The Asteraceae Family

by Adriana Lopez-Villalobos and Amelie Mahrt-Smith

The Asteraceae, also known as the aster, daisy, or sunflower family, is the second largest family of flowering plants – and it shows. All over Kingston this week, various Asteraceae species are showing off their unique flowers. The radial petals of Asteraceae heads play tricks on our eyes, making them appear as one big flower. In reality, these heads are made up of many, very small perfect ‘disk flowers’ surrounded by a ring of “ray flowers” (Image 1).

What appears to be petals are individual ray flowers, which sometimes have no reproductive parts.

closeup of an individual flower of Tripleurospermum inodorum
Image 1: A closeup of an individual flower of Tripleurospermum inodorum. Try bringing a magnifying glass out with you to get up close and personal with some Asteraceae flowers!

A common pattern of Asteraceae flower heads is the rows of bracts below the ray flowers. Bracts are modified leaves that resemble sepals and that sit beneath the ray flowers (see Image 2). Perfect flowers would often have only one sepal per petal, but asters can have several layers of bracts. While this is not a foolproof test, this is one of the characteristics that can be used to identify aster flowers.

Modified leaves on a T. inodorum flower head
Image 2: Modified leaves, together called the involucre structures on a T. inodorum flower head are the bracts, forming two distinct rows.

Check out the Asteraceae species that we found decorating Kingston’s green spaces this week!

Looking at the images above you might be wondering:

Are there ray flowers in pineapple weed?

Where are the discs flowers in chicory and dandelion?

Do all aster flowers have disc and ray flowers?

If you had questions like this, you are very observant! Not all the aster flowers have the same structure, so let us consider some of the kinds of composite flower you might encounter.

First, notice how the heads are configured in terms of disc and ray flowers. Usually, you will come across three basic flower-head types:

  1. Heads composed of only ray flowers (also called ligulate flowers), as in dandelion, chicory (“a” and “c” in image above), endive, and wild lettuce.
  2. Heads composed of only disc flowers (also called discoid), as those found in species of the genus Eupatorium, Ageratum, Cirsium (thistles) and Arctium burdock (“e” in image above, also see below).
  3. Heads composed of both disc and ray flowers are called radiate flowers. They have disc flowers tightly packed together in the head’s “eye,” while enlarged ray flowers that function as petals radiating outward from the eye. Species in this group include sunflowers, Black-eyed Susans, chrysanthemums, dahlias. In some flowers of the genus Zinnia, the yellow, five-lobed disc flowers in the head’s center are clearly visible, surrounded by red ray flowers, which most people would incorrectly call “petals.”

We love aster flowers! We decided to change the format of our blog post this week to give you an overview of more than one or two species. Identifying species in the Asteraceae family could turn into a complicated puzzle, and for many botanists, this is what attracts them!

To help us learn the different common species you might observe around Kingston or QUBS, without making it overwhelming, it is important to put them into larger botanical categories. These categories are called subfamilies. The species we have observed over these last weeks, and the ones we are describing in this week’s blog post, fall into three subfamilies: Chicorioideae, Carduoideae and Asteriodeae. Learning the characteristics associated with larger categories (in this case subfamilies) will help you to recognize species out in the field by association – so let’s delve right into it.

Subfamily: Chicorioideae

Commonly known as the chicory subfamily, these plants have no disk flowers, only ray flowers. The rays may overlap all the way to the centre of the flower head. The stems contain a milky juice, which gives them a bitter taste. They are edible and used in folk medicine as a digestive aid, among other uses. All three of the species highlighted here are introduced from Europe. Common species in this family around QUBS land base are: Pilosella aurantiaca (syn =  Hieracium aurantiacum) and Pilosella caespitosa (syn = Hieracium caespitosum). These plants are commonly known as Hawkweed.

a. Taraxacum officinale (common dandelion) 

This abundant weed is familiar to most – the ‘blowballs’ formed by the ripe seeds were bringers of wishes in childhood. The bright yellow flowers, 1-2” wide, crop up from spring until fall on hollow stems. The irregularly lobed leaves are attached at the base. The roots, when roasted, are said to make a flavourful coffee substitute.

b. Tragopogon pratensis (yellow goat’s beard)

The flowers of goat’s beard may resemble dandelion heads on a tall stalk, up to 3 feet high. However, they are only open in the early morning light, hence the alternate common name for this species: Jack-go-to-bed-at-noon. The leaves are grass-like, alternate, and clasp the stem. The leaves are edible, it is slightly bitter, as is the root. The plant is biennial – it takes two years to complete its life cycle, and it turns woody in the second year. The genus name comes from the Greek word tragos. “goat,” and pogon “beard.”

c. Cichorium intybus (chicory)

Part of the endive genus, the chicory plant sports light bluish-purple flowers along its branches. Petals are toothed at the end. The entire plant can reach up to 4 feet (1.2 meters) tall. The leaves are edible, and some species of Cichorium are cultivated for salad greens. Blanching the leaves can reduce their bitter taste. Cichorium is the latinized Arabic name for chicory. The species name intybus comes from the Egiptian word tybi, “January” which is the month in which chicory is traditionally harvested. Common chicory species widely used for food includes the radicchio, puntarelle, and Belgian endive.

