Oranges, grapefruits, lemons and limes are examples of citrus trees. These tropical fruit trees are angiosperms, reproducing sexually with flowers. The life cycle of citrus trees begins with a seed.
Oval and about 4 millimetres long, each citrus seed contains an embryo and starches held within the seed coat. When the seed is exposed to good soil, light and water, the seed germinates and starts growing.
As the seed grows, it sprouts roots, a stem and leaves. The starches within the seed feed the new sprout, at first. Later the seedling absorbs water and mineral nutrients directly from the soil and uses sunlight to convert them to sugars that feed the plant and allow it to grow to maturity.
Citrus trees reproduce sexually by growing small, waxy, white flowers. Each flower contains anthers, the male organs of the tree, which produce a fine, dust-like pollen. The female part of the flower is called the pistil.
Honey bees and other pollinators move pollen from the anthers to the pistil while collecting nectar from each flower. Sperm cells in the pollen enter the pistil to fertilise ovules in the base of the pistil, called the ovary.
Seeds form from the fertilised ovules. The petals drop and the ovary grows into a seed pod. Inside, the seeds are held in sections with many small cells that contain juice. The outer rind of the citrus fruit protects the seeds.
When ripe, the fruit is typically eaten by animals or humans, which drop the seeds on the ground. The fruit may also just fall to the ground. These seeds then germinate to begin the cycle of life again.