Want to know the blackberry’s biggest secret?

That juicy little fruit you pick from hedgerows, bake into crumbles and stir into jam, technically speaking, is not a berry.

So, in honour of National Blackberry Day on September 12, let’s gently expose one of the fruit world’s greatest identity crises.

In everyday life, we tend to call small, soft, juicy fruits “berries”. Strawberries, raspberries, blueberries, blackberries - if it looks good on top of porridge or beside a pavlova, we are probably calling it a berry.

Botanists, however, have a stricter definition, they don't consider taste or appearance, but rather how the plant's flower and adjoining parts develop into a fruit.

In flowering plants, fertilisation initiates both seed and fruit development. The ovule (the precursor to the seed), if fertilised by pollen, becomes a seed. The tissue surrounding the seed is the ovary. As the ovary matures into fruit, its wall thickens and differentiates into three distinct layers.

In order to achieve “berrydom,” a fruit must meet three criteria. First, it must have three fleshy and distinct layers. Second, it must have two or more seeds. Finally, a true berry develops from one flower containing a single ovary. That means some familiar fruits do count as true berries such as grapes, tomatoes and bananas.

According to the Irish Wildlife Trust, the blackberry is not a berry in the botanical sense, but an aggregate fruit made up of small drupelets.

Each blackberry flower contains lots of tiny ovaries. When the flower is pollinated, each of those ovaries develops into a tiny individual fruit called a drupelet.

Those little bumps that make up a blackberry? Each one is its own mini fruit, complete with its own seed.

Here is where things get wonderfully ridiculous.

Meanwhile, bananas are berries. Tomatoes are berries. Avocados are berries. Pumpkins and watermelons are also, botanically speaking, berry-like fruits.

Whether it’s a berry, an aggregate fruit, a drupelet cluster or a tiny hedgerow miracle, the blackberry remains one of September’s much loved wild harvest.

It still belongs in warm crumbles with melting vanilla ice cream. It still makes beautiful jam, turns apple pies into something special and it works in compotes, cocktails, breakfast bowls, sauces, cheesecakes, smoothies and bakes.

It still tastes like the end of summer and the start of autumn.

And across Ireland, north and south, it still has that lovely sense of nostalgia: plastic tubs, scratched arms, purple fingers, country lanes, garden walls, and the quiet satisfaction of finding a patch the birds have not beaten you to.