GEOG/ES&P 330

California Ecosystems

Stems and Leaf Attachments

Familiarity with the ways leaves attach to stems and the general nature of stems is critical for use of a key to identify plants. In what follows, I'll provide an illustration of a leaf term from the Calphotos web site.

Leaf arrangement or phyllotaxis

Leaves can be arranged along a stem in different ways:

An alternate arrangement means the leaves come out of a node on the stem singly, first on one side of the stem and then the next leaf on the alternate side. Examples:

• Ribes speciosum or fuschia-flowered gooseberry
• Artemisia douglasiana or California mugwort
• Rhus integrifolia or lemonadeberry

An opposite arrangement means that two leaves come out of a single node on the stem, emerging on opposite sides. Examples:

• Salvia leucophylla or purple sage
• Diplacus aurantiacus or sticky monkeyflower
• Symphocarpus mollis or creeping snowberry
• A special variant on this theme is a 4-ranked opposite arrangement, aka decussate: The leaf pairs are on opposite sides of the same node, but each node is at right angles from the ones above and below it. An example is Ambrosia psilostachya or Western ragweed.

A whorled arrangement occurs when more than two leaves come out of a common node, often giving a fascicled or bunched look. Examples:

• Asclepias fascicularis or narrow-leav milkweed
• Eriogonum fasciculatum California buckwheat

Stems

Stems can be described in terms of their relationship to leaves:

• Caulescent: leaves are placed along stems, as in Heteromeles arbutifolia or toyon
• Acaulescent: leaves are basal, rather than along a stem. Stems are bare, bearing only flowers. Example: Duddleya virens or bright green Duddleya

Stems can be characterized in terms of the angles they form with the ground:

• Strict or erect stems are upright, roughly 90° from the ground. Example: Erigeron canadensis or horseweed
• Ascending comes out of the ground at an angle and then grows straight up. Example: Asclepias fascicularis or narrow-leaf milkweed
• Decumbent trails along the ground for a bit and then curls upward. Example: Eriogonum cinereum or ashy-leaf buckwheat
• Prostrate trails along the ground and stays horizontal. Example: Cucurbita palmata or coyote gourd
• Stolons are specialized stems that trail along the ground and stay horizontal, but then start rooting themselves to the ground at the nodes along the stems, and these rooted nodes can become independent individuals if something happened to sever the ground-hugging stem. Example: Fragaria chiloensis or beach strawberry
• Runners are very slender stolons which only form rooting nodes at the end. Example: Chlorophytum comosum or spider plants

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Document maintained by Dr. Rodrigue
First placed on web: 01/30/17
Last revision: 09/13/21