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Leaves as plant identifiers
Leaves are useful for plant identification. A leaf's venation (Figure 13), blade and margin shapes (Figures 14 & 15) and apex and base shapes (Figure 16) can be important identifying characteristics.
Leaf type (Figure 17) also is important for identification. There are two types of leaves: simple and compound. In simple leaves, the leaf blade is a single, continuous unit. Compound leaves are composed of several separate leaflets arising from the same petiole. Some leaves are doubly compound. Leaf type can be confusing, because a deeply lobed simple leaf may look like a compound leaf.
Leaf arrangement along a stem also is used in plant identification (Figure 18). There are four types of leaf arrangement:
- Opposite leaves are positioned across the stem from
each other, with two leaves at each node.
Example: http://csdl.tamu.edu/FLORA/tfplab/veg24.jpg - Alternate (spiral) leaves are arranged in alternate
steps along the stem, with only one leaf at each node.
Example: http://csdl.tamu.edu/FLORA/tfplab/veg25.jpg - Whorled leaves are arranged in circles along the stem.
Example: http://csdl.tamu.edu/FLORA/tfplab/veg26.jpg - Rosulate leaves are arranged in a rosette around a stem with extremely short nodes.
Leaves as food
The leaf blade is the principal edible part of several horticultural crops, including chives, collards, dandelions, endives, kale, leaf lettuce, mustard, parsley, spinach, Swiss chard, and other greens. The edible part of leeks, onions, and Florence fennel is a cluster of fleshy leaf bases. The petiole is the edible product in celery and rhubarb.
additional resources
fascicled leaf types/needled evergreens
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http://csdl.tamu.edu/FLORA/tfplab/veg31.jpg
Take the quiz: [Leaves]
