I found a wildlife contribution that I had overlooked; it’s from Athayde Tonhasca Júnior, and is especially appropriate for these cold winter months. Click on the photos to enlarge them.
Come in, she said, I’ll give ya shelter from the storm
Life in the mountains can be harsh, even for species adapted to cold temperatures and scarce resources. In these habitats, a mountain avens flower (Dryas octopetala) can be a safe harbour for a fly or the occasional bee. There insects get more than pollen and nectar from the flowers; they also get warmth. The temperature on a mountain avens flower can be up to 30 C higher than the surrounding air.
Warm and cosy mountain avens flowers © SiberianJay, Wikimedia Commons:
Mountain avens flowers are warm because they follow the sun throughout the day, a phenomenon known as heliotropism or solar tracking. Moreover, these flowers are usually bowl-shaped, so sunlight is reflected towards their centre. Heliotropism and flower structure allow the plant to function like a satellite-tracking antenna, maximizing light interception.
A mountain avens flower © Robert Flogaus-Faust, Wikimedia Commons:
A tracking radar © Daderot, Wikimedia Commons:
We don’t know for sure how these flowers rotate to keep up with the sun’s position, but we can assume auxins are behind it. This group of hormones are involved in just about every aspect of plant growth and development, including phototropism (growing towards light).
Left: auxins (pink dots) are evenly distributed in the plant’s tip. Centre: the repositioning of the sun causes auxins to migrate to the shaded side. Right: the concentration of auxin stimulates cells to grow or elongate © MacKhayman, Wikimedia Commons:
Mountain avens’ heliotropism may be similar to what happens with a sunflower (Helianthus annuus) seedling. In the morning, the plant’s stem and upper leaves face east. As the day progresses, auxins move from the western to the eastern side of the plant. Auxins promote water absorption and tissue elongation, so the plant slowly bends westwards. The auxin gradient is reversed at night, and the plant is reoriented eastward. However, this cyclical movement stops when the flower matures. So, contrary to what some people think, fully-formed sunflower blooms do not follow the sun; they are always facing east (although wind or rain can change their position).
Solar tracking of a sunflower plant © Kutschera & Briggs, 2015:
Heliotropism is not the only way for a plant to warm up: fermentation also does the trick.
The stinking hellebore (Helleborus foetidus) is a favourite of many gardeners in Europe and America for its evergreen foliage and the abundance of bell-shaped flowers produced in late winter. The adjective ‘stinking’ is a bit libelous, and so is the plant’s alternative name, dungwort. Although not fragrant, the stinking hellebore produces a strong odour – often described as ‘meaty’ – only when its leaves are bruised.
Stinking hellebore © Uwe und Lukas, Wikimedia Commons:
The stinking hellebore has been peddled since antiquity as a remedy against all sorts of maladies, but this is what the great British naturalist Gilbert White (1720-1793) had to say about the plant’s medicinal properties:
‘The good women give the leaves powdered to children troubled with worms.’ But he added: ‘Where it killed not the patient, it would certainly kill the worms; but the worst of it is, it will sometimes kill both’.
Like related buttercup or crowfoot plants (Family Ranunculaceae), the stinking hellebore is loaded with toxic glycosides.
Although a bad choice as a worm medicine, the stinking hellebore is an excellent option for a garden. It is one of earliest plants to bloom, which can happen even before the snow has melted away. This is a hard time for bees and other insects because there aren’t many other sources of pollen or nectar, so stinking hellebore flowers can be life savers for emerging bumble bee queens.
Bees may have another good reason to visit these flowers: the warmth generated by yeast metabolism. Stinking hellebore nectaries are colonised by some types of yeast that ferment the nectar and warm the flower to more than 2° C above the ambient temperature. Yeasts have a negative side too: fermentation reduces the sugar content of nectar, which makes the flower less attractive and rewarding to pollinators. We don’t know how these conflicting outcomes pan out for plant and pollinators. Flower yeasts however, seem to be clear winners; they get energy from an abundant supply of nectar, and are dispersed from flower to flower by insects:
Cell formations of Metschnikowia reukaufii, a yeast frequently found in flowers. Bar = 50 μm © Magyar et al., 2005:
Floral warming is an asset for plants with short growing seasons: the extra heat accelerates pollen germination and the growth of pollen tubes, and it leads to heavier seeds and higher germination rates. It may also increase the evaporation of volatile organic compounds, which help in attracting pollinators.
Warm flowers increase insects’ metabolism, boost their flight capability, and encourage them to stick around, basking and foraging. Frequent and long-lasting insect visits are important for upland plants that cannot self-fertilise and rely mostly on flies for pollination. These insects lack pollen-carrying structures and, generally speaking, are much less hairy than bees. So the longer a fly frolics on a flower, the greater the chances it will get pollen grains stuck to it. With luck, some of these grains will be carried to another flower, and pollination will happen.
A warm welcome pays off for plants and insects alike.
Spilogona sanctipauli, a fly from the family Muscidae distributed across the High Arctic and a pollinator of the mountain avens © BoldSystems, Creative Commons.