These vegetables (and Kohlrabi, and Collard Greens, and Gai Lan, and Bok Choy, and Red Cabbage) may be familiar in the kitchen, but they do not exist anywhere in nature—and they are all the same species of plant.
"Hidden History" is a diary series that explores forgotten and little-known areas of history.
Kale, Brussels Sprouts, Broccoli, and Cauliflower---all from the same species of plant
The Brassica is a very large and diverse family of plants, with some 4,000 species in 372 genera found on every continent except Antarctica. It used to be known as “crucifers”, from the four-petaled flowers found on many of the species, but that name is now obsolete, and the family is now usually referred to as “mustards”. It contains such familiar plants as the Radish, the Turnip, the Arugula, the Horseradish, the Rutabaga, the Wasabi, the Watercress, the Mustard (from which we get greens and the condiment), the Rapeseed (from which we get Canola Oil), and the Woad (from which we get a blue dye for cloth). The name “Brassica” comes from the Latin word for “cabbage”.
The entire Brassica family is prone to a strange biological phenomenon known as “polyploidy”. Normally, living organisms have two of each chromosome in their cells, one from their mother and one from their father. When a plant or animal produces pollen/sperm and ova/eggs, these chromosomes are copied to form a new set, and then this pair will split to form reproductive gametes which each contains just one member of the pair (a process known as “meiosis”). When mating occurs, these single chromosomes join together to form new pairs in the cells of the offspring.
Occasionally, however, this process goes awry, and for some reason the chromosomes fail to separate. This leads to gamete cells that have two or more sets of chromosomes, which then combine with another pollen or ovum during mating to produce cells with extra copies of the chromosomes, a condition known as “polyploidy”. In some instances, these “polyploid” individuals can survive and reproduce, and this extra genetic material then provides a rich source of new genetic variations, since altering the genes in these extra chromosomes does not interfere with the normal copy. In many members of the Brassica family, this polyploid process has happened several times during their evolutionary history, producing plants that have as many as 17 sets of chromosomes instead of the usual two.
And this genetic diversity would lead to one of the most common and important of the food plants used by humans, one which seems to make up most of the Fresh Produce section in the store. Every part of the plant, from the root to the stem to the lateral buds to the terminal leaf buds to the flowers to the seeds, has been altered by centuries of artificial selection and directed breeding to serve a human purpose.
The wild form of the Cabbage plant, Brassica oleracea, is not very impressive: it is a small weedy-looking thing with curly leaves, thick stems, and small four-petaled yellow flowers, which grows on steep rocky seashore cliffs where not much else can compete with it. Although the species has now been spread by humans all over the world, its original range was probably in the cooler areas of Spain, France, and the British Isles in western Europe, where it preferred well-drained alkaline soils and would store water and minerals in its thick leaves. The plant apparently spread out from there around the rim of the Mediterranean Sea.
The oleracea plant is a triploid—that is, it has three copies of each chromosome in its cells instead of the usual two. Analysis indicates that this configuration appeared about 4 million years ago. The diversity is striking: about 20% of all the known B. oleracea genes are only found in a handful of the many various cultivars, and some varieties have entire genes that are not found in any of the others, even though they are all the same species.
We do not know when the Brassica oleracea plant was first domesticated. Genetic analysis indicates that it may have been around four thousand years ago, but the complicated and convoluted genetics of this plant make any such conclusion tentative at best. It most likely, however, happened in the eastern Mediterranean around Turkey and the Levant, which was near one of the areas in which humans first began intentionally cultivating food plants. The exact ancestry of the domesticated Brassica is still debated, with a few arguing for a single point of origin in Asia Minor and most others arguing for multiple independent origins in Europe, Asia Minor and/or China. There are also indications that domesticated Brassica had many times escaped cultivation and became feral in the wild, only to later be domesticated again.
