Horticulture Principles and Practices

2.3 OTHER CLASSIFICATION SYSTEMS (OPERATIONAL)
A number of operational classification systems are employed simultaneously in the field
of horticulture. The following are some of the major systems.
2.3.1 SEASONAL GROWTH CYCLE
Plants may be classified into four general groups based on growth cycle (Figure 2–3).
Growth cycle refers to the period from first establishment (e.g., by seed) to when the
plant dies. The four categories are as follows:
1. Annuals. An annual plant lives through only one growing season, completing
its life cycle (seed, seedling, flowering, fruiting, and death) in that period. This
group includes many weeds, garden flowers, vegetables, and wild flowers. The
duration of a life cycle is variable and may be a few weeks to several months,
depending on the species. Annuals are the basis of a major horticultural
production group called annual bedding plants. These plants are produced
largely for use in the landscape and also the vegetable garden. Popular annual
flowers are geranium (Geranium spp.), zinnia (Zinnia elegans), marigold
(Tagetes spp.), and pansy (Viola tricolor). In cultivation, certain vegetables
such as tomato (Lycopersicon esculentum) are produced on an annual cycle.
2. Biennials. A biennial is a plant that completes its life cycle in two growing
seasons. In the first season, it produces only basal leaves; it grows a stem,
produces flowers and fruits, and dies in the second season. The plant usually
requires some special environmental condition or treatment such as exposure to
a cold temperature (vernalization) to be induced to enter the reproductive phase.
Examples of biennials are sugar beet (Beta vulgaris) and onion (Allium cepa).
Even though annuals and biennials rarely become woody in temperate regions,
these plants may sometimes produce secondary growth in their stems and roots.
3. Perennials. Perennials may be herbaceous or woody. They persist year-round
through the adverse weather of the nongrowing seasons (winter or drought)
and then flower and fruit after a variable number of years of vegetative growth
beyond the second year. Herbaceous perennials survive the unfavorable season
as dormant underground structures (e.g., roots, rhizomes, bulbs, and tubers)
that are modified primary vegetative parts of the plant. Examples of
Annual
A plant that completes its
life cycle in one growing
season or one year.
Biennial
A plant that completes its
life cycle in two cropping
seasons, the first involving
vegetative growth and the
second flowering and
death.
Perennial
A plant that grows year
after year without
replanting.
Death
Seed
Annual
Reproductive
Vegetative
growth
Death
Reproductive
growth
Seed
Biennial
Vegetative
growth 2
Vegetative
growth 1
Dormancy
FIGURE 2–3 Classification of
flowering plants according to the
duration of their growth cycle
from seed to seed. Variations
occur within each category, even
for the same species, due in part
to the activities of plant breeders.
Seed
Seed
Death
Perennial
Vegetative
growth
Death
Monocarp
Vegetative
growth
Dormancy
Reproductive
growth
Reproductive
growth
Dormancy
2.3 Other Classification Systems (Operational) 43