Developing into massive shade trees, pecan trees (Carya illinoiensis) mature at 70 to 100 feet tall and 40 to 75 feet wide. Native to the south-central United States and Mexico, they grow best in deep, moist soils across this region. Flowering in spring, the fruits with a tasty meaty core, the pecan "nut," more consistently ripen where summers are long and hot. Grow pecan trees in USDA hardiness zones 5 through 9.
In early spring, both male and female flowers occur on the branches of pecan trees. Male flowers look like pendant chains, called catkins, and release their pollen to the wind. Female flowers on the same tree, found in clusters of two to 10, are not receptive to the pollen so another pecan tree is needed to release pollen that coincides with the female flowers opening. This is known as dichogamy. The pollen, once airborne, can travel for miles in a strong wind, according to the University of Georgia.
After pollination, a female blossom develops into an oblong fruit or "nut" that is 1 to 2 inches long with a husk that has four sutures. The outside of the fruit is green and fleshy and called the "shuck." Inside the fruit is a hard pericarp or "shell" that houses two kernels separated by a thin papery plate. The fruit is harvestable when the shuck separates from or splits open to reveal the shell. The shell must be opened to release the edible kernels--the pecan nut.
According to the University of Georgia, 100 g of pecans provide 687 calories. Of this weight, nearly 10 percent is protein, 15 percent carbohydrate, 2 percent dietary fiber and 72 percent fat. The pecan is rich in thiamin (vitamin B1) as well as phosphorus, potassium and iron.
The National Pecan Shellers Association reports that pecans "rank highest among all nuts and are among the top category of foods to contain the highest antioxidant capacity." Antioxidants may diminish risk of coronary heart disease, cancers and some neurological diseases. The sterols in the nut meat also can help lower cholesterol levels and it is low in the saturated fats that are considered unhealthy.
Pecans comprise only a trace production amount outside of North America. The United States by far is the largest producer of pecan fruits. The University of Georgia, citing 2004 statistics from the U.N.'s Food and Agriculture Organization, revealed that the United States harvested more than 80,000 metric tons of pecans in that year. It was a below-average harvest, with 95,000 to 160,000 metric tons being more typical. Mexico is the second-leading producer of pecans.