Taraxacum Officinale - Evolution Into an All-Year Flower

If one takes a rigorous look at the winter scenery in the northeastern United States in January or February, scattered spots of yellow inflorescence dot the otherwise pallid ground. To the disdain of Americans who view Taraxacum officinale, better known as the tasteless dandelion, as a noxious, aggressive, opportunistic, invasive weed, it has evolved into a year-round flower.

Based on rigorous observations made in southeastern New York and Connecticut since Spring 2006, dandelions have been gift every month of the year (though at a significantly reduced people during the Winter) in the Northeast. This includes January and February regardless of acute short-term or pronounced long-term cold spells and snow cover, which should not be surprising considering that dandelions have been spotted growing in the arctic-alpine regions of Alaska and Siberia (Russia). With their tolerance to a wide range of climates and geographical areas (though most prevalent in grassy areas in temperate regions), long-term climate moderation (even if the Earth may be entering a duration of cooling as some trends indicate), and rising attention of Carbon dioxide (Co2) in the atmosphere, it is likely that Taraxacum officinale will remain a year-round flower necessitating a revision to field guides such as National Audobon's Field Guide to Wildflowers that states the tasteless dandelion blooms from March-September in the northeastern United States.

Taraxacum officinale has evolved into an all-year flower due to a composition of factors based on its characteristics and morphology, and changes in environmental conditions, most notably climate moderation and addition atmospheric attention of carbon-based compounds.

I. Taraxacum officinale Characteristics and Morphology:

Taraxacum officinale can tolerate climatic characteristic readings ranging from sub-zero to low triple-digits as expressed in Fahrenheit (F). Because of its short life span (averaging about 9 days), its capability to increase 18 Kilo Dalton proteins in its roots and its characteristic stunted stems that hug the ground during winter months (note: Taraxacum officinale's stunted stems are extended when the florets wither and dry, producing achenes, to optimize wind dispersal) to exploit geothermal warmth (versus heights of between 2-20 inches during summer months and when achenes are present, minimizing the risk of fluid (a white-milky fluid called latex) icy which could prove damaging or even fatal to many floral species with longer lives especially when they are in a flowering state), the latter two comprising a process called "cold acclimation," dandelions have the capability to survive temperatures as low as -38º F. Likewise, because of Taraxacum officinale's "long, tough tap root that can burrow a foot or more into the soil"[1] to compensate for less than optimal water use efficiency (Wue) versus its close relative the Taraxacum ceratophorum (which is 40.9% more productive based on the results of a study documented by Marcus T. Brock and Candace Galen in Drought Tolerance In The Alpine Dandelion, Taraxacum ceratophorum (Asteraceae), Its Exotic Congener T. Officinale, And Interspecific Hybrids Under Natural And Experimental Conditions (American Journal of Botany, 2005)) and its capability to subsist at reduced photosynthetic levels, Taraxacum officinale can also thrive during hot, dry conditions. Accordingly, based on the study by Marcus T. Brock et al, photosynthetic rate on a per unit area basis under ultimate drought and well-watered conditions did not differ significantly between the two Taraxacum species with each exhibiting similar carbon assimilation (sLightly lower in Taraxacum officinale) and near identical transpiration and photosynthetic rates. In short, Taraxacum ceratophorum develops thicker leaves to enhance water retention while Taraxacum officinale relies on its greater capacity to excerpt water from the soil with its long tap root to endure hot, drought-like conditions visible by the former's higher mean leaf relative water content (Rwc) and mean soil water content (Swc) despite the near identical transpiration and photosynthetic rates of both species. Furthermore, someone else study (conducted by Anton M. Clemmons and David L. Robinson, Inheritance Of Morphological And Physiological Characteristics in Taraxacum officinale at Bellarmine College, Louiseville, Ky, indicated that when Taraxacum officinale plants were exposed to unfavorable heat conditions, they produced genetically enhanced progeny that were better able to tolerate higher temperatures. The same likely holds true for Taraxacum officinale exposed to ultimate cold.

Another factor that enables Taraxacum officinale to thrive in winter months when the whole of pollinating insects (notably bees, butterflies, and hoverflies) is negligible is their capability to reproduce with or without pollination. Taraxacum officinale, which utilizes pollination during spring, summer, and autumn months when insects are in abundance, has the capability to reproduce apomictically or asexually, made inherent by its morphology. Instead of being a single flower, Taraxacum officinale is assuredly a compilation of between 150-200 florets (each consisting of male and female organs) that rub up against each other (accomplishing the same task as insect pollination) during photo- (respond to turn in Lighting conditions) and thermonastic (respond to climatic characteristic change) Movement in which the florets uncurl and open during the day and curl and close during the night. Such nastic Movement is especially beneficial in protecting private florets from degradation when cold temperatures are ordinarily harshest since the closed blossom head provides a protective shield that shelters them from exposure. It also does not hurt that Taraxacum officinale has the capability to regenerate from both its root and stem, should it suffer damage.

Furthermore, because of their apomictic capability and the fact that plants are proactive as well as reactive organisms to their environment, it is likely that Taraxacum officinale reduces nectar (to recompense warm weather insect pollinators which are negligible during winter months) production (a task that can expend up to 37% of energy attained from photosynthesis) to compensate for slowed photosynthetic activity and thus lower energy production because of less than optimal temperatures and reduced hours of sunshine during winter months. It is also likely that Taraxacum officinale reduces nectar production during winter months when it is not essential since in the words of Peter V. Minorsky, Ph.D., Professor of Natural Sciences, Mercy College, Dobbs Ferry, Ny "plants don't waste nectar... [they] ordinarily yield different amounts of nectar during the procedure of [a] day to correspond with the greatest activity of the pollinator. Night blooming plants, for example, only yield nectar during the night." However, experiments are needed to confirm this.

