We continue this 4-part series on strawberry anatomy by now focusing on the mature fruit. See also, part 1 – the flower.

All the structures of the flower are present on the mature fruit, they just look a little different. The calyx is slightly expanded and sits at the “top” or “stem end” of the fruit which is why it’s called the “cap” by growers and processors. It can be large and leafy, extending well beyond the fruit’s perimeter (Fig. 1 left), or quite small (Fig. 1 right).

The calyx is made up of several sepals (Fig. 2). The primary function of the calyx is to protect the internal parts of the flower bud from damage and desiccation. It also provides support for the petals once the flower opens. Sepals are capable of photosynthesis, although at a lower rate than leaves due to lower stomatal density. We’ll talk about stomata when we get to leaves in part 3, but for now, these are the tiny openings in the leaf that allow for gas exchange and transpiration.

Beneath the calyx of mature fruit you’ll find the remnants of the stamens. You might have thought they disappeared but they’re still there, just dried out, having served their purpose of providing pollen (Fig. 3).

It takes about 25 to 30 days to go from bloom to fruit and by then the petals have usually shed and blown away. However, depending on the shape of the top of the fruit and the size of the calyx, they might get caught between the calyx/sepals and the fruit surface. A fruit with a recessed pedicel (the stem connecting the fruit to the plant) and a large calyx is more likely to trap petals. This is one of the factors contributing to Botrytis fruit rot since a calyx-petal-fruit surface sandwich will trap water, allowing the moisture to persist and provide ideal conditions for the fungus to germinate and infect the fruit (Fig. 4).

The seeds or “achenes” which were tightly packed on the receptacle during bloom are now spread out on the enlarged fruit surface. If you look closely, you’ll see the remnants of the pistils attached to each achene. These are now dried and brittle, having served their purpose of receiving pollen and fertilizing the ovary which is now the tiny seed or achene. They will break off at the slightest touch and might look like a kind of dust to the untrained eye (Fig. 5).

Over the course of about 25 to 30 days, depending on temperature, the receptacle transforms itself from a small yellow dome into a large, soft, red, sweet, and fleshy fruit. If you make a cross section through the fruit, you can see the vascular bundles extending from each seed into the pith. Each variety will show this a bit differently with some being very conspicuous and others barely noticeable (Fig. 6).

This is the goal of every strawberry grower: to produce as many of these delicious beauties as possible and get them to market before they shrivel or decay. It’s a tall order but California growers do it very well.

That’s it for part 2. Part 3 will focus on the leaves.

Answer to yellow spots on sepals in Figure 3: That’s angular leaf spot caused by Xanthomonas fragariae. It infects leaves and sepals which are anatomically and functionally similar. See an earlier blog post titled “Prime time for angular leaf spot“.