Alchemilla leaf with water droplets
Plant names often have an interesting history behind them: I came across Alchemilla while looking up a plant I photographed at the weekend. Thinking about the names often helps with remembering them, and also gives insight into the history of the species. Earlier in the year, we discussed the naming of a species after Professor Clive Stace.
More remarkable is the origin of the name of the Alchemilla genus/species. Like many botanist-photographers of Alchemilla leaves, looking from the window I was taken by the lens-like water droplets on the leaf surface – incidentally a plant leaf surface property that is the subject of several papers and another AoBBlog post. Wikipedia mentions the interesting properties of the leaves that lead to the water balling up on the surface, but goes on to add: “These beads of water were considered by alchemists to be the purest form of water. They utilised this water in their quest to turn base metal into gold. Hence the name Alchemilla.”
As a molecular biologist, I have spent many days struggling with less-than-pure water, and much money obtaining pure water. I expect the ancient alchemists were completely correct in their view that the water on the leaf surface, from rain or dew, was as pure as they were likely to be able to find.
Meanwhile, I am using the leaf image as the wallpaper for my computer screen at the moment: the full-resolution image (upper) and lower image are available by clicking on the links or pictures and are downloadable as a jpg file. Right-click and select option to set as wallpaper on a PC or click-wait on Android (for fast loading, may need to be saved after downsizing).
Water droplets on Alchemilla leaves as lenses
What do peacocks, CDs and certain plants have in common? They all have multi-coloured parts – feathers, surfaces or petals – which change their hue depending on the angle you look at them. This physical phenomenon in which an ordered repeating surface structure rather than a pigment gives an object its colour is called iridescence.
Iridescence has evolved multiple times in plants and occurs in a lot of land plant families, from angiosperms to algae and ferns. It can impact on how insects and animals see plants. Dr Heather Whitney, a plant scientist from Bristol University, was awarded the President’s Medal of the Society of Experimental Biology (SEB) last week for her novel and interdisciplinary work. Heather studies how plant surfaces become iridescent and how iridescence influences plant-animal interactions.
Heather started her presentation by talking about how she became interested in her study field. When she went to the Botanic Garden she noticed that even though most flowers of Hibiscus trionum (pictured below) were creamy white, their centre had an oily sheen. So she decided to look at the petals with an electron microscope and realised that the surface looked very structured: The oily sheen on the petals is caused by iridescence.
One way to proof that a flower’s colour is created by iridescence is to replicate the petal structure in epoxy resin, which makes the clear resin shine blue when looked at from a certain angle. This is why iridescence is also called a “structural colour”.
One function of iridescence in plants is to make them more appealing to pollinators. An example is the “sexually deceptive orchid”, Ophrys speculum (pictured right). It pretends to be an animal by mimicking the wings of a female wasps. Similarly, Moraea villosa copies the iridescence of pollinating beetles.
If, like me, you now feel inspired to plant iridescent species in your garden, why not start with tulips?
1. Peacock Head by Cuatrok77 at Flickr. This image licensed under a Creative Commons by licence.
2. Hibiscus trionum flower closeup by la la means I love you. This image licensed under a Creative Commons by-sa licence.
3. Ophrys speculum (plant) by Hans Hillewaert. This image licensed under a Creative Commons by-sa licence.
4. Iridescent Tulip by Anne Hornyak at Flickr. This image licensed under a Creative Commons by-sa licence.