A Guide to Wildflower Leaves
Wildflower leaves are an important aid in identifying wildflowers. Each leaf has two main parts: a stalk (unless the leaf is stalkless) and a blade. In examining the leaves, generally there are six characteristics to consider: (1) leaf type, (2) leaf shape, (3) leaf veins, (4) leaf margin (edge), (5) leaf arrangement on the plant stem, and (6) leaf attachment. Keep in mind, however, that there are exceptions to every rule, wildflower leaves notwithstanding. For example, aquatic plants may have leaves that float or are submersed and difficult to observe or discern; other plants may lack leaves altogether at flowering time, but produce leaves when flowering is finished.
1. Leaf Type. Wildflower leaves can be either simple or compound. A simple leaf has only one "blade" that is undivided, although its shape can vary and be affected by lobes.
A compound leaf has a fully subdivided blade (lamina) composed of separate parts called leaflets separated along the leaf's primary or secondary vein. The leaflets of a compound leaf may also be lobed. It can be challenging to determine whether a leaf is simple or compound. Useful clues include the location of the leaf stalk (petiole) on the flower stem and the existence of stipules (leaf-like bracts) or stipule scars at the point of attachment on the stem. Also, branches and stems of plants carry flower and leaf buds, whereas leaves do not. Furthermore, the leaflets of a compound leaf lie in the same plane and the whole leaf forms a flat surface.
A compound leaf may have just three leaflets (trifoliate), or have the leaflets radiating from the end of the leaf stalk like fingers on a hand (palmately compound), or have the leaflets arranged along the leaf's central stalk (pinnately compound).
2. Leaf Shape. Wildflower leaves can vary according to the shape of the leaf. Here we offer eight. Other sources may include additional leaf shapes.
3. Leaf Veins. There are two general types of vein orientation in wildflower
4. Leaf Margin. The leaf margin (leaf edge) is also characteristic in identifying wildflowers. A leaf is entire or smooth-margined if the leaf margin is even and unbroken, without teeth or lobes. A leaf is toothed if the margin has regular, shallow pointed indentations or wavy, scalloped edges. A leaf is lobed if it has one or more deep indentations which do not reach the center of the leaf but, in effect, separate the leaf into sections. A deeply-lobed leaf, where the indentations reach nearly to the main vein, is called cleft. (Note that leaves that are lobed at the base, such as arrow-shaped or heart-shaped leaves, are considered entire or toothed depending on the margins.) A leaf is dissected when it is deeply, sometimes finely, divided into numerous segments.
5. Leaf arrangement on the flower stem. Leaves are arranged on wildflower stems in a variety of ways. Leaves growing at the base of the plant are basal leaves. Leaves growing on the stem above the base are stem leaves. Leaves are alternate when they are attached singularly at nodes, alternating along the stem. Leaves are opposite when they are attached in pairs directly across from each other at each node on the stem. Leaves are whorled when three or more leaves are attached at each point or node on the stem. Leaves are rosulate when they form a rosette or circular cluster around the stem, usually at the base of the plant. Leaves may also be absent from the plant while the plant is in bloom and only appear when the plant has concluded flowering.
6. Leaf attachments. Leaves are attached to wildflower stems in several ways. A leaf with a stalk (petiole) between the blade and the flower stem is a stalked or petioled leaf. The stalk may be relatively long and quite obvious, it could be short, or it could be very short and not obvious. A leaf in which the blade attaches directly to the stem is stalkless or sessile. A leaf is clasping if the blade of the leaf partially or wholly surrounds the flower stem. When the stem appears to pass through the basal margin of the leaf blade itself, the leaves are called perfoliate and in some cases the leaves, when opposite, are united around the stem.
Other criteria may also be applied when identifying leaves, including the leaf color (top and underside), the smoothness or roughness of the leaf surface (top and underside), the presence of a waxy or sticky feel, and other characteristics.
Newcomb's (see Printed References on Home page) suggests that, when identifying leaves, choose the largest or best-developed leaves, usually those closer to the base of the plant, when determining leaf type. Also, if two types of leaves are present on the plant, choose the leaf with the deepest indentation for determining the category in which the leaves should be placed.
(See www.wikipedia.org/wiki/Leaf for an interesting and detailed discussion of leaf anatomy, morphology and terminology.)