Pieris species: Pieris

Family

Ericaceae (Heath family)

Common Names

Japanese pieris, mountain pieris, mountain fetterbush, lily of the valley bush.

Plant Description

The 10 species of Pieris are native to the acidic, moist soils of the temperate regions of North America and eastern Asia. As small to large, erect, branching shrubs, leaves are ovate to lanceolate, alternate, glossy, reddish-bronze initially in the spring, turning dark green in maturity. Inflorescences are terminal panicles or racemes. The fragrant flowers are showy, white to dark pink, cylindrical or bell-shaped, pendent, with 5 fused sepals and 5 fused petals. Fruits are ovoid capsules (Fig. 314 and Fig. 315).

The species of Pieris most frequently associated with toxicity include Pieris japonicus (Japanese pieris) and P. floribunda (mountain pieris). Numerous cultivars exist, and are popular for their new foliage color and prolific flower production in the Spring.

Figure 314. Pieris japonica flowers.

Figure 315. Pieris japonica "pink".

Toxic Principle and Mechanism of Action

All species of the family Ericaceae contain varying quantities of toxic diterpenoids collectively known as grayanotoxins I and II (formerly andromedotoxin, rhodotoxin, and acetylandromedol) [1]. As many as 18 grayanotoxins (I – XVIII) have been identified, the greatest number being found in the Leucothoe species (fetter bush) [2,3]. Tannins and other compounds are also present in varying amounts. All parts of the laurel including the flowers are toxic, although there may be considerable variation between species.

Grayanotoxins act to increase sodium channel permeability of cells by opening the channels to sodium, which enters the cells in exchange for calcium ions, thus rendering the channels slow to close so that the cell remains depolarized [4,5]. Other neurologic mechanisms may also involve a cholinergic response seen clinically as bradycardia and excessive salivation [6]. The cardiac effects can range from bradycardia, sinus arrest, and arrhythmias.

Other members of the Ericaceae that contain grayanotoxins include:

Andromeda polifolia                 Andromeda, bog rosemary

Kalmia spp.                                Laurel

Ledum spp.                                Labrador tea

Leucothoe spp.                          Fetter bush, dog laurel

Lyonia spp.                                 Maleberry

Menziesia spp.                           Rusty menziesia

Rhododendon spp.                   Rhododendrons, azaleas

Risk Assessment

Pieris species are commonly grown as showy garden shrubs. Livestock poisoning occurs where the plants are accessible to the animals.

Clinical Signs

Excessive salivation, increased nasal secretions, vomiting, abdominal pain, bloat, and irregular respirations develop several hours after Pieris leaves are ingested [8,9]. Projectile vomiting may be noticeable. Hypotension, tachycardia, and respiratory depression may also develop. Weakness, partial blindness, and seizures have been reported in severe intoxications. Neurologic signs may persist for several days before the animal recovers. Weight loss may be notable. Death may result from the inhalation of vomited rumen contents [10]. Pregnant goats eating Pieris can cause fetal mummification [11].

Treatment is primarily directed at relief of the more severe clinical signs. Activated charcoal given orally is helpful if given shortly after the Pieris is consumed. Atropine is useful in countering the cardiovascular effects.