Plant Structures and characteristics useful for plant ID


Caladium foliage is very distinct

There are many things that can be used to help you identify a plant and to distinguish between plants. In this lesson we will examine a few of the more useful distinguishing characteristics for herbaceous annuals and perennials


There are numerous distinctive characteristics of flowers that can be used to differentiate between plants. 

Parts of a mature flower. (Drawing from Wikimedia Commons by: Mariana Ruiz)

Flower parts: The flower parts that are most useful in plant ID are the petals and sepals (the Perianth), the stamen and anthers, and the  stigma, style and ovary. 

The number and shape of each is often characteristic of a given plant. For example Isotoma has 5 distinct petals. Hibiscus also has 5 petals but it has a very distinct arrangement of fused stamens and styles. 

Petals can also be fused as in Petunia where the petals are joined together to form a tubular or trumpet shaped structure. 

Hibiscus flower with fused stamens and styles. This flower is very distinct and makes this plant easy to identify when it is in bloom.

Flowers can be single of double. In double flowers reproductive parts have been totally or partially converted into additional petals. 

Flowers can be individual or combined to form an inflorescence as in the Asteraceae

Some flowers like New Guinea Impatiens will have other distinguishing characteristics like long tubular spurs. 

In general the flower is going to be your best identifying characteristic for plants we will study in this class.


Hemerocallis 'Happy Returns

Flower colors: Many plants have distinct flower colors or a limited range of flower colors that can aid in identification. For example, you can distinguish between 2 of the most common re-blooming Hemerocallis cultivars by the flower color. Hemerocallis ‘Stella de Oro’ has a golden yellow color flower while Hemerocallis ‘Happy Returns’ is bright yellow.


Hemerocallis ‘Stella de Oro’ (Golden). These two common daylily cultivars can be easily distinguished by the color of the flowers

Flower period: Another useful characteristic for plant identification is when the plants flower and for how long. For example, Doronicum is a yellow spring blooming plant with daisy like flowers. If you find a fall blooming yellow daisy you will know it is not Doronicum. Aztec (African) marigolds (Tagetes erecta) will generally bloom later than French marigolds (Tagetes patula) or Triploid Hybrids (Aztec and french marigold hybrids).

Flower size: Some species and cultivars can be distinguished from others based on flower size, although breeding can have a big influence on how useful this characteristic can be. For example, you can usually distinguish between a Petunia and a Calibrachoa based on flower size. Petunia flowers are generally much larger than Calibrachoa flowers, however there are some small flowered petunia cultivars and there are petunia and calibrachoa hybrids which blur this distinction.


Calibrachoa can usually be distinguished from petunia based on flower size

Scent: Some plants and flowers have a distinct scent that can be used to identify them. For example, Matthiola incana (Stocks) have a distinctive cinnamon/clove scent.

Arrangement: Flowers may be single in clusters, spikes or other configurations.

Seeds and seed heads:

The structure of seed heads is also frequently an excellent characteristic that can be used to help you identify a plant. 


For example, Iris domestica aka Belamcanda chinensis (Blackberry Lily) has a seed head that looks like a large blackberry, so if you find a lily-like plant with large blackberry-like seed clusters you will know it is Belamcanda. 


Poppies are easily identified by their distinct seed heads 


Ornamental Capsicum is easily distinguished by it’s peppers. 

Seed clusters are often the most reliable way to identify ornamental grasses and identification of some may be quite difficult without flowers or seeds.


There are a number of distinctive leaf characteristics that can be used to identify herbaceous perennials and annuals. Many plants have leaves that clearly identify the plant, with others the leaves may only provide clues that must be combined with flowers to provide a conclusive ID.

Leaf shape: Leaves can take on a wide variety of shapes. Some of the common shapes you should be able to distinguish are linear and lanceolate, ovate, eliptic, whorled, lobed, pinnate, etc. The shape may in some cases be enough to identify the plant.

Margin: In addition to leaf shape the leaf margin is a useful characteristic. Leaves can be entire, serate, lobate, spiny, etc. 

Venation: The direction of the leaf veins is also useful in identifying specific plants. Common pattens include, arcuate dichotomous, palmate, parallel, reticulate and rotate.

Chart of leaf morphology characteristics. From Wikimedia commons. Derivative work done by McSush. Copyright granted under terms of GNU Free Documentation License.

Leaf attachment and order: Leaves can be opposite or alternate. They can be sessile or have a petiole.

Color: Although most leaves are green, there is considerable variation in color that can sometimes be a good identifying characteristic. Some plants and cultivars may have red, purple, gold, bronze, orange or yellow leaves. For example many Heuchera cultivars have been selected for specific leaf color. The leaf veins may also be a different color than the laminar tissue and a leaf may be variegated. Fall color may also be a useful characteristic. For example Amsonia tabernaemontana has bright yellow fall color 

Scent: Leaves may also have a distinct scent when crushed. Thyme or rosemary for example can be identified by the scent of the foliage.


Begonia’s may be mounding, upright, or trailing depending on the species and cultivar

Plant form and habit:

The shape and growth patterns of a plant are also useful in aiding identification. Some forms or habits that you might find useful in identifying herbaceous annuals and perennials include.

Growth form: Common growth forms for herbaceous plants include, upright, mounding, trailing, vining, rosette forming, and groundcovers. Some dieback shrubs or cutback shrubs are usually considered to be herbaceous plants in the landscape. For example, Perovskia which is actually a shrub or sub-shrub is generally cut back each year in this climate. Some other common descriptions we will use in class include, Grass or grass-like, Herb or forb, bulb or bulb-like plant and rhizomatous.

Deciduous vs. evergreen or semi-evergreen: Many herbaceous perennials are evergreen or semi-evergreen. This can be a useful characteristic in identification. For example Asarum canadense is deciduous while it’s European cousin Asarum europaeum is evergreen.

Plant lifecycle: Plants can be annual, completing their lifecycle in a single growing season, biennial, usually going through two seasons to complete the lifecycle, or perennial, living for more than 3 years and usually able to reproduce each season. Lifecycle may be useful in identifying plants but in the landscape we often use tender perennials and biennials as annuals. 

Plant identification keys:

Using these and other descriptive characteristics identification keys have been developed to aid in identifying unknown plant specimens. Many of the tools are now available online. The USDA has developed some experimental Online keys for several types of plants. For example is you want to identify a grass in Pennsylvania you can use the following key

Plant description and identification exercise:

Complete this exercise using the Assignment in Canvas week 2 module

Describe the following plants in terms of the characteristics that will allow you to identify the plant. Include in your description plant form, a description of the foliage, a description of the flowers, and fruit or seeds.

  1. Belamcanda chinensis
  2. Agastache
  3. Lantana camera

Use the USDA Pennsylvania grass key to try to key out one of the grasses in the arboretum

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