Carya illinoinensis, also known as pecan, is a large, deciduous, lowland tree, the largest of the hickories. It typically grows 75 to 100 feet tall (infrequently to 150 feet) with a large, rounded, spreading crown and trunks that mature to 2 to 4 feet in diameter. It is native along the Nueces River in Texas but has spread from Iowa, Illinois, Indiana, and Ohio, south to Alabama and Mexico, being primarily found in the Mississippi River Valley and the valleys of its principal tributaries. In Missouri, it occurs in river flood plains and margins of river bottom prairie, mostly in counties bordering the Mississippi, Missouri, Osage, South Grand, and Grand Rivers (Steyermark). It is the state tree of Texas. Pecan features medium green, odd-pinnate compound leaves, with each leaf having 9 to 17 pointed leaflets. Leaflets range from 2 to 7 inches long. They mature to yellow-green in summer, eventually turning yellow-brown in fall. Non-showy, monoecious, greenish-yellow flowers appear in late May; the male flowers in pendulous catkins (to 4 inches long), and the female flowers in short spikes. Female flowers give way to sweet, edible nuts. Each nut is encased in a thin husk, which splits open in four sections when ripe in fall. Pecans are an important commercial nut crop in the U.S. Most commercial operations are located in the southern U. S., from North Carolina to Florida, west to Arizona and California. Many cultivars are available. Pecans are sometimes grafted onto the roots of other hickories (e.g., Carya cordiformis) so they can be planted further north of their normal growing range. They have no serious insect or disease problems, but scab can infect both nuts and foliage; however, scab resistant cultivars are available. Aphids, pecan weevils, twig girdlers, and fall webworms can also do damage.