Fruit Anatomy
The presence of structures within a flower, and the form of those structures, has important consequences for the development and appearance of fruits in tree crops. In this section we will examine floral morphology more closely to understand the relationship between flower and fruit structure.
Three Generic Fruit Types: Peach, Apple & Persimmon
Although the tree fruit and nuts grown in California (from cherries to persimmon) vary widely in shape, size, color and flavor, the anatomical differences among most California tree fruit are actually relatively minor. California tree fruit can be grouped into one of three categories based on subtle variation in the flower structures that develop into fruit.
Peach type fruit develop from a single carpel and contain one or two seeds. Peach, nectarine, almond, cherry, plum, prune, apricot, and olive all fall within the common “peach type” fruit (Figure 8).
Apple type fruit develop from multiple fused carpels and contain more than two seeds. Apple, pear, and quince fall within this category (Figure 9). Persimmon type fruit develop from multiple fused carpels and contain more than two seeds. Persimmon and kiwifruit fall within this category (Figure 10).
Relationship between Flower & Fruit Anatomy
Flowers which produce “Peach”, “Apple” and “Persimmon” type fruits
Flower and fruit anatomy are tightly linked, observations of one can provide insight into the pattern of development and appearance of the other. For example, by carefully looking at a flower, you can predict what the fruit will look like as it develops. The position of the pistil relative to the sepals, petals, and stamen is an important determinant of fruit morphology and the extent to which fruit development is dependent upon seed development. Flowers can be grouped into the three categories, which describe the position of the pistil relative to other floral organs, and the presence or absence of a hypanthium (tissue composed of fused petals, calyx, and stamen) (Figures 8-10). A closer look at the anatomy of these three flower types reveals the structural differences between “peach type”, “apple type”, and “persimmon type” fruit they will produce following fertilization.
Perigynous flowers develop into “peach type” fruit
The basal portions of the petals, calyx, and stamen are fused into hypanthium tissue and form a detached, cuplike structure around the ovary. The ovary is in an intermediate position relative to the petals, calyx, and stamen. “Peach type” fruit, formed from perigynous flowers, have no sepals, petals, or stamen attached. These flower structures are shed with the unattached hypanthium as the fruit develops.
Figure 11. Simple cartoon (a) depicting the relative position of petals calyx, and stamen (blue), receptacle (green), ovary (orange), and hypanthium (magenta) in a perigynous flower. Illustration of a perigynous apricot flower (b) and a peach (c) with analogous structures color coded in each.
Epigynous flowers develop into “apple type” fruit
The basal portions of the petals, calyx, and stamen are fused into hypanthium tissue and attached to the ovary. The ovary is inferior (below) the petals, calyx, and stamen. “Apple type” fruit, which develop from epigynous flowers, have remnants of the flower sepals, petals, stigma and stamen attached at the base of the fruit, on the opposite side from the receptacle.
Figure 12. Simple cartoon (a) depicting the relative position of petals calyx, and stamen (blue), receptacle (green), ovary (orange), and hypanthium (magenta) in an epigynous flower. Illustration of an epigynous apple flower (b) and an apple (c) with analogous structures color coded in each.
Hypogynous Flowers Develop into “Persimmon Type” Fruit
The base of the petals, calyx, and stamen are not fused and arise from the receptacle below the ovary. No hypanthium is present. “Persimmon type” fruit have remnants of the sepals and petals attached at the top of the fruit surrounding the receptacle.
Figure 13. Simple cartoon (a) depicting relative positions of petals, calyx, and stamen (blue), receptacle (green), and ovary (orange) in a hypogynous flower. Illustration of a hypogynous persimmon flower (b) and a persimmon (c) color coded in each.
Epigynous Flowers Can Produce Parthenocarpic Fruit
In almost all California fruit crops, some degree of pollination and fertilization is required for seed and fruit development and the number of carpels in a flower determines the degree to which normal fruit development depends on successful seed development and production of growth regulating hormones. However, the presence of accessory tissue is also an important factor determining the relationship between ovule fertilization and fruit development.
For example, in epigynous pear flowers, the hypanthium tissue is attached to the ovary and develops into a significant portion of the pear fruit. The presence of the attached hypanthium in epigynous flowers reduces the need for seed development to stimulate fruit formation. As a result, the Bartlett pear cultivar can produce parthenocarpic fruit when no pollen lands on the stigma to fertilize ovules. Because parthenocarpic fruit develops without fertilization seed growth regulating hormones are not necessary for fruit development in this cultivar.
Image sources for this page: Figs. 11ab, 12ab, 13ab: USDA Handbook 496
Figs. 8, 9, 10, 11c, 12c, 13c: ClipArt Etc website, Univ. of South Florida.