Family Asteraceae :

the Composites

          The Asteraceae family is more commonly known as the Composite, or in Latin Compositae. Composites make up one of the largest flowering plant families with over 25,000 species, considered one of the newest, and perhaps the family whose members are most often found in flower gardens 1. The family is able to survive a wide range of habitats, from the dessert cactus flowers to the aquatic sea aster, though they are not found under water 2. They grow best in sunlit places and in subtropical temperatures. Composites make up a great portion of the flowers in a tall-grass prairie as well as providing it with wide variety of colors blooming through the summer into early fall. Their form is variable as well; Composites are found as shrubs, edible herbs, cacti, weeds and more 1.

The single most important characteristic, which is the family’s namesake, is that what most people consider the flower is actually composed of several small flowers. In fact there are two types of flowers that the flower-head may be composed of, a disk flower or a ray flower. Both are tube-like in form and each has several tiny sepals (also called pappuses), or green petal-looking structures, that enclose the flower in the receptacle. As the name infers, the receptacle is where the many flowers are received or collected into a common structure 5. The shape of the sepals can be a distinguishing feature of a species, as they can be cup-shaped, smooth, thread-like, bristly, or in some occasions, absent 5.

The disk flowers, small and many, are most often found in the center of the receptacle and are symmetrical in appearance and have five lobes. The disk flowers which make up the “eye” of a daisy often contain both male and female reproductive structures. Having both male and female reproductive structures on the same plant makes the Composite family monoceous. There are normally five anthers, part of the male reproductive structure, all gathered to form a tube 4. Butterflies and other insects pollinate the flowers of the Composite family, fertilizing the ovary to form a seed 6. The seed of a disk flower is beneath each flower and enclosed in the hard, dry fruit known as an achene 3. The seeds are distributed by wind dispersal due to the sepals (pappuses) elongating to form a silky parachute following the maturation of the seed 5.

The ray flowers, which are usually infertile, are tube-like where they attach to the receptacle but extend to have the appearance of a petal. They have the most variety of color and range in numbers as well. The ray flowers make up the “petals” that surround the eye of disk flowers. The seed of the ray flower is also inferior. For example, the sunflower seed 5. Although the claim is just two types of flowers, a third type is often seen in horticultural species 5. This third kind is often found in the eye of the flower-head where disk flowers normally reside and is much like a disk flower; however it has a short ray which makes it neither a disk nor a ray flower, but both 5. The flower-heads, composed of disk and/or ray flowers, often attach directly to the stem leaving nearly no stock.

Taking into consideration only the two accepted types of flowers, a Composite flower can have three difference flower-head structures, combination, disk only, and ray only 5. A combination flower, such as a sunflower or a coneflower, is composed of both disk flowers, making up the central eye and ray flowers acting as the petals, as previously described 5. The disk only flower-heads are compiled solely of disk flowers. Thistle flowers are a good example of disk only structures 5. Finally, the ray only structures are exclusively made up of ray flowers as found on a dandelion 5. Therefore, ray flowers of a dandelion are not sterile, as they are in most composite flowers, otherwise they could not reproduce, and we all know they do!

The arrangement of leaves is not a universal feature of the Composite family as they can be in a variety of forms including basal, entire, toothed, alternate, opposite, or compound 3. Basal leaves can be found on a dandelion, growing at the base of the plant where it meets the soil.  Entire leaves have smooth edges while others are toothed. Alternate leaves, as the name suggests, alternate sides and heights up the stem, whereas leaves arranged directly across from each other are called opposite. Several leaflets growing on a single petiole (leaf stem) are known as compound leaves. Though not helpful in distinguishing the plant as a member of the Composite family, the form and arrangement of the leaves can be helpful in identifying the species.

        
    Basal                            Alternate               Opposite                                  Compound
 

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Common Garden Composites          Wild & Weed Composites          Edible Composites
 


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