Horticulture Principles and Practices

2. Shrubs. A shrub has no main trunk. Branches arise from the ground level on a
shrub (Figure 2–5). It is woody and has secondary tissue. Shrubs are perennials
and usually smaller than trees. Examples of shrubs are dogwood (Cornus spp.),
kalmia (Kalmia spp.), and azalea (Rhododendron spp.).
3. Trees. Trees are large plants characterized by one main trunk (Figure 2–6). They
branch on the upper part of the plant, are woody, and have secondary tissue.
Examples include pine (Pinus spp.), oak (Quercus spp.), cedar (Cedrus spp.), and
orange (Citrus sinensis).
2.3.3 COMMON STEM GROWTH FORMS
The criterion for classification is how the stem stands in relation to the ground (Figure 2–7).
There are several types of stem growth forms, the most common ones including the
following:
1. Erect. A stem is erect if, without artificial support, it stands upright (stands at a
90-degree angle to the ground level). Because of the effect of strong winds and other
environmental factors, an erect plant may incline slightly. Trees have erect stems.
To adapt crop plants to mechanized harvesting, plant breeders have developed what
are called “bush” cultivars. These plants have strong stems and stiff branches.
2. Decumbent. The stems of decumbent plants are extremely inclined, with the tips
raised. An example is the peanut (Arachis hypogaea).
3. Creeping (or repent). A plant is described as creeping when it crawls on the
ground, producing adventitious roots at specific points on the stem. Stems that
grow horizontally in this fashion are called stolons. The strawberry plant
(Fragaria spp.) has creeping stems.
4. Climbing. Climbers are vines that, without additional support, will creep on the
ground. There are three general modes of climbing (Figure 2–8). Twiners are
Erect
Creeping
Decumbent
Declined
FIGURE 2–6 A typical tree showing a welldefined,
woody central axis. Certain species produce
or can be manipulated to produce several
stems. (Source: George Acquaah)
FIGURE 2–7 Examples of the variations in the direction
or method of stem growth.
2.3 Other Classification Systems (Operational) 45