Discovering the Plant Families: Asteraceae

What do dandelions, lettuce, dahlias and daisies have in common? They all belong to the large Asteraceae family (formerly known as Compositae).

Our journey through the world of botanical families continues today with the Asteraceae, which occupy an important position in terms of the number of species, vying for the coveted podium with the Fabaceae and Orchidaceae. The Asteraceae family includes no fewer than 33,000 species divided into 1,800 genera. Mostly herbaceous, the family includes a few genera of trees, shrubs and vines. Cosmopolitan, the Asteraceae are also present in almost all terrestrial ecosystems, with a high diversity in the Mediterranean region and in temperate zones.

Flowers

Even the novice can easily recognize a plant belonging to the Asteraceae family when strolling through a garden. This is because this family has characteristic flowers, almost all of which resemble daisies. But are they really flowers? Asteraceae actually have clusters of flowers, called inflorescences. There are several types of inflorescences in the plant world. In Asteraceae, these floral clusters (inflorescences) are called capitula. But as always, botany has surprises in store for us. We will discover them later.

When we think we are looking at a daisy, we are in fact looking at several flowers. The “Compositae”, the former name of the Asteraceae family, alludes to these inflorescences composed of several flowers. The etymology of the Asteraceae family refers to the genus Aster, which means star-shaped. But let’s get back to our capitulum. From an evolutionary point of view, this inflorescence is very interesting because it imitates a very large flower. Particularly suitable for pollination, the capitulum represents a veritable landing strip for the pollinating insect, allowing it to feed and to bring significant amounts of pollen.

Let’s take a closer look at this flower, which seems so simple at first glance.

The florets that make up the capitulum usually take two forms:

A tubular form: tube-shaped florets, generally located in the center of the capitulum;

A ligulate form: tongue-shaped florets (or “petals”), arranged around the edge.

Examples of Flowers

Here, simpler forms of flower heads. In the latter, we find tubular florets in the center and ligulate florets on the periphery.

More Complex Forms of Flower Heads (Florets All With Ligules)

Following several selections and hybridizations, certain species have resulted in cultivars with capitula that are all or mostly ligulate.

Spike-Like Capitula

The dense blazing star (Liatris spicata), a perennial well known to horticulturists, bears no resemblance to the flower heads seen previously, and yet it is made up of them. It is in fact several flower heads grouped along a spike-like axis. As we said, botany is full of surprises!

Capitulum Capituli!

And why not finish with the queen of capitula, the inflorescence of the edelweiss (Leontopodium nivale).

Fruit: Achenes

In botanical terms, an achene is a dry, indehiscent fruit containing a single seed, whose pericarp (the envelope) is more or less sclerified and not attached to the seed. To explain what the typical fruit of the Asteraceae is, we could use the sunflower achene as an example. In fact, you could say that the dry fruit is the sunflower achene and that the seed is what is inside. Like sunflowers, Asteraceae all produce achenes, but in a variety of shapes and colors. Here are some achenes:

Leaves and Stems

There are no real characteristics or at least no real common features for the vegetative apparatus of the Asteraceae except that the leaves are always without stipules. Stipules are leaf organs resembling small leaves and located on either side of the leaf petiole.

Some Asteraceae

Do you already have names and images of Asteraceae in mind? Here are a few more!

Ornamental Plants

• Ox-eye daisy (Leucanthemum vulgare)
• Sunflower (Helianthus annuus)
• Dahlia (Dahlia spp.)
• Chrysanthemum (Chrysanthemum spp.)
• Aster (Aster spp.)
• Zinnia (Zinnia spp.)
• Black-eyed-susan (Rudbeckia spp.)
• Blanket flowre (Gaillardia spp.)
• Cosmos (Cosmos spp.)
• Conflower (Echinacea spp.)

Edible Plants

• Lettice (Lactuca sativa)
• Endive/Common chicory (Cichorium endivia, Cichorium intybus)
• Artichoke (Cynara cardunculus var. scolymus)
• Topinambour (Helianthus tuberosus)

Medicinal Plants

• German chamomile (Matricaria chamomilla)
• Roman chamomile (Chamaemelum nobile)
• Tansy (Tanacetum vulgare)
• Yarrow (Achillea millefolium)
• Greater burdock (Arctium lappa)

Plantes d’intérieur

• String-of-pearls’ (Curio rowleyanus)
• String of bananas’ (Curio radicans)
• String of watermelons (Curio herreanus)

Wild and Honey Plants

• Dandelion (Taraxacum officinale)
• Coltsfoot (Tussilago farfara)
• Groundsel (Senecio vulgaris)
• Canada goldenrod (Solidago canadensis)
• Blue wood aster (Symphyotrichum cordifolium)
• Spotted joe-pyeweed (Eutrochium maculatum)

In Summary

To find out if a plant belongs to the Asteraceae family, you will need to observe the presence of more than one of the following criteria:

• Capitulum inflorescence
• Fruit = achene

Although the aster, the eponymous plant of the family, represents an important genus, we now know that it is found alongside an incredible diversity of plants. This wealth of diversity is very valuable for the horticulturist, because all the flowering periods are represented. An abundant botanical family to discover.

Happy observing!

In our next installment… Solanaceae!