What Fruit Has Seeds on the Outside?

In the fantastic world of angiosperms -- plants that flower and reproduce sexually -- millions of years have allowed vast variety of flowering and fruiting habits. Fruits shelter many seeds against predatory birds and animals until the rotten fruit falls, releasing the mature seeds. Two familiar fruits that apparently grow their seeds on their outsides -- strawberries (Fragaria x ananassa) and cashew apples (Anacardium occidentale) -- are more complicated than they seem.

Strawberries grow as perennials in U.S. Department of Agriculture plant hardiness zones 5 through 8, but can be treated as cool-season annuals in USDA zones 9 and 10. A June-bearing strawberry variety, "Honeoye" grows in USDA zones 4 through 9. All are ground-hugging garden plants that spread by runners. The brown "seeds" that cover the surface of the berry are achenes -- fruits that protect a tiny strawberry seed inside. The sweet red berries are swollen receptacles that emerge as the plants' five-petaled flowers fade.

Cashew apples are tropical evergreen trees. The cashew fruit grows at the end of a pear-shaped red or yellow receptacle, called an apple, that is part of the plant's stem. The fruit encases the nut in two hard covers and a layer of acrid liquid, but the entire case is planted to grow a new tree. Cashew trees grow only in the frost-free climates of USDA zones 11 through 12. They require daytime temperatures above 50 degrees Fahrenheit and 40 F at night, so they require shelter in cooler zones.