A tree is a plant with an elongated stem, or trunk, supporting branches and leaves in most species. Trees tend to be long-lived, some reaching several thousand years old. Trees have been in existence for 370 million years.
A variety of plant species have independently evolved a woody trunk and branches to compete for sunlight. In more general sense, tall palms, tree ferns, bananas and bamboos are also trees. The roots branch out under the ground to anchor the tree and to extract moisture and nutrients from the soil. Above ground, the branches usually bear leaves, which capture light.
Trees reduce erosion and moderate the climate. Trees and forests provide a habitat for many species of animals and plants. Some trees provide edible fruit.
Seed is an embryonic plant enclosed in a protective outer covering. The formation of the seed is part of the process of reproduction in seed plants. Seeds have been an important development in the reproduction and success of gymnosperms and angiosperms plants, that now dominate biological niches on land.
The term "seed" also has a general meaning of anything that can be sown, e.g. "seed" potatoes (tubers), "seeds" of corn or sunflower "seeds".
Many structures commonly referred to as "seeds" are actually dry fruits. Different groups of plants have other modifications, the so-called stone fruits (such as the peach) have a hardened fruit layer (the endocarp) fused to and surrounding the actual seed.
Nuts are the one-seeded, hard-shelled fruit of some plants with an indehiscent seed (acorn, hazelnut).