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.
