THE HUGE COMPOSITE FAMILY

The Composite Family is likely to be the best represented plant family in your backyard. Here are some of the best-known composites: Chicory, dandelion, chrysanthemum, yarrow, coreopsis, sunflower, Spanish needle, dahlia, zinnia, goldenrod, fleabane, aster, sneezeweed, groundsel, eupatorium, ageratum, lettuce, thistle, ironweed, cosmos, and Black-eyed Susan. L.H. Bailey's Manual of Cultivated Plants, revised edition, lists 101 genera, or kinds, of composite found under cultivation.

Some of those 101 genera are themselves huge. Gray's Manual of Botany, 8th edition, lists for the northeastern U.S. and adjacent Canada 68 species of wild aster, and 75 species of wild goldenrod!

In other words, if you're going to understand all the blossoms you encounter as a backyard naturalist, at some time or another you must come to terms with the composites' very unique flowers.

COMPOSITE FAMILY FLOWER STRUCTURE

As the diagram at the right shows, the amazing thing that composites have done is to miniaturize and simplify each flower, then pack a number of these tiny flowers on their ends next to one another, on a platform called a receptacle, and finally to organize the whole resulting cluster so that the many flowers look like just one flower. In other words the sunflower at the top of this page,  is actually a collection of hundreds of flowers!

Moreover, in that sunflower you are seeing two kinds of flower. The two composite-flower types are usually known as disk flowers and ray flowers, and the differences between these two flower types is shown in the above diagram.  In the picture of the sunflower at the top of this page, the "flower's" broad central area is composed of hundreds of disk flowers, and the yellow "petals" are the ray flowers.

Composite flower heads bear scale-like bracts, which are usually green and overlapping, like the ones at the right. There you see bracts on a Chrysanthemum flower. Bracts are just modified leaves. When you are identifying species in the Composite Family, noticing the bracts is very important. In some species the bracts are very slender and in others very wide, sometimes they are other than green, sometimes they are in just one series with the bracts side-to-side instead of overlapping like those above. The collection of all the bracts considered together is called the involucre. The picture above shows a Chrysanthemum flower's involucre consisting of overlapping involucral bracts.

At the left you see a marigold blossom I just plucked from my garden and broke apart. Notice the difference between the ray and disk flowers, and see how the achenes (fruits, explained below) are neatly stacked atop the low, conical receptacle. The achenes in the middle, at the very top of the receptacle, are white because they are still immature. Later they will turn black.

By the way, notice that at least one flower in the area where disk flowers are supposed to be has a short ray -- is as much ray flower as disc flower. Often you see this, especially in horticultural species. In fact the overall difference in the genetic information used for making disk flowers and information for ray flowers is very slight.

THE THREE KINDS OF COMPOSITE FLOWER

When you begin trying to figure out what kind of composite flower you have, the first thing you should notice is how the heads are configured, in terms of disk and ray flowers. Here are the three basic flower-head strategies:

• Heads composed of only ray flowers, as in dandelion (shown at the right), chicory, endive, and wild lettuce.

• Heads composed of only disk flowers, as in eupatorium (the white flowers at the right), ageratum, thistles, and burdock.

• Heads composed of both disk and ray flowers, with disk flowers tightly packed together in the head's "eye," while enlarged ray flowers function as petals radiating outward from the eye. Species in this group include sunflowers, asters, Black-eyed Susans, chrysanthemums, dahlias, and the red zinnia pictured at the right. In the zinnia, the yellow, five-lobed disk flowers in the head's center are clearly visible, surrounded by red ray flowers, which most people would incorrectly call "petals."

ANALYZING DISK & RAY FLOWER STRUCTURE

Once composite-blossom basics are understood, you should seek out a composite flower, remove a tiny disk or ray flower from the head, and see if you can find the flower's basic parts. If you don't understand terms like style and stamen, you may want to consult our Standard Blossom Page  as you read through the following. Here are a couple of composite-family peculiarities to keep in mind:

• STAMENS: Stamens in disk and ray flowers number four or five, and are fused together by their anthers to form a cylinder around the style.

• PISTILS: In each flower type a thread-like style passes up through the anther-cylinder to two long stigma lobes projecting above the blossom. The ovary is situated below the point of attachment for sepals and petals, not in the center of them as with the Standard Blossom. Technically such an ovary is referred to as being inferior.

Pistils develop into fruits. The Composite Family's inferior ovary transforms into a unique kind of fruit called an achene. In other words, technically speaking, sunflower "seeds" are actually one-seeded fruits of the achene type. Of course in standard English, speaking with people whose minds are on other things than botany, just let people call sunflower fruits "seeds."

PAPPUSES

Atop the achenes of many members of the Composite Family sepals have become reduced to special projections known collectively as the pappus. At the bottom of the picture at the right you see the achene of a Eupatorium plant. Atop the achene, the slender, radiating items are the pappus. Later the pappuses on these mature achenes will serve as parachutes, enabling the achenes to be blown by the wind into new territory. The purple item in the picture's center is the disk flower.

Pappuses come in an amazing variety of forms, not just the hairlike bristles shown at the right.  Below you see achenes of one of several species of "beggar-ticks" or "sticktights," Bidens bipinnata. On these achenes the pappus bristles have stiffened into barbs that can stick into animal fur (or hikers' pants), and thus travel into new territory to be planted.

Echinacea pappuses, as shown in the picture in the next section below, are cup-like crowns. Sunflower pappuses consist of two sharp scales that fall off when the achene is mature. Common thistles have feathery bristles united into a ring at the base. Many flowers have no pappuses at all.

On and on pappus variations go, typically all the members of a genus possessing similar types. Needless to say, when identifying composite blossoms, the pappus is one of the most important features to note.

BOOKS ABOUT COMPOSITES:

BRACTS ON THE RECEPTACLE

If you get serious about identifying the many kinds of composite flowers, inevitably one day as you work through an identification key you'll need to decide whether flowers in the composite head's receptacle are accompanied by bracts. When that time comes you would do well to remember the picture at the right, which shows an Echinacea blossom's disk flower with its very well formed bract. Many composite flowers have no bracts at all, and the vast majority of the ones who do possess bracts have bracts that are much smaller, paler and more inconspicuous than the one at the right. Still, here you can see how at least one kind of composite flower is accompanied by a bract. Notice how the bract is rather scoop-shaped, with the disk flower more or less fitting into its concavity.