At the same time, despite its apomictic ability, Taraxacum officinale uses nastic Movement and nectar as weapons against neighboring plants to hinder their reproductive capability (which at times has resulted in a negative impact on crop yields while conversely benefiting insect pollinators, especially bees when nectar is scarce during early spring and late autumn). Based on a study documented by Ikuo Kandori, Toshihiro Hirao, Satoshi Matsunaga, and Tsutomu Kurosaki, An invasive dandelion unilaterally reduces the reproduction of a native congener through competition for pollination (Oecologia, 20 January 2009), Taraxacum officinale, with it production of an overabundance of nectar during warm weather months, "attracted more pollinator visits [than Taraxacum japonicum (a native Japanese dandelion), resulting in] negative effects" for Taraxacum japonicum, their congener (a plant that belongs to the same species class), which is not apomictic and thus relies solely upon insect pollination for propagation. Furthermore, based on a study by Osamu Tanaka, Yuuji Tanaka, and Hiromitsu Wada, Photonastic and thermonastic opportunity of capitulum in dandelion, Taraxacum officinale and Taraxacum japonicum (Journal of Plant Research, 21 September 2006), Taraxacum officinale engage in photonastic opportunity at lower temperatures (ranging by as much as 10º F) and for longer periods (ranging from 3-5 hours) than Taraxacum japonicum and someone else close relative, Taraxacum albidum additional exploiting its pollination advantage.

Taraxacum officinale also thrive in all months because of its productive means of seed dispersal (made inherent by its parachute morphology which enhances vehicle and opportunities for survival especially since a breeze of only 1.44 miles per hour is adequate to keep their achenes (seeds) aloft) regardless of environmental conditions and the capability of its achenes to enter a state of dormancy during periods of unfavorable environmental conditions. In fact, Taraxacum officinale seeds can wait up to 9 years to germinate if conditions are not conducive for its survival regardless if they lay on dry land or are submerged underwater.[2] Consequently, in addition to flowering, Taraxacum officinale originate achenes every month of the year.

Ii. climate Moderation and Co2 Ppmv Increase:

Moderating temperatures have also assisted Taraxacum officinale in becoming an all-year flower. Gradually over time, as global mean temperatures have warmed, the original growing season of the tasteless dandelion has been extended deeper into the winter, which at times has meant exposing the plant to harsh cold. Consequently, Taraxacum officinale have likely produced progeny, as mentioned above, to withstand greater winter extremes leading to flowering and seed production throughout the Northeast's winter months as well as expansion to new areas such as the arctic regions of Alaska and Siberia. Prolonged global (prior to the onset of a what is believed to be a temporary duration of cooling), is likely to promote the spread of Taraxacum officinale deeper into tundra-like regions and ensure that its all-year flowering nature becomes the norm instead of an anomaly isolated to a few years.

The rising attention of Co2 levels in the climate also promotes Taraxacum officinale growth. Based on an experiment that exposed Taraxacum officinale to elevated levels of Co2 documented by Tamara M. McPeek and Xianzhong Wang, Reproduction of dandelion (Taraxacum officinale) in a higher Co2 environment (Weed Science, 2007), the plant when exposed to duplicate the normal whole of Co2 (730 μmol (micromoles with a mole being the whole of pure substance containing the same whole of chemical units as there are atoms in exactly 12 grams of carbon-12) mol-1 versus 370 μmol mol-1 from their nascent state until their reproductive maturity) produced 83% more inflorescences and 32% more achenes.

Since 1750, the atmospheric attention of Co2 has increased by 36% to 387 parts per million by volume (ppmv) from 284. It is projected to rise to as much as 541 to 970 ppmv by 2100 if carbon emissions remain unchecked. Per Reproduction of dandelion (Taraxacum officinale) in a higher Co2 environment, "Seeds from elevated C02-grown plants were significantly heavier and had a higher germination percentage, leading to larger seedlings and earlier preparation in the subsequent generation. Furthermore, achenes from plants grown at elevated Co2 [levels] had... Higher stalks at seed maturity, longer beaks, and larger pappi [to] increase the length of seed dispersal by wind [as well as] high[er] competitiveness and [greater] adaptations to disturbance, that [enable it to] increase its vegetative and reproductive success [and] potentially come to be [even] more broad as atmospheric Co2 continues to rise..."

Iii. Conclusion:

Based on the characteristics and morphology of Taraxacum officinale such as its capability to withstand climatic characteristic and other extremes in climate, its capability to reproduce through pollination and apomictically, its capability pass down genetic enhancements to its progeny, and the linked benefits it enjoys from climate moderation and rising levels of Co2 in the atmosphere, the tasteless dandelion has evolved into a plant that flowers and produces seeds in every month of the year. Based on long-term trends with regard to atmospheric composition and climate change, it is likely that Taraxacum officinale has constantly come to be an all-year plant in the northeastern United States regardless of month or season and will likely continue to spread to new geographical venues.

[1] Dandelions. 11 January 2010. http://www.almostgruntled.com/stories/freelance/dandelion.html

[2] The assistance of Achene in Dandelion Dispersion. 16 January 2010.

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