Oak tress begin to produce acorns in late September, and they continue to produce them until December. Green acorns begin forming at the tips of branches in groups of three to five. When the acorns mature, they turn dark brown.
An acorn is a seed encased in a shell. The lower end of the acorn contains the root and stem, and the rest of the acorn is composed of tissue filled with nutrients. Many species of birds and animals eat acorns, and acorns are the main food source for some of these animals. There are 58 species of oaks that produce acorns in the United States. Some produce small acorns, while others produce much larger ones. A single oak tree is capable of producing thousands of acorns in a single year.