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There's a lot going on in a leaf 😉

16.6.21

There’s a lot going on in a leaf - thousands of chemical reactions occur in each one as part of photosynthesis – the process plants use to turn sunlight into energy. Each plant develops their own unique blend of ingredients from sunlight, water, and the nutrients they pull from the soil.

Plants also very cleverly have their own immune system. The unique makeup of each plant gives it distinct benefits by making it more resistant to pests - they literally make their own, amazing, natural pesticide. Bugs and fungus want to eat the plant’s sugar, yet plants are clever enough to makes their own protection via their own sugar - not daft, these plants. So, the plant creates a substance called resveratrol (resveratrol is a one of many plant compounds called polyphenols, which are powerful antioxidants), which kills the bug if it eats it - clever little plant! It just so happens that these properties can also be beneficial to horses. And us humans too - red grapes are especially high in resveratrol, and red wine is just one perk giving us plenty of this potent nutrient. 😊

These beneficial components are highly concentrated in the leaves of some plants, although some are also stored in barks, roots, seeds or flowers. Herbalists rely on the leaves of plants like mint, lemon balm and nettle for their medicinal properties, but we also rely on leaf shape as one of the ways to identify a plant. The terminology can seem a little confusing at first but once you learn that each leaf is made up of distinct zones, it soon starts to make sense.

First, there's the blade. Most leaves have a stem (or petiole) that attaches the leaf to the rest of the plant. The petiole sometimes extends into the leaf and divides the leaf into two equal halves, and when it does it’s called the midrib. The thin, leafy portion on either side of the midrib is called the blade.

The base of the leaf is the portion where the petiole - the stem - comes out to attach the leaf to the rest of the plant, and the apex is the other end – the tip of the leaf.

Leaf shape

Many different terms describe the shape of a leaf, but here are some of the most common ones :

  • Cordate - heart shaped, with a sharp tip at the apex and the petiole coming out between the rounded parts of the heart at the leaf base.
  • Elliptical - longer than wide, but tapers at both ends.
  • Lanceolate - longer than wide, but tapers smaller at the apex.
  • Linear - narrow and the same width at both ends.
  • Ovate - egg shaped and widest at the base.

And a few different shapes of the base and apex:

  • Acuminate - an apex that tapers to a long, thin point.
  • Sagittate - a base that looks like the base of an arrowhead.
  • Truncate - a square base.

Also, a leaf can be either simple or compound. A compound leaf has smaller leaflets that connect to the midrib with stems of their own, while a simple leaf is made up of a single blade.

Leaf edges

The edges of the leaf, the margins, provide more important identification clues. If the margins are smooth, the leaf is described as entire. If there are teeth or notches along the edge, though, there are a few different ways to describe them:

  • Cleft - rounded shapes with notches more than halfway to the midrib.
  • Crenate - small, rounded teeth.
  • Dentate - sharp teeth that point outward.
  • Entire - a smooth margin with no teeth, notches or other textures along the edge of the leaf.
  • Incised - margin cut with irregular teeth that may have deep notches toward the midrib.
  • Lobed - rounded shape with notches less than halfway to the midrib.
  • Serrate - teeth that point toward the apex.
  • Sinuate - a wavy edge, larger than crenate and not as pronounced as lobed or cleft.

Attaching to the stem

The next clue to look at is how the leaves attach to the stem of the plant. The place where the petiole meets the stem is called the node. A node can have more than one leaf or only a single leaf:

  • Alternate - a single leaf at each node. A leaf on the left with nothing across from it, then a leaf on the right a little above or below.
  • Opposite - two leaves at each node, one on the left and one on the right and directly across from each other.
  • Rosulate - a cluster of leaves at the base of the plant that form a rosette pattern. Usually, these have very short nodes and petioles.
  • Whorled - leaves that form a circle at regular points along the stem.

I loved my early days of studying basic botany - I fondly remember my first year of studying Medical Herbalism, using my newly purchased and very tiny magnifier to open up my world of awesome leaf anatomy - meadowsweet was amazing - very hairy!

I still disappear into bliss mode when I get my magnifier out and get up close and personal with a leaf, identifying all the different the leaf shapes I come across. Who knew I'd ever become a leaf nerd?!