PLANT OF THE WEEK
Dr. T. Ombrello - UCC Biology Department
Dumbcane, Mother-in-Law’s Tongue, Dumb Plant
Scientific name: Dieffenbachia picta
of scientific name:
- Name commemorating J.F. Dieffenbach (1794-1847), a German physician and
Latin for painted or variegated in reference to the interesting color patterns
on the leaves.
With common names like
Mother-in-Law’s Tongue and Dumbcane, you can be sure that this plant has an
interesting story associated with it. A
popular houseplant for over 150 years, the Dumbcane is native to South America
where it is commonly found growing in tropical jungles, especially in Brazil.
As members of the Arum family of plants
(Araceae), all 30 members of the genus Diffenbachia, including
the Dumbcane, count as close relatives such well-known plants as Philodendron,
Pothos, Calla, Anthurium, Spathiphyllum, and Skunk Cabbage.
The relationship between Dumbcane and Skunk Cabbage becomes very obvious
when either plant is bruised. They
both emit a skunk-like odor.
The Dumbcane, like all
Arums, has an interesting blossom that consists of many small, inconspicuous
flowers densely packed on a stalk called a “spadix”.
The spadix is surrounded by a showy “spathe”, which is a modified
leaf or bract. Dumbcane can get
quite tall. Their rarely branching
stems look like canes and can reach heights of over 10 feet.
As they increase in size it is quite natural for their large green,
white, and yellow-blotched leaves to be lost from the lower portions of the
plant, leaving just exposed canes.
Undoubtedly the most
intriguing characteristic of the Dumbcane relates to its common names.
It has been known for over a century that the plant contains crystals of
calcium oxalate, and if any part of it is eaten a sudden burning irritation and
paralysis of the mouth, tongue, and lips will result.
This usually prevents a person from talking for a while, which has led to
the amusing common names. The
ingestion of this plant, however, can have some serious consequences such as
vomiting, diarrhea, and intense salivation.
Death has been reported to occur when tissues at the back of the tongue
and throat swell and block air passage.
In 1963 it was
discovered that specialized cells called idioblasts within the Dumbcane could
“shoot” double-pointed, sharp, needle-like crystals of calcium oxalate much
like darts from a microscopic blowgun. These crystals, called raphides, are forcibly ejected from
the idioblasts after the tips of these cells are broken off as a result of
tissue damage such as from chewing. These
crystals readily penetrate the soft tissues all along the digestive tract of an
animal. With the aid of an electron
microscope, the presence of barbs along the length of the raphides has been
demonstrated. They probably prevent
the raphides from being readily dislodged from the soft animal tissues once
penetration has occurred. The only
effective way to rid the mouth of the crystals other than letting nature take
its course is to rinse the mouth with vinegar to dissolve the imbedded crystals.
The rinse should not be swallowed. The
raphides also have 2 grooves running down their sides, making it possible for a
proteolytic enzyme in Dumbcane to penetrate the mouth and throat tissues.
The enzyme is very similar to those found in scorpion and snake venoms,
and accounts at least in part for the localized paralysis suffered by animals
ingesting this plant.
As bad as all this
sounds, it is fortunate that the raphides remain largely undissolved during
their passage through the digestive tract.
If these crystals of calcium oxalate were to dissolve internally, the
resulting oxalic acid would create an imbalance of blood minerals and a plugging
of kidney tubules with often fatal results.
The adaptive value of
the idioblasts and their raphides to the Dumbcane is twofold.
The plant “disposes” of potentially toxic excess oxalic acid that
accumulates in the plant’s tissues by forming insoluble calcium oxalate
crystals (raphides). These crystals
protect the plant from herbivores (plant eating animals).
No animal will have a second helping of Dumbcane.
Through hybridization and natural mutation, many fancy-leaved Dumbcanes have been developed and released into the nursery trade. As a result, there are a number of cultivated varieties with all sorts of leaf color patterns. One of the more famous is ‘Rudolph Roehrs’, developed in New Jersey from a striking chartreuse, ivory, and green-leaved mutant in 1937.
A Dumbcane plant growing in one of Union County College's greenhouses.
|A 'Rudolph Roehrs' cultivar of Dumbcane, growing in one of Union County College's greenhouses.|