Some plants, called annuals, germinate from seed and then flower and die within one year. Winter annuals may germinate in late autumn, live through the winter as slow-growing seedlings under the snow and grow and flower in spring or early summer. Many cereals are winter annuals, but often a single species has winter-annual and spring-annual varieties or agricultural varieties, as is the case with barley, rye, and wheat.
Biennials typically germinate in the spring, grow as a rosette - a circle of leaves close to the ground, as in beets or dandelion - during the first summer and send up a flowering shoot during the second season.
Perennials, which grow and flower for several seasons, are called polycarpic.
Monocarpic plants are those that flower only once and then die. These include annuals and biennials but also a few species such as bamboo and the century plant that grow for several years, flower once and then die.
The variety of flowering plants is enormous. Some angiosperm trees challenge the great conifers in size, while some floating flowering plants are smaller than a fingernail. Orchids grow suspended on the trunks of trees in tropical rain forests and the sausage tree has a huge hanging flower pollinated by bats.
Cacti and yucca plants have needles or swords for protection and some angiosperms trap and consume insects. A few species of flowering plants grow during a short season in Antarctica; others grow near the tops of all but the highest mountains.
Importance of flowers
Flowers and flowering plants form an exceedingly important part of nature. They also provide colour to the surroundings – not only the flowers themselves but also the brilliant coloured leaves that cover the hillsides during the autumn in temperate regions. Gymnosperms, which were predominant until the angiosperms appeared 140 million years ago, have no colourful flowers; a few exhibit autumn colours.
Flowers are used in plantings and in many ceremonies; their seeds, fruits, roots, stems and leaves also provide food, as has been noted in several examples. In turn, most of the animals that humans eat depend upon flowering plants for their food supply.