By the 6th century BCE, the Greeks were producing Brassica as a garden plant for their cooked edible leaves, which they referred to as rhaphanos. In addition to the wild-type plant, there was a curly-leaf agricultural version and a smooth-leaf. These would have been prepared in a way similar to Spinach and would likely have had a slightly bitter taste—something like modern Mustard greens. By the time of the Romans, careful selection of cultivated plants had produced a version of Brassica with a larger curly-edged leaf, which was the ancestor of today’s Kale and, sometime later, of Collard Greens.
The Romans also had a preference for plants which produced tight bundles of packed leaves, which could probably be more easily harvested, and “Cabbage heads” seem to have appeared around the first century CE, though they were smaller than ours. The Romans had several varieties, and ancient writings tell us that the famed Senator Cato liked his Cabbage, either raw or cooked, in vinegar, while the aristocratic Lucullus thought the plant was plebian and beneath the dignity of Roman patricians. Cabbage also had uses in Greek and Roman herbal medicine, being prepared in various ways to treat headache, gout, and mushroom poisoning.
These table vegetables became popular and quickly spread throughout the Empire and its surroundings. As “Cabbage” was appearing among the Romans, moreover, the Germanic tribes in cooler and wetter northern Europe were already producing a new variety of Brassica that had smaller leaves and thicker stems with a large bulblike growth at its base, which could be better grown here than in the warmer Mediterranean climate. This new variety was the ancestor of our modern Kohlrabi.
After the collapse of the Roman Empire, the Brassica remained popular in Europe, and new varieties continued to be selectively bred. The large Cabbage heads of the type we see today appear in around the 10th century CE. (The name “Cabbage” comes from medieval times, and is derived from an Old French word for “head”.) They were useful as foods for sailors, who could store them in the cool dark holds of a ship as a vital source of vitamins to prevent scurvy and other deficiency diseases on long sea voyages. Particularly suited for this purpose was sauerkraut, which consisted of sliced Cabbage cured in vinegar. A 13th century French cookbook advises the chef to make fresh soup for the table: "Take cabbages and quarter them, and seethe them in good broth".
By the 15th century, people in southern Italy and Sicily had begun breeding plants that produced many bundles of flowerheads with thousands of tiny immature flowerbuds that never opened. One of these varieties produced large green flowerheads and became “Broccoli”, while another variety was selected to form undeveloped white flowerbud tissue instead of maturing green buds, and this became “Cauliflower”. It is probable that one of these is ancestral to the other, but we do not know which is which, or exactly when it happened (though there are some genetic hints that the Broccoli came first).
In northern Europe, however, Brassica were selected for cold tolerance, and plants that produced many small tightly-packed lateral leafbuds (looking sort of like miniature Cabbages) were favored. These first appeared in the early 18th century in Belgium, and became known as “Brussels Sprouts”. (Though there are some claims that these had appeared as early as the 12th century.)
While all of this was going on in Europe, moreover, the vegetable had been spread to India by Portuguese traders (although it already grew there and had already been mentioned in Sanskrit texts from 1500 BCE), and the native Chinese plant Brassica rapa (whose natural range extended into Europe and had already produced the Turnip there) had also been adopted as a food plant in the Far East. New varieties were bred in China that were well-suited for the Asian climate and the local cooking methods. These are now known as Bok Choy and Gai Lan. In Korea, Cabbage soaked in vinegar is a key element of kimchi.
Today, the hunt for new varieties continues, but this is most often accomplished now by means of hybridization, in which a Brassica oleracea cultivar is artificially crossbred with other varieties and sometimes with other species from the same genus, especially B. juncea (the Mustard plant) and B. rapa (the Chinese Cabbage), or even from a different genus such as the Raphanus Radishes. This process has led to several new vegetables which did not exist before, including Broccolini, Kalette, Brassicoraphanus, and Broccoflower.
There are also a number of ornamental varieties of Cabbage and Kale now available, which do not produce the typical round Cabbage heads but instead form colorful and decorative crinkled leaves which are intended to be looked at, not eaten.
NOTE: As some of you already know, all of my diaries here are draft chapters for a number of books I am working on. So I welcome any corrections you may have, whether it's typos or places that are unclear or factual errors. I think of y'all as my pre-publication editors and proofreaders. ;)
