkaloids, with some of the more toxic species such as Delphinium nuttallianumcontaining some 27 alkaloids [4-8]. The 19-C diterpene alkaloids including methyllycaconitine, nudicauline, and 14-deactylnudicauline have been shown to have the greatest toxicity in animals. These alkaloids have a curare-like, competitive, non depolarizing, neuromuscular blocking effect by inhibiting acetylcholine at the nicotinic postsynaptic receptor sites [5]. The levels of alkaloid vary considerably with the species and the stage maturity of the plant. The preflowering plant has the highest concentration of alkaloids [10,11].

Cattle are the most susceptible to the toxic effects of the alkaloids, while sheep are quite resistant. Horses are susceptible to poisoning, but rarely eat the plants. Mice are quite susceptible to poisoning and are a good experimental model species [12].

Risk Assessment

Larkspurs are commonly grown as colorful garden perennials, but are unlikely to be poisonous to household pets. However, because of their potential for poisoning livestock species, care should be taken in disposing of the plants from the garden.

Clinical Signs

The neuromuscular blocking effect of the toxic Delphinium species develops three to four hours after the ingestion of the plant. Initially, muscle tremors, weakness, and an inability to stand are common. Lateral recumbency, bloating, and death occur if a lethal dose of the alkaloids is consumed.

Physostigmine at a dose of 0.04 - 0.08 mg per kilogram body weight given inter peritoneally is the most effective means of reversing the neuromuscular blockade (intravenous administration should be done very cautiously). In cattle it is important to keep the animals in sternal recumbency to avoid bloat.