Lesson Three
The Lake
It's a bit breezy out here, isn't it? The winds whipping the surface of the lake into quite a frenzy. Or perhaps that's the giant squid...
Now, I know many of you can't wait to dive in for a closer look but I'm afraid you'll have to wait a little while. Because it's hard for me to give explanations while we're under the water, we'll have to do the teaching part up here first.
Aquatic Ecosystems
Water has minerals dissolved in it and the particular types of
minerals in a body of water will affect what plants can thrive there.
It's not all down to minerals though: how deep the water is, the amount
of light that can pass through it, the temperature and whether it flows
quickly, slowly or not at all will all impact what grows there.
Plants are very important in a water-based ecosystem. They're the main source of food and shelter for a lot of the creatures living there. Their roots and leaves also help to stabilize the floor and sides, stopping the mud, sand and stones from being worn away by the water.
Aquatic Plants
Plants that live in or near water are called aquatic plants, macrophytes or hydrophytes. Many have special features that enable them to live in watery conditions.
For instance, plants that grow in the air tend to be quite strong and rigid, whereas aquatic plants are often softer, lighter and more flexible. This is because aquatic plants can rely on the water to support them.
Some plants, called submerged plants, will have their roots buried in the lake floor and exist entirely under the water. Others, known as emerged plants, will root on the floor but have their flowers and leaves above the surface. Floating plants do without being rooted to the bottom at all and float freely, going wherever the water takes them. That's the case with some types of water weed - you'll often see them bobbing by in huge, tangled mats.
For an example of a plant which roots itself in the lake bottom, let's head over here to take a look at this patch of water lilies. The plants' huge round leaves and showy flowers float on or near the surface, while their roots are buried in the mud under the water.
You'll commonly see two varieties in the UK: the white water lily with leaves of up to 30 cm and the yellow water lily with leaves of up to 40 cm (also called 'the brandy bottle' due to its distinctive scent). There are hundreds of others around the world though, with some particularly vibrant specimens found in tropical habitats.
Water lilies belong to a family of plants known as Nymphaeaceae, a Latin term that refers to the water nymphs of classic mythology. The jury's still out on whether water nymphs actually exist, though some magizoologists swear they've seen fairy-like creatures skipping over the surface of ponds and lakes by moonlight. Water lilies are also the source of a risky magical practice, where people use charms to strengthen the leaves to create stepping stones to cross the water. Before anyone gets any bright ideas, let me assure you that anyone caught doing that at school will have more than damp robes to worry about.
Plants like the water lily rely on their large, flat leaves to help them to float. Other aquatic plants take a different approach: they have thin, flexible leaves that enable them to move with the water.
Gillyweed, one of the most famous magical plants of them all, grows in this way. I'm afraid I only have a small sample here, so you'll have to gather round to see. Now, it doesn't look very pretty, does it? A lot of people say it looks like slimy, greyish green rat tails (and they have a point). Those tendrils are useful though as they can flex and move with the currents.
Gillyweed is powerfully magical and allows anyone who eats it to survive under water for a time, by growing gills and webs between their fingers and toes. It was first discovered by Beaumont Marjoribanks, but its magical properties only came to light when Elladora Ketteridge ate some and nearly suffocated. Luckily, she was able to stick her head in a bucket of water in time.
Gillyweed is native to the warmer, saltier water of the Mediterranean Sea. There is some evidence that its magical effects last longer if you're swimming in salt water rather than fresh. It is possible to grow it away from the Mediterranean but the plants are always much smaller and weaker. I cultivate a few gillyweed plants here at Hogwarts but I won't be telling you precisely where (just in case anyone has any grand plans for a midnight swim).
Lake Shore
Now, I said earlier that the term macrophyte included plants that grew near water, not just in it. There are plenty of plants that grow in the shallows at the edges or on the shore that are worth a look. Our particular lakeside is home to herbs like water mint and water cress but also to beautiful flowers, like the vibrant red water lobelia.
You see that huge patch of yellow flowers on the shore, where the ground has been slightly churned up? That's silverweed, which you might have used in potions before. It gets its name from the fine silver hairs that cover its sawtooth leaves. Silverweed is a useful all-purpose potions ingredient, though it's particularly celebrated for its anti-inflammatory properties. Many people like to add a few leaves to their Pepperup Potion to soothe sore throats and swollen sinuses.
It has many historical uses too. Roman soldiers would line their boots with its leaves and the roots were a valuable source of food prior to the spread of the potato. Silverweed has long been used to ward off dark forces - ironically, muggles used to think it helped protect against witches!
Then there's bladderwort. You can't see it very well as it mostly exists under the soil or water but it's one of the most interesting examples of a carnivorous plant that I've found. It has tiny bulbs (bladders) that suck in water, dragging tiny organisms in for the plant to feast on. Many herbologists have argued that magic must be involved for a plant to have created such a clever technique but we're still not at all sure.
Lastly, I should caution you against hemlock water-dropwort. It's different to the hemlock you may encounter in the woods, though both are highly poisonous. While it doesn't often grow this far north, it's very common in other parts of the country and is one of the most toxic wild growing plants in Britain. It grows upwards of 1.5 metres and its leaves are triangular. It has distinctive stems which are hollow, tube-shaped and grooved. It's particularly dangerous as it smells very attractive (like parsley or celery) and its roots resemble parsnips. There have been many cases of accidental poisonings where unsuspecting witches and wizards have added it to their cauldron, mistaking it for a safer plant. This is why I'd advise all of you to carry a vial of The Antidote to Common Poisons whenever you're using plants gathered in the wild!
Now, I think there's just enough time to see some aquatic plants in situ. If you'll all line up, I'll perform the bubblehead charm for anyone who'd like to go under the surface. Remember to watch out for grindylows!