Dandelions – Background

Even the smallest child recognizes the common yellow dandelion. Their sunny flowers, bundled and offered as bouquets, announce that spring is here. Whether they bring a smile or a frown, you can’t help but admire a plant that seems to be able to grow anywhere – from lawn to roadside, from parking lot to playground. Dandelion flowers serve the same function as all other flowers: to produce seeds for the next generation. Though not native to North America, dandelions are here to stay, thanks to a whole host of strategies that ensure their fluffy seeds will float on breezes far and wide.

The dandelion, or Taraxacum officinale, gets its common name from the French dents de lion or teeth of the lion, thought to describe its jagged leaves. These toothed leaves are one of the dandelion’s many secrets to success. They grow in a circle or rosette at ground level and form a tight cluster at the base of the plant. They effectively stake their claim to space and block out sunlight, shading out any competing plants. The closer they’re clipped, the lower they grow, a trait that helps them avoid the blades of lawnmowers and teeth of grazing animals. Each leaf is grooved lengthwise along the midrib, which helps channel water to its root crown and growth center. Despite similar growth habit, there can be great variation in leaf length, width, tooth size, and shape.

Dandelions have a thick, unbranched taproot that can grow to a depth of eighteen inches. This root gathers up water and nutrients from the soil and secures the plant in many a challenging location, from cracks in a sidewalk to the edge of a flower bed. Its root hairs spread out and help anchor the dandelion firmly in the soil, making it difficult to uproot and eradicate, especially because even the smallest piece left behind can grow into a new plant. The root also functions as a nutrient storage center, providing energy for new growth if the plant is grazed or mowed.

Dandelion flower buds can be found growing from the center of the root crown. They are tucked in among the leaves, and their hollow stalks elongate when they begin to flower. Though it may look like one sunny yellow flower, a dandelion is actually composed of many individual flowers or florets, packed together to form the blossom or flower head. To understand a dandelion, it’s best to start by learning the parts of a simple flower like a lily or tulip. At the flower’s base is a ring of sepals, leaf-like structures that protect the bud. Next comes a ring of colorful petals for attracting pollinators. Inside the petals are the stamens, the pollen-bearing (male) parts, made up of a stalk (filament) tipped with a capsule called the anther, in which the pollen develops. The innermost part of the flower is the vase-shaped pistil, the seed-bearing (female) structure. At its tip is the stigma, sticky or feathery to catch pollen, supported by a stalk (the style) and, at its base, the ovary containing the ovules, tiny eggs that, when fertilized by pollen, become the seeds.

A single dandelion flower head can be made up of hundreds of these tightly packed, overlapping florets, set in a cup-shaped receptacle. Each floret is a complete flower with the same floral parts as a simple flower but modified and in miniature. It has a strap-shaped petal with five tiny teeth at its tip and lines running its length, evidence of the evolutionary fusion of five petals. The base of the petal forms a tube containing nectar. Below the petal lies the ovary, which when fertilized will grow into a fruit with a single seed. Between the ovary and the petal are modified sepals, resembling a tuft of white hairs, called the pappus. They help to disperse the dandelion seed by becoming the parachute that carries the seed on the wind. Emerging from each floret is the style. As the individual flowers mature, a forked stigma at the tip of the style unfurls into drooping curlicues. The anthers are fused into a thickened pollen tube, which encircles the style. The anthers are full of pollen, and when ripe they shower the floret with pollen grains. These flower heads make dandelions – along with sunflowers, zinnias, marigolds, and goldenrod – a member of the Aster Family, one of the most successful plant families in the world.

Despite their abundance of pollen and nectar, many florets are not pollinated by visiting insects. Individual florets in a dandelion open at the outer edge of the flower head first and sequentially open towards the center. After two or more days, the flower head closes, and those florets not pollinated by visitors can pollinate themselves. The stigma curls even further downward, touches the anther tube surrounding the style, and self-pollinates. This process, called apomixis, can produce viable seeds without cross-pollination. New seedlings grown from these seeds are essentially clones of the parent plant.

Dandelions can bud and bloom, producing flowers and seed heads, from April to November. Each dandelion flower head sits atop a hollow stem, surrounded by a circle of modified leaves called an involucre. The involucre protects the flower throughout its blooming cycle, enclosing it at night or in bad weather and folding downwards to form a barricade against hungry insects when the flower is open. When temperatures rise above fifty degrees Farenheit, buds and then flowers appear on plants. Buds are borne on short stems, which elongate as the flower blooms, raising the flower head above the leaves. Flowers open in the morning and strongly reflect UV light, making them highly visible and a beacon to pollinators.

After opening and closing for a day or two, the involucre then seals the flower head tight for two days. During this time the yellow petals wither away and the pappus grows a stalk to create a parachute for the developing seed. From each floret, one fruit, containing just one seed, develops. The mature seed head opens only when the weather is dry and conditions are right for seed dispersal. At this point, the receptacle also expands – changing from its original cup-shaped container to a convex pincushion – thereby spreading each parachute seed apart, allowing free air flow between them. Now the fully opened seed head is ready for the slightest breeze to lift and carry its many seeds far and wide. This method of wind dispersal gives the dandelion its weedy reputation, for any breeze or updraft may lift and carry the seeds far and wide, where they can quickly germinate and colonize open areas.

Yet the dandelion is vulnerable at this time to seed-eating birds like goldfinches, siskins, and sparrows who might like to snack on its tiny seeds. All throughout its life, the dandelion is a good source of food for animals. In the early spring its tender leaves feed hungry deer, woodchucks, and rabbits. And its early flowers provide lots of pollen and nectar for flies, bees, and other insects at a time when few plants are flowering.

The combination of growth habit, self-pollination, seed abundance, and wind dispersal is the key to the dandelion’s success. As familiar in flower as when it has gone to seed, their flowers and blow-ball seed heads delight and entertain children of all ages. It is said that if you make a wish and blow off all the seeds in one puff, your wish will come true. While they might not grant every wish, wind-borne dandelion seeds ensure there will be plenty of dandelions to wish upon for years to come.

Suggested Reading

Eastman, John, and Amelia Hansen, The Book of Field and Roadside, Stackpole Books, 2003.

Himmelman, John, A Dandelion’s Life, Children’s Press, 1999.

Kottke, Jan, From Seed to Dandelion, Children’s Press, 2000.

Sanchez, Anita, The Teeth of the Lion: The story of the beloved and despised dandelion, McDonald & Woodward Publishing Co., 2006.