Leaf arrangement, how leaves are attached to their stems, is an important part of plant identification and classification. When “keying” a plant to further identify it, leaf arrangement is one of the early stages. Below are listed the main type of leaf arrangement that you may be asked to verify when identifying any plant.
“Different terms are usually used to describe leaf placement (phyllotaxis):
- Alternate – leaf attachments are singular at nodes, and leaves alternate direction, to a greater or lesser degree, along the stem.
- Opposite – Two structures, one on each opposite side of the stem, typically leaves, branches, or flower parts. Leaf attachments are paired at each node and decussate if, as typical, each successive pair is rotated 90° progressing along the stem.
- Whorled – three or more leaves attach at each point or node on the stem. As with opposite leaves, successive whorls may or may not be decussate, rotated by half the angle between the leaves in the whorl (i.e., successive whorls of three rotated 60°, whorls of four rotated 45°, etc.). Opposite leaves may appear whorled near the tip of the stem.
- Rosulate – leaves form a rosette
Rows – The term “distichous” literally means “2 rows”. Leaves in this arrangement may be alternate or opposite in their attachment. The term “2-ranked” is equivalent. The terms tristichous and tetrastichous are sometimes encountered. For example, the “leaves” (actually microphylls) of most species of Selaginella are tetrastichous, but not decussate.” — Wikipedia.org
More information on leaf arrangement:
- Leaf arrangemet at Wikipedia
- Leaf arrangement at Virtual Herbarium
- Leaf arrangement PDF at the University of Kentucky
Previously on Garden Vocabulary:
- Nitrogen Fixaton
This Garden Vocabulary series seeks to introduce and explain to you — and in many cases, myself — words and terms associated with gardening. Please let me know if there are any terms you would like me to explore. You can leave your ideas in the comments section and we can learn together!