Beyond the Arctic Circle: discovering plants in Tromsø

Elverhøy is situated on the summit of Tromsø island in northern Norway. In June this pleasant residential area is home to neatly mown lawns bordered by luxuriant clusters of vibrant flowers including cornflowers, aquilegias, campions and geranuim. This year I had the privilege of spending a week of glorious weather and endless daylight here. Tromsø, with a population of around 70,000, is over 300 kilometres north of the Arctic Circle. Between mid May and mid July the sun never sets. Given these extreme conditions I was unsure what plant life I would encounter. What follows is a little of what I learnt and observed.

The variety of species in subarctic climates is limited. In general, conifers dominate the boreal forests due to their ability to withstand harsh winters. Their cone shape minimises the amount of snow that remains on the trees and their multitude of needles maximises their potential area for photosynthesis. As Tromsø benefits from the gulf stream, an ocean current carrying warm water up to northern parts of Europe and North America, temperatures are much milder here compared to locations further inland. Broad-leaved trees with shallow roots, such as birches (Betula sp.) and rowans (Sorbus), are also therefore present.

Perennial flowers around Tromsø grow quickly. The growing season is short and during this time there is almost continuous sunlight. Colours appear to be more vivid, perhaps to attract the more limited number of pollinators at this latitude. European Globeflower (Trollius europaeus) can be seen in various locations around the city. It has a tall hollow stem, lobed leaves growing from the base of the plant (known as basal leaves) and very distinctive bright lemon-yellow ball-shaped flower heads.

In the higher areas, plants grow close to the ground to protect themselves from cold winds and have smaller leaves to retain moisture. One such plant is Mountain Avens (Dryas octopetala), a small evergreen shrub with dark green wrinkled leaves on the top side and white hairs on the underside. Its Latin name refers to the fact that is has eight petals which is somewhat unusual for a plant of the Rose family whose members generally have five petals. Frost-resistant, the Mountain Avens can live for over 100 years in the wild [1]. It is the national flower of Iceland where it is known as Holtasóley and is used in tea.

Ironically, the emblematic plant of Tromsø, Persian Hogweed (Heracleum persicum), locally referred to as Tromsøpalme (« Tromsø Palm »), is an invasive species [2]. Originally from mountainous areas in Iran, where the seeds are used as a spice in Persian food and also for treatment of respiratory, gastrointestinal and urinary problems [3]. Several versions exist to explain its arrival to Tromsø. According to one claim, it was brought to the area by a British travelogue, W. Christy, in 1836. Others believe that the seeds arrived through trade with northern Russians. Growing up to 1 to 4 metres in height, it is easily recognisable due to its thick reddish hollow stem, alternatve leaves which are longer than they are wide and its umbels (umbrella shaped clusters) of small pale white and lime-green flowers. Dispersed by the wind, water and car tyres, the seeds spread rapidly. Due to its imposing size (and thus shade) and its chemical composition, it is feared that the plant may stunt or prevent the growth of other plants. It is closely related to the Giant Hogweed (Heracleum mantegazzianum), another invasive species. The sap of these two plants contains furanocoumarins which can cause severe skin irritation when combined with light [2]. Dry stems and umbels of Tromsøpalme remain visible throughout the year and often feature in photos, postcards, local art and jewellery [4].

The summertime is an ideal time to discover local flora in Tromsø or elsewhere. As the Norweigans say « Ut på tur, aldri su », there’s never a reason to be grumpy when you’re enjoying nature outside !

For more information on plants in Norway, see "Welcome to the world's most northerly botanical garden!" and "Cloudberries in the midnight sun".

[1] https://herbaria.plants.ox.ac.uk/bol/plants400/Profiles/CD/Dryas

[2] Meier S, Taff GN, Aune JB, Eiter S. Regulation of the Invasive Plant Heracleum persicum by Private Landowners in Tromsø, Norway. Invasive Plant Science and Management. 2017;10(2):166-179.

[3] Majidi Z, Sadati Lamardi SN. Phytochemistry and biological activities of Heracleum persicum: a review. J Integr Med. 2018 Jul;16(4):223-235.

[4] Alm T. Ethnobotany of Heracleum persicum Desf. ex Fisch., an invasive species in Norway, or how plant names, uses, and other traditions evolve. J Ethnobiol Ethnomed. 2013 Jun 24;9:42.