Tree and shrub identification begins when you assess the different parts of the plant and recognize their specific type, color, shape, and size. When these clues are pieced together, you can properly identify the species of the tree or shrub.
One such clue is the leaf arrangement on the stem, which is formally known as phyllotaxy in botany. There are three basic types of leaf arrangements found in trees and shrubs: alternate, opposite, and whorled.
In an alternate leaf arrangement, there is one leaf per plant node, and they alternate sides.
Examples of trees and shrubs with an alternate leaf arrangement:
- Barberry (Berberis thunbergii)
- Black walnut (Juglans nigra). The black walnut may appear to have an opposite leaf arrangement, but it has compound leaves. The opposite leaflets form the entire true leaf, which alternates on the stem.
- Japanese zelkova (Zelkova serrata)
- Ninebark (Physocarpus opulifolius)
- Smoke bush (Cotinus coggygria)
- Sweetgum (Liquidambar styraciflua)
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Opposite Leaf Arrangement
The second type of leaf arrangement is opposite. On these trees and shrubs, two leaves arise from the same node on opposite sides of the stem.
Examples of trees and shrubs with an opposite leaf arrangement:
- Ash trees (Fraxinus spp.). The ash tree has a compound leaf, which is also composed of leaflets arranged oppositely.
- Fringe tree (Chionanthus virginicus)
- Maple trees (Acer spp.)
- Olive trees (Olea spp.)
- Viburnums (Viburnum spp.)
A sub-opposite arrangement is a condition in which the leaves are not spaced far enough apart to be considered alternate nor are they perfectly opposite one another.
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Whorled Leaf Arrangement
When a tree or shrub has a whorled leaf arrangement, there are at least three leaves at each node. Some can have both opposite and whorled leaves throughout the plant.
Examples of trees and shrubs with a whorled leaf arrangement:
- Blackboard tree (Alstonia scholaris)
- Japanese clethra (Clethra barbinervis)
- Lemonwood ( Pittosporum eugenioides)
- Mountain laurel (Kalmia latifolia)
- Panicle hydrangea (Hydrangea paniculata)
- Redvein enkianthus (Enkianthus campanulatus)
- Southern catalpa (Catalpa bignonioides) (sometimes an opposite leaf arrangement)
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All the leaves arise from the base (crown) of the plant.
Many perennial plants are trimmed back to new basal foliage once the older foliage starts to look tired and worn. Examples of perennials that send up new basal growth later in the growing season are Geranium, Polemonium, and Pulmonaria.
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Leaves are arranged in a dense, radiating cluster. Rosettes usually form near the base of the plant.
Rosettes often referred to as basal rosettes, occur in acaulescent plants, such as the common dandelion (Taraxacum officinalis) in the sunflower/aster family (Asteraceae). Acaulescent plants do have a stem, but the internodes are greatly contracted, and the leaves have an alternate spiral arrangement.
Many biennial plants, such as carrots (Daucus carota) and poison hemlock (Coniummaculatum) in the carrot family (Apiaceae), will produce a basal rosette during the first year of growth, followed by the production of a flowering stem with alternate leaves the second yearContinue to 5 of 5 below.
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Leaves are arranged in two rows on opposite sides of the stem.
Distichous phyllotaxis, also called "two-ranked leaf arrangement" is a special case of either opposite or alternate leaf arrangement where the leaves on a stem are arranged in two vertical columns on opposite sides of the stem.
Examples include various bulbous plants such as Boophone. It also occurs in other plant habits such as those of Gasteria or Aloe seedlings, and also in some mature Aloe species such as Aloe plicatilis.