PLANT OF THE WEEK
Dr. T. Ombrello - UCC Biology Department
Common names: Dandelion, Common Dandelion, Lion’s Tooth, Blow Ball, Puffball, Cankerwort, Monk’s Head, Priest’s Crown, Fairy Clock, Peasant’s Clock, Doonheadclock, Fortuneteller, Irish Daisy, Swine Snort, Pissabed.
Scientific name: Taraxacum officinale
Explanation of scientific name:
Taraxacum – the Latin version of a native Arabian name. The name appeared over 1000 years
ago in medieval Arabic writings as taraxacon. In Greek taraxos means disorder
and akos means remedy.
officinale – medicinal, of the pharmacopoeia, in reference to the many historical uses of this
species in medicine.
Mention the word “Dandelion” to a typical gardener and you are likely to get a negative response. This bane of the perfect lawn has been the source of suburban neighborhood unrest, as homeowners with dandelion-free lawns demand that neighbors with dandelion infestations do something to control the weed before its seeds blow onto their lawns. In any horticultural setting, dandelions can be serious competitors with other plants, so their reputation as an aggressive, difficult to eradicate weed is well deserved. Will gardeners ever win the battle against dandelions? Probably not! While herbicides can effectively kill them and prevent their seeds from germinating, cultivation can cut them up, and specially designed dandelion extraction tools can remove them, they still manage to come back. There is no realistic hope that we will ever be able to eradicate this species. Perhaps the best we can hope for is limited control. We are not likely to win the battle against dandelions, and other weeds for that matter, because they have nature on their side. A dictionary definition of a weed will read something like “an unwanted plant” or “a plant out of place.” From the human perspective that may be true, but from the ecological perspective they have an important role in nature. They have been playing this role for eons of time, and have become quite good at it. That role is the early colonizer of disturbed sites. When a natural disaster such as a fire, flood, geologic disturbance, or extreme weather destroys the vegetation in an area, it is the weeds of the world that quickly re-vegetate the site. By stabilizing the soil and preventing wind and water erosion, along with providing cover and food for animals, they make it possible for the pre-disaster community of life to return and re-establish itself. Once the dandelion or other weed has completed this role, it leaves only its seeds in the ground, waiting to emerge after that next disaster. Long-term studies, still ongoing, show that some weed seeds can remain viable in the soil for over a century, and readily germinate once the soil is disturbed around them. Most horticultural endeavors, from backyard gardening to large scale farming, usually begin with destroying the existing vegetation, followed by turning the soil over, and finally sowing plants that we want to grow there even though they most likely are not native to the area. We create the perfect environment for weeds to get established, and then pit them against plants that are not as competitive unless we help them. Is it any wonder that the weeds, as exemplified by the dandelion, often win?
everyone sees the dandelion as an objectionable weed.
explanation above of the dandelion’s scientific name suggests, this species has
a history of medicinal use in its native range of Europe and
The milky latex found in dandelions, and especially their roots, has the potential to be a source of rubber. Taraxacum officinale can be used, but it is inferior to other species of dandelion. During World War II several Eastern European nations grew vast fields of dandelions for rubber production since tropical sources were unavailable. Today, several species of dandelion are being investigated for commercial rubber production.
The dandelion is a member of the Sunflower family of plants (Asteraceae). This huge and diverse family contains over 22,000 species. Besides sunflowers and asters, dandelions can count chrysanthemums, marigolds, lettuces, and artichokes as close relatives. The dandelion is an early successional herbaceous perennial, meaning it consists solely of soft tissue, has an indefinite lifespan, and is commonly found on disturbed sites in nature. The plant grows in a rosette fashion, with all the leaves arising from a very compact stem (crown) just below the soil surface. The species’ leaf habit can be quite varied. Some plants produce leaves that are upright and almost vertical, while others produce ground-hugging leaves that are essentially horizontal. Leaves are spirally arranged on the stem, typically with every sixth leaf overlapping one below it. This affords the leaves maximum exposure to the sun. The irregular, jagged teeth on the linear leaves led to the common name of the plant. Dandelion is derived from the French dent de lion (tooth of a lion). The plant is anchored by a long, white, fleshy taproot with amazing capabilities of regeneration. If part of a root remains underground after a plant is pulled or cut from the soil, it usually develops one or more new crowns and leaves. The root not only stores reserve energy for the plant, but also taps moisture and nutrition from well below the soil surface. In a sense it improves the soil for the plant community by breaking through compacted subsoil and moving nutrients closer to the surface.
Dandelions reproduce by seeds, and do so quite successfully. The plants bloom in response to day length. Known as “short-day” plants, flower buds are usually initiated when a growing plant experiences nights in excess of 12 hours. The dandelion’s familiar yellow flower atop a long hollow stem is not really just a flower, but instead an inflorescence of many small individual flowers attached to a globe-like receptacle. Each flower produces a seed enclosed in a tiny, hard fruit known botanically as an achene. Each of the many achenes of a dandelion inflorescence is topped by a pappus of numerous fine hairs that when dry helps the achene and the seed it contains become dispersed by even a slight breeze in a parachute-like fashion. Children and adults alike enjoy picking ripe dandelion heads and blowing the achenes into the air, inadvertently helping to spread the plant throughout their neighborhood. Dandelion seeds can be produced by sexual and asexual reproduction. The sexual method involves sperm within pollen grains reaching the eggs within ovaries, often with the help of pollinating insects. This is the method the majority of plant species employ to produce seeds, but not dandelions. Most dandelions produce seeds by apomixis, where unfertilized egg cells in the ovaries produce viable seeds that will germinate to become clones of the parent plant. The plants reproducing by apomixis are polyploids (mostly triploids) with an irregular number of chromosomes in their cells. A population of dandelions can contain plants reproducing by both methods. This flexibility in seed production, with both asexually and sexually reproducing individuals in a population, allows for some diversity within each generation, while permitting adapted asexually reproducing individuals to clone themselves. This is just another little feature of this amazing species that makes it so successful.