Why do raspberries have little hairs?
If you’ve ever looked closely at a raspberry, you may have noticed that it sports a number of little hairlike projections. These are leftover flower parts, evidence of a delicious, pollination-powered transformation.
Like most fruits, a raspberry develops from a single flower. Unlike most fruits, however, a raspberry is an aggregate fruit—technically a cluster of many tiny fruits arising from the flower’s multiple ovaries. There are different types of aggregate fruits, but the raspberry (and its close cousins, the blackberry, cloudberry, dewberry, and boysenberry) is an aggregate of numerous drupelets (a drupelet being the minute version of a true drupe, such as a nectarine or plum, which contains a single seed). Each juicy “bump” on a raspberry is an individual drupelet with a single seed inside, and each developed from a separate ovary in the flower. In contrast, most other fleshy fruits, such as tomatoes, avocados, and apples, develop from a flower with a single ovary.
Now back to the “hairs.” The little hairs are the remains of flower structures known as styles, part of the numerous female pistils that helped the flower receive pollen before the fruit formed. Each style connects to its own ovary within the flower, serving to direct the sperm-laden pollen to the right place for fertilization. After pollination the numerous ovaries swell into juicy little drupelets, forming the aggregate fruit. While the petals and other flower structures dry up and fall off as the raspberry matures, the styles often stick around, ultimately becoming the fine, bristle-like projections you can see on the fruit’s surface.
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Some raspberry varieties have longer or more persistent styles, which is why certain batches of berries seem especially hairy. It is worth noting that the soft fuzz on peaches and the wiry bristles on kiwis are not remnant styles, but specialized plant hairs called trichomes, which arise from the epidermis of the fruit itself. Raspberries have trichomes too, but they are nearly microscopic and appear more as a subtle haze on the fruit surface than as hairs to the naked eye.