Here we are looking at sun and shade leaves. This is useful for natural navigation as it can help us to determine the sun’s dominant location in the sky. With this simple knowledge it can allow us to work out which way we are heading.
Lets use Ivy as an example, it is the most readily available plant in most gardens and streets so can be easily identified and studied. It is also an extremely adaptable plant, which is why it is so pervasive in our gardens.
Ivy starts of life as a sciophyte. Sciophytes are shade loving plants or trees, they have specially adapted leaves that maximise the absorption of light without the worry of drying out from the heat of the sun. Ivy will therefore grow really well under the shade of trees (think bases of trees, woodland floors) and will establish itself quite well.
As you can see from the photos above the ivy is only growing on the Northern side of the tree which receives the least amount of sunlight. Growing on this side can be advantageous to plants, that can adapt to it, as there is much less competition for space than there would be in the sun.
Notice that the leaves on the Ivy above are ‘hastate’ (tri-lobed). The ivy in this picture is young and seeks shade however you should notice that it is growing upwards, towards the light after all, once it is at the top of the tree, it will struggle to find a shady spot.
Below are two more photos, of the same plant. Before you say he’s got the wrong plant there! I can assure you they are both ivy, but notice the difference. The ivy in the first ‘sun’ picture has smooth ‘lancolate’ (lance like) leaves, smaller, lighter, thicker, shiny leaves. The leaves in the ‘shade’ picture have large, darker, thicker, dull leaves.
What has happened?
Well… the ivy has grown and, after a period of approximately four years, it develops from a sociophyte into a heliophyte, a sun loving plant. Think of this stage as the plants adolescence, the period before it flowers and produces seed. A time in its life when it will need more energy in the form of sugar created by the process of photosynthesis. Something it would struggle to do with those low sugar producing shade leaves.
It goes through this change so it can maximise the advantages of being exposed to strong sunlight that would otherwise dry out, and kill the initial well adapted shade loving leaves it produced earlier in its lifecycle.
You’ll notice that in the shady areas the Ivy will retain some or all of its shade loving leaves but will put all of its attention into growing towards the sun, and creating those spear like leaves specially adapted to harvest the sunlight.
This process of adaptation is not exclusive to Ivy nor is it a hard and fast rule. In truth the Process of a plant adapting to sunny or shady conditions is a complex, multifaceted process that happens on a systemic and molecular level. However, if used and combined with other methods of natural navigation it is another brick in the wall of knowledge when combined together will form a strong foundation for finding your way when others don’t.
Most of all enjoy the process of looking closer at the natural world and get outside!
