Kalanchoe is a genus of 150 to 200 plant species, most of which are native to southern Africa, Madagascar, and Australia. In the past,
the genus was divided into three genera: Kalanchoe, Bryophyllum, and Kitchingia. But today most botanists recognize it as one genus.1 In the United States, Kalanchoe species are primarily ornamentals and houseplants, but some have escaped cultivation and can be found in the wild, especially
in Florida and Hawaii. Table 1 lists the most common Kalanchoe species found in North America.
Table 1 Common Kalanchoe Species Found in North America.
Although the plants vary, most Kalanchoe species are erect, growing shrubs (Figure 1). These perennial plants generally have thick, green, succulent foliage and clusters of small flowers (Figures 2 & 3). The plants are popular with florists because they can be forced to bloom at any time of the year, including holidays. Kalanchoe species' flowers can be many colors, but red, yellow, pink, orange, and white are the most common. The plants' bloom time
is long; flower clusters can last for weeks to months. Most Kalanchoe species are easy to propagate from leaf or stem cuttings. Many species have plantlets (miniature plants at the end of flowering
stems) growing in the notches of the leaf margins; these plantlets are so prolific that they sometimes escape into the wild.
Figure1. A Kalanchoe species shrub. Notice the thick green leaves and the small clusters of red flowers.
Kalanchoe species contain cardiac glycosides and are toxic to animals. In South Africa and Australia, where these plants are found
in the wild, cattle and sheep poisonings are common.2-4 Toxicosis occurs primarily in the summer months because the flowers contain a much higher concentration of glycosides than
the stems, leaves, or roots do.2 Although the toxic dose of Kalanchoe species in small animals is unknown, in calves the lethal dose is estimated to be 7 g of flowers/kg body weight or 40 g of
leaves/kg body weight.2,3 In the United States, Kalanchoe species represent little risk to livestock because the plants are not commonly found in pastures. However, household pets,
including dogs, cats, and birds, are susceptible because the plants are used in landscaping and kept as houseplants.
Figure 2. The flowers of the Kalanchoe blossfeldiana plant, the most common ornamental Kalanchoe species in the United States.
Mechanism of action
Kalanchoe species' toxicity is primarily due to a group of bufadienolide compounds, including bryotoxins, bryophyllins, and bersalgenins.1,5 Bufadienolides are cardiac glycosides that are similar to digitalis compounds. Inhibition of the cellular membrane sodium-potassium
pump (Na+,K+-ATPase enzyme system) produces the cardiotoxic effects. In the heart, this system pumps sodium out of the cell
in exchange for potassium. When the pump is inhibited, intracellular sodium concentrations begin to increase, and potassium
concentrations decrease. The increased intracellular sodium can be exchanged through the sodium-calcium exchanger for calcium,
which improves contractility. Because of this effect, these glycosides (e.g. digoxin) can be used pharmacologically as positive inotropes to increase myocardial contractility. However, these changes
in ion flux can cause a progressive decrease in electrical conductivity through the heart, resulting in irregular heart activity
and, eventually, termination of cardiac activity. In toxic doses, cardiac glycosides increase sympathetic discharge to the
heart and automatic rhythmicity, thereby potentiating ventricular arrhythmias.
In summary, bufadienolides inhibit the sodium-potassium pump of the myocardial cell membrane, leading to frequent and irregular
depolarization of the cell. This results in disorganized cardiac electrical activity, manifesting in a variety of arrhythmias
and eventually leading to cardiac arrest.
Figure 3. Kalanchoe species plants (white flowers) in an ornamental garden with tulips (red flowers).