Plants have developed physical and chemical defenses to protect themselves from animals. Physical defenses of lants include such structures as spines, thorns, and prickles. Many plants produce sticky, strong-smelling oils to defend themselves. Some plants also protect themselves through the timing of producing flowers and fruits.
Deciduous trees shed all their leaves for a part of the year. They do this annually at the end of the growing season. Many deciduous trees bear flowers and pollinate when they are leafless. Maples or elms are examples of deciduous trees.
Club mosses are small evergreen plants. However, they were as large as trees about 354 million to 290 million years ago. Club mosses are more like ferns than real mosses. They have small, needle-like leaves that are often spirally arranged. They reproduce with the help of spores. There are about 200 species of club mosses.
Annuals are plants that complete their life cycle in one growing season. They typically show rapid growth during the rainy seasons. They quickly flower, produce seeds, and die. The seeds of annuals lie dormant until the next rainy season. Some plants may be summer annuals and winter annuals. Examples of true annuals include lettuce, corn, pea, marigold, cauliflower, and watermelon.
Certain plants release chemicals, which prevent other plants from growing nearby. This is known as allelopathy. Plants that use allelopathy are black walnut trees, some species of pine trees, sunflowers, wormwoods, sagebrushes, and trees of heaven.
Olive trees, which live from 300 to 400 years on average, require much attention. They are grown mainly in Turkey, Greece, Italy, Spain, and North Africa, and, after the sixteenth century, also in North and South America, China and Japan.
