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Taraxacum friesii (Sect. Erythrosperma) [Oslo Dandelion]


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Rørslett, B. 2013. Taraxacum friesii Dahlst. (Asteraceae). Oslo Dandelion. Flowers in visible and ultraviolet light. https://www.ultravioletphotography.com/content/index.php/topic/136-taraxacum-friesii-sect-erythrosperma-oslo-dandelion/

 

Taraxacum friesii Dahlst. (Taraxacum Wigg. sect. Erythrosperma (Dahlst.)Dahlst.)

NO: Osloløvetann

 

This small native dandelion, belonging to the Erythrosperma* section, is endemic to the western coast of Sweden and adjacent Oslofjord region in Norway. It is found in coastal alvar environments so has a preference for almost desert dry calcarous soils.

 

Alvar, or limestone pavement, is a very uncommon biological environment in the regions inhabited by T. friesii. The species itself is Red Listed and the vulnerable environment is regarded as having high value by Nature Conservation agencies. Unfortunately, its distribution conflicts with heavily populated areas putting an immense pressure on the last remains of the alvar biotope.

 

Dandelions are, and rightfully so, infamous for being immensely difficult to identify. Part of the blame goes to taxonomists on an endless quest to describe even more microspecies, part is due to the dandelions themselves because most species are apomictic and genetic variation and mutations is carried directly further by the offspring. Plus, they tend to respond in a plastic manner to changing environmental conditions. Thus there is a bewildering array of dandelions coming in almost any form and size.

 

However, T. friesii is an easily identifiable dandelion because of its most characteristic appearance. The plants are small, often just 10 cm tall. The capitulum is quite small as well, frequently only 2 cm across, and the ligules are golden yellow with a broad light brown stripe on their underside. The styles are yellow, have pollen and are not exserted. The outer phyllaries are spreading or recurved, the inner adpressed. All are corniculate at the tips. Leaves are all in a basal rosette, they are tongue-like with serrated edges and a stout midrib that becomes even thicker towards the base. As far as dandelions go the foliage of T. friesii is unusual by being very stiff, thick, and spiny. Being almost thistle-like is an apt description. The foliage colour is green with a conspicuous bluegreen cast to it and the surface is sometimes slightly pruinose.

 

The plants are always found on shallow alvar soils, in proximity to the sea, and flower in late April or early May. The period of flowering is very short, often just a few days, and seed set occurs quickly thereafter. The fraction of the population going into flowering appears to be fairly low. On the locations I have visited, one mostly observes sterile rosettes. The number of individuals on these sites can be as low as 5-20 so the rarity of this pretty little dandelion is obvious and so is its vulnerability to environmental threats.

 

Each year, I try to follow the status of T. friesii on known sites in my vicinity and the impression is that the number of plants. already very low, is slowly declining. T. friesii has been known from the Oslofjord area since the late 18th century and survived the initial threat from eager botanists and plant collectors. I wonder how it can stand up now to the severe threats to its current locations in this region. Most of the known sites are within recently designated Nature Reserves, but public access, keeping in spirit with the ancient land-use rights of Norway, is not constrained. Maybe the survival strategy of going very quickly through the flowering stage followed by rapid seedset, leads to an inconspicuous plant overlooked or ignored by most visitors.

 

TARA_SECT_ERY_B0905040782_VIS.jpg

Image reference:TARA_SECT_ERY_B0905040782_VIS.jpg

Visible light: Nikon D3X, Voigtländer APO-Lanthar 125 mm f/2.5 lens, daylight**.

 

The stout foliage is readily observed on the habitus picture above.

 

TARA_SECT_ERY_B0905040806_VIS_HABITAT.jpg

Image reference:TARA_SECT_ERY_B0905040806_VIS_HABITAT.jpg

Visible light: Nikon D3X, Nikkor 24 mm f/2.8 lens.

 

This is the typical alvar habitat of T. friesii on the islands of the inner Oslo Fjord. Associated plants forming an open community are Sedum species ( S. acre, S. minimum), Sesli libanotis, Fragaria viridis, Filipendula vulgaris, Polygonatum odoratum, Allium spp., and Artemisia campestris. Soil thickness sometimes is just a few mm or absent, the underlying limestone being colonised by calciphile bryophytes and lichens.

 

TARA_SECT_ERY_I0905048414_UV.jpg

Image reference:TARA_SECT_ERY_I0905048414_UV.jpg

Ultraviolet light: Nikon D200, Coastal Optics APO 60 mm f/4 lens, Baader U2" (Venus) filter, SB-140 flash.

 

The UV pattern of T. friesii is of the central bull's-eye kind, however, the dark centre is fairly restricted in its extension. Styles are brighter than seen under UV for other dandelions, perhaps caused by slight UV-induced fluorescence. Pollen tend to be UV-grey rather than UV-black which also is an uncommon feature within this genus.

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Notes:

 

* Danish taraxacologist H.Øllgaard (personal communication March, 2013) informs me that T. friesii may fit better into the south European section Erythrocarpa, making this species even more different from the other regional species.

 

** Location withheld. These populations are so small that any further impact, such as trampling by man, easily can destroy them.

 

References:

http://www.ultraviol...bjørn-rørslett/

 

[Published 21 March 2013 Last update 25 Aug 2013]

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