Plants have life cycles that includes germination, growing to maturity and dying. The first plants washed ashore as spores, which survive today as mosses and other bryophytes. Once ashore, they had to develop new ways to breathe and reproduce. The result was the remarkable angiosperm, a group of plants that comprise the majority of plants we know today, including the annual and perennial flowers in our gardens.
Whatever the nature of the beginning of plant life, organisms have developed a huge number of variations on the original mosses. Each plant begins from a seed, a division of an existing plants roots or a cutting of its tissue, or stem. Each method of propagation carries the parent's genetic traits but only a seed provides the potential for plant diversity.
Seeds contain living embryos that grow inside a protective coating until conditions are right to break out and send a shoot to become the plant's roots (radicle) or its first leaves (plumule). The root collects food from the soil and young leaves begin manufacturing chlorophyll, the chemical plants use to process soil nutrients and which gives them their green color. Growth is dependent on physical conditions. Plants that start growing too soon can freeze or dry out and plants that grow where the ground is too warm may succumb to mold.
Eventually, "true leaves" begin to grow. These are the food factories that will nourish the plant as it grows and reproduces. Embryonic leaves wither as adult leaves form and use chloroplasts to produce energy that transforms nutrients into food. The way the plant grows---called its habit---is determined by genetics. But gardeners can force branching. Storms or garden-dwelling rodents can also change the growth pattern. As long as the seedling retains its first few true leaves, however, it will probably survive.
At some point, the plant will mature and begin to produce the "inflorescence," which we call flowers. Some plants, notably perennials like roses and lilies, bloom only during a certain period and others, like many annuals, have a bloom period that may last all season long. Fruits and vegetables flower before "setting" fruit, where the seeds reside until they are mature.
Asexual plants contain both male and female parts. Plants that reproduce sexually depend on fertilization, usually aided by insects that land on flowers and transfer pollen from the anther---the organ on the end of the stamen that produces pollen---to the mouth of the pistil---the channel leading to the plant's ovary. Once the egg in the ovary has been fertilized with pollen, it begins to grow. Once the egg is fertilized (or withers if it escapes pollination) the flower fades; its job of attracting insects is over. Some plants can self-pollinate; their egg will respond to their own pollen. Some plants do not self-pollinate; they must be fertilized with pollen from another plant, making natural hybridization possible.
Dormancy or Death
As the seeds ripen in the seed pod or fruit, the parent plant prepares for dormancy or death. The seeds are carried away by wind, water or animals and the plant top dies back, its work done. Perennial plants will grow again from the same root system but the entire system of an annual plant dies.