Around the world approximately 450 species of oak (Quercus) trees have been identified, according to Trees for Life. Both evergreen and deciduous oak trees exist They range in height from 50 to 80 feet with a width up to 50 feet, depending on the variety. All oak trees produce a nut known as an acorn. Each acorn contains one to three seeds.
Life Span and Foliage Growth
All oak tree varieties belong to the beech family, Fagaceae. A long-lived tree, the oak can live up to 1,000 years or more. Each spring the oak tree produces new foliage. Evergreen oak trees retain their foliage through the winter months but also produce new foliage with the arrival of spring. The leaves are a favorite food for many pests but the oak tree has learned a way to overcome pest damage. It is one of the few tree's that produces a new flush of leaves during midsummer. The phenomena is known as lammas growth because the growth usually begins around the time of the Celtic festival of first fruits known as Lammas.
Oak trees are both male a female. They produce male and female flowers, which makes them capable of self-fertilization. Each spring when the new leaves appear the tree produces flowers that last seven to 14 days. The male flowers appear as catkins that hang downward. They measure up to 1.5 inches in length. The female flowers appear at the end of the stems as tiny yellowish blossoms.
Each male flower produces thousands of grains of pollen, according to Botany.com. The pollen is carried on the wind to the female flowers. The pollen must land on the female flower's stigma in order for pollination to occur. During the summer months acorns are formed once the female flower is fertilized.
Acorns appear in the fall. A tree must be 40 to 50 years old before an ample crop of acorns will form. Every three to five years a mature tree will easily produce up to 50,000 seeds. Other years the seed production will be scarce.
The acorns fall from the tree in the fall before the leaves fall. Once all the acorns are shed the deciduous trees drop their leaves to cover the acorns. This helps create a moist, sheltered location because germination begins immediately. The leaves hide the acorns from foraging squirrels. It also helps protect the germinating seeds from a hard frost.
The oak tree's root system has a symbiotic relationship with mycorrhizal fungi. The fungi derives nutrients such as carbohydrates and sugars from the oak tree and also supplies the tree with nutrients.