The balsam pear, Momordica charantia (not at all related to the familiar pear we buy in North American markets), is an annual vine native to the Old World Tropics, but widely escaped and naturalized in warm regions of the world, including the southeastern United States coastal plain west to Texas. A very similar species M. balsamina, is seldom seen in the wild in the United States, although it is occasionally cultivated. M. charantia grows rapidly from seeds, climbs by way of spirally-coiled tendrils, soon draping vegetation, fences and other upright structures. After only a few months it produces small yellow, unisexual flowers on the ends of long stalks. The female flowers, if fertilized, are followed by fleshy, tuberculate (i.e., fruit exterior is ornamented with bumps and ridges) fruits, at first green, then becoming bright orange. The fruits may be as much as 4” (10 cm) long, but usually are smaller, at least in the United States. When ripe, the fruit splits open, revealing its seeds linearly arranged along the edges of the three fruit segments, each tan-colored seed embedded in a fleshy,
soft red aril (further discussed below).
Botanically similar or identical to the balsam pear is the “bitter melon” or “bitter gourd” of Asian cuisine. It also is classified as Momordica charantia but its fruits (the only part of the plant ordinarily to be seen outside of its native habitat) differ markedly from those of the balsam pear. They are much larger, some approaching a foot in length. Widely available in Chinese, Indian, and other speciality markets, the bitter melon is consumed by humans but only in the green, immature state. If allowed to ripen, the bitter melon like the balsam pear, becomes toxic to humans and to small animals. Severe diarrhea and vomiting are reported to occur in humans who eat the ripe fruit and seeds of M. charantia. The ripe fruits in small amounts also have been used to induce abortion.
The large size of the bitter melon may be the result of artificial selection, the term used by Charles Darwin to describe the preference of humans for certain traits when conducting plant and animal breeding. Artificial selection, continued over long time periods can lead to genetic change within species of plants and animals that fixes traits desired by humans. Continuing selective breeding over many generations can produce offspring very different from their ancestors, and commonly, but not universally, varieties selected artificially lose their ability to survive without human help. Breeds of dogs (compare wolves, Great Danes and Chihuahuas!) and cattle, as well as corn, tomatoes and other fruits are examples. It’s not surprising, then, that the bitter melon is not reported as growing wild as is the balsam pear. However, I am unaware of any data that would clarify the genetic differences between the wild and the domesticated M. charantia.
The photo shows half a bitter melon, 12 cm in length sliced in cross-section, then along its length. The left piece shows the exterior.
The aforementioned aril is a fleshy appendage to the seed that usually envelops the seed and is brightly colored. It is not part of the seed but usually originates from the stalk to which the seed is connected. Animals are attracted to arils and often eat the enclosed seeds and in some cases the aril as well. It thus seems likely that the aril serves as an adaptation selected to increase the effectiveness of seed dispersal. I have repeatedly observed Northern Cardinals pluck aril-covered seeds from opened M. charantia fruits and then carefully strip off the aril with their beaks and consume the seeds. Only a few plants produce arils. Other species with arils include the yew (Taxus canadensis of North America, and a related species in Europe)- a conifer in which the cone is reduced to a single seed surrounded by a modified scale that becomes a soft, red aril edible by humans. The seed (and other parts) of the yew are poisonous to humans but the seed is consumed and dispersed by birds. The aril of the nutmeg seed which is ground up for spice is called mace. The pomegranate not only produces an edible aril but this juicy covering is the part of the plant sought by humans although the seed also is edible.