When I was a kid we had banks of yellow flowers growing in the area where my parents had hired a contractor to re-grade the property. The topsoil had been scraped away and they did not purchase new soil to cover the raw mineral subsoil that was now the top layer of the landscape. Consequently the area was invaded by hardy exotic species that were adapted to environmental disturbance.
As little kids will, we loved the little yellow flowers with elaborate geometry that looked like a dragon’s head that you could squeeze at the base to make its “mouth” open. We called them “snapdragons,” although I don’t know where we had heard that name. My mother corrected us, saying they were in fact called “butter and eggs.”
Linaria vulgaris has dozens of vernacular names, only one of which – wild snapdragon – references its resemblance to Antirrhinum majus, the actual snapdragon. Until recently both of them were classified as members of the Scrophulariaceae family, but Antirrhinum, on the strength of molecular genetic evidence, has been reassigned to Plantaginaceae or the plantain family.
Many of the common names of Linaria refer to the animal-like appearance of the blossom: bunny haycocks, bunny mouths, calf’s snout, impudent lawyer (!), lion’s mouth, monkey flower, and rabbit flower. By comparison snapdragons have far fewer names in the folk lexicon. This is likely because of the tendency of Linaria to rapidly colonize disturbed landscapes and so be much more often encountered by working lay people. Antirrhinum, in contrast, likes deep, well-drained, fertile soil, and so is less likely to spread across the landscape unchecked.
Unlike Linaria, Antirrhinum has been cultivated and many varieties produced through careful breeding. Snapdragons are common addition to many perennial gardens because their vertical growth habit adds interest to the texture of a bed and many of the colors in the cultivars tend toward strikingly saturated reds and magentas.
The zygomorphic (bilaterally symmetrical) flowers are arranged in spirals up a tall stalk that varies in height from 10 inches to two feet. The blossoms open successively from the bottom to the top of the spike. The flowers of the cultivars come in a wide variety of colors, most of which are hot and bright.
The form of the flower, which was apparently evolved independently in Linaria and Antirrhinum, is an adaptation to effective pollination by bees. When a bumblebee lands on the flower its weight opens the “mouth” and it crawls in. The corona closes around it and the bee is thoroughly coated with pollen before moving onto the next flower, where it transfers the pollen to stigma.
Wild snapdragons and earlier cultivars were not particularly valued as cut flowers because after they were fertilized the blossomed fell off (“shattered”). Careful cross breeding, however, has produced “shatter-proof” varieties.
Snapdragons are perennials, but they are often planted as annuals, especially in colder climates. The plants can be put in the ground after the threat of frost is past and they will begin blooming in early June in the northern United States. By the heat of mid-summer the flowers will have fallen off. At this point most gardeners recommend cutting them back to about 6 inches above the ground, fertilizing and watering them heavily. They will produce a second wave of flowers through the fall and continue to bloom even after a frost.
Antirrhinum majus is found in the wild in the Mediterranean region, ranging from Portugal and Morocco to Turkey and Syria. It tolerates colder climates, however, and has escaped from cultivation in both Europe and North America to establish wild populations locally.
Like Mendel’s peas, Antirrhinum demonstrates incomplete dominance. That is, a white variety crossed with a red variety will yield a pink-flowered crop. Charles Darwin was intrigued that the normally zygomorphic flowers of snapdragons were occasionally replaced with actinomorphic (radially symmetrical) flowers, a condition known as “peloria.” Subsequent molecular research revealed that a single gene called “CYCLOIDEA” controlled floral symmetry in some plants, including snapdragons. Breeders have exploited these and other characters to produce an astounding array of cultivars.