Focus On Flowers

Biologically speaking, flower parts are all about reproduction. A flower’s showy, colorful petals are designed to attract pollinators such as insects, birds, and even bats. The grouping of petals together is called the corolla. Around the outside of the corolla are sepals, leaflike structures that enclose the flower before it opens. Sepals are often green, but they can also be so colorful that they are mistaken for petals. The grouping of sepals together is called the calyx.

Most flowers include both “male” (staminate) and “female” (pistillate) parts. The stamen, or male flower part, consists of a thin stalk called a filament, topped by an anther, the pollen-bearing structure of the flower. The pistil, or female flower part, is an upright structure in the center of the flower that consists of one or more styles, which are tubelike stalks. The style supports the stigma, the part of the pistil that receives the pollen. Once pollen is deposited on the stigma, it travels down the style to the ovary at the bottom of the pistil. The ovary contains a number of ovules that, when fertilized by pollen, develop into seeds.

Examples Of Inflorescence Types

A plant’s flowering structure can take many forms. Recognizing them is essential for proper plant identification.

A plant’s flowering structure can take many forms.

Although most flowers have both male and female parts, single-sex plants are not uncommon. Technically known as dioecious plants, these bear male and female flower parts on separate plants, which means that both male and female plants must be present for pollination to occur. Dioecious herbs include ginkgo (Ginkgo biloba) and nettle (Urtica dioica). Single-sex flowers are called imperfect flowers; flowers that have both male and female parts are called perfect flowers.

In terms of plant identification, flowers are the most important part of a plant. When identifying a plant, begin by determining how many petals and sepals the flower has. Depending on the flower, this can be straightforward or tricky. Petals can be fused (joined together) or free. Flowers can be regular (symmetrical, with all petals the same size and shape, such as a mustard or rose family flower) or irregular (with some petals different from the others, as in a mint or pea flower). The color of the flower can provide some help, but flower color can be highly variable within a single species, making it an undependable characteristic for identification.

Inside a Composite Flower

Plants in the daisy family (Asteraceae), including purple coneflower, have composite flowers; each is composed of hundreds of tiny flowers.

Plants in the daisy family (Asteraceae), including purple coneflower, have composite flowers; each is composed of hundreds of tiny flowers.

The aster family (Asteraceae) is one of the two largest flowering plant families. (The other is the orchid family, Orchidaceae.) The aster family’s daisylike flowers—called composite flowers—are unique in the plant world. Learning to recognize the basic characteristics of this kind of flower makes it easy to quickly rule out other possibilities when trying to identify a plant.

The sunflower, which is a typical composite flower, is not a single big flower but instead is made up of hundreds of tiny flowers; this is called a composite flower head. A typical composite flower head is composed of numerous ray and disk flowers. Ray flowers are longer, strap-shaped flowers that circle the edge of a flower head. Disk flowers are short, bristly flowers in the center of a flower head.

Leaf Complexity

Learning the kinds of leaf complexity can help you identify the plant.

Learning the kinds of leaf complexity can help you identify the plant.

Sunflower plants have both ray and disk flowers, as do feverfew and echinacea plants. Some composite flower heads, however, are composed solely of either ray or disk flowers. For example, dandelion and chicory flower heads are made up of ray flowers only. Pineapple weed (Matricaria matricarioides), a close relative of German chamomile (M. recutita), has only disk flowers. The arrangement of flowers on a plant’s stem determines its type of inflorescence (flower cluster). This is another important identification feature.