Subfamily: Carduoideae

Also known as the thistle or artichoke family. Most of the plants in this group will have some prickly parts, usually the leaves. These are characterized by sharp prickles on their edges, which protects them from herbivores. The plants in this subfamily have their flowerheads protected inside a tight wrapping of bracts, like an artichoke, which by the way belong to the genus Cynara. Cornflowers (Centaurea cyanus) is also a member of this subfamily.

d. Centaurea jacea (brown knapweed)

The brown knapweed is a common ornamental garden species, because its purple, funnel-shaped ray flowers are particularly eye-catching. There are several rows of brownish bracts, which distinguishes it from the black knapweed (characterized by blackish bracts). The petals of the rays attract pollinators like bees, flies, and butterflies and direct them to the disk flowers in the centre. This species was also introduced from Europe.

e. Arctium minus (common burdock)    

Common burdock is introduced across most of North America but this species is native to Europe and Asia. This species is commonly found in many places in Kingston: backyards, parks, waste grounds, rail-way grades and roadside. The taproots and young shoots are edible. The taproots are widely used in herbal medicine and are considered by some to be effective against skin conditions, infections, and in removing heavy metals from the body. The genus Arctium comes from the Greek word arktos, “bear,” a possible reference to the rough-textured bracts. The species name minus means “smaller.”

Subfamily: Asteriodeae

This subfamily is further divided into several tribes (more useful for ID purposes compared to tribes in other subfamilies), one being the Anthemideae (Chamomile) tribe. The plants in this tribe are odorous, and many have been used in traditional medicine (like chamomile tea, a well-known herbal sleep remedy). Another characteristic of this tribe is the bracts, which are thin, dry, and translucent.

f. Matricaria discoidea (pineappleweed)

This wildflower, at first glance, does not look much like its chamomile cousins. It grows low to the ground, with the typical yellow disk flowers in heads but lacking rays. In fact, the species name discoidea, means “without rays, disc-like”. Pineapple weed gets its name from the citrusy smell it gives off when crushed. The fresh plant is edible and makes a nice mild tea that has been used to treat stomach pains, colds, and fevers. This species is native to North America!

g. Achillea millefolium (common yarrow)

It is said that the warrior Achilles used a poultice of yarrow to stop bleeding during battle, which may be where the Achillea genus got its name. It is an astringent, as well as a diuretic and diaphoretic. Yarrow is a North American native, recognizable by small clustered flower heads each with 4-6 rays and several disk flowers in the centre. The petals can be white or pink. The leaves have a lance-shaped outline but are divided into many fine segments.

 

h. Tripleurospermum inodorum (scentless chamomile)

Chamomiles have daisy-like flowers, with white rays and yellow disks. The leaves are finely divided and may be scentless (as in T. inodorum), or strongly scented. It was previously placed in the Matricaria genus with pineapple weed. Despite its name, this species is not one of the commonly used varieties for making chamomile tea.

i. Leucanthemum vulgare (oxeye daisy)

The oxeye daisy bears strong resemblance to the chamomiles; long-stalked white flower heads and yellow disks. They can be differentiated by the leaves, which are slender and toothed as opposed to the finely divided leaves of chamomiles. They also usually bear a single flower head per stalk, whereas chamomiles may have several branches. It is considered an invasive species in parts of North America where it has been introduced.

Also, within the Asteriodeae subfamily is the Astereae tribe, which contains one of our native common North American asters.

j. Erigeron annuus (daisy fleabane)

This daisy-like wildflower is characterized by many rays – usually more than 40. These rays can be white or pinkish. The leaves are distinctively toothed, and the stem is hairy. Daisy fleabane is a pioneer species, which means it is one of the first plants to colonize a new or recently disturbed area. The genus name Erigeron comes from the Greek words eri, “early,” and geron, “old man” a reference to some species flowering and setting fruit early in the growing season.

Asteraceae in the Fowler herbarium.

We have not fully digitized all the cabinets that contain the specimens of this family, however with the incredible work of volunteers Donna and John Greenhorn, undergraduate students Elizabeth Garland (Honours thesis at Dr. Lonnie Aarssen lab 2018), Mahsa Aghaeeaval (SWEP 2019) and Amelie Mahrt-Smith (SWEP 2020), and all the amazing Queen’s volunteers that helped transcribed specimen labels, the database has 374 specimens from more than 30 species. Specimens from Tragopogon, Cirsium, Erigeron, Arctium, Centaurea, Carduus, Grindelia, Bidens, Sonchus, Erechtites and more represent some of the diversity of Asteraceae specimens fully digitized in our collection. Some of the oldest specimens from this family are of Tragopogon pratensis (yellow goat’s beard). We have specimens collected in Kingston since 1831, as part of the original collection of James Fowler. The herbarium also houses specimens across a broad range of localities – Asteraceae species have been collected in eight of the Canadian provinces and five American states. Specimens of bull thistle, Cirsium vulgare, have been donated to the herbarium from Ontario, Quebec, Nova Scotia, New Brunswick, British Columbia, and Alberta! The one below was collected by Queen’s student Annie Boyd in 1897. You will likely see these prickly plants in flower later this summer. Check out the beautifully prepared Erigeron annuus specimen collected in the former Pittsburgh Township, now amalgamated into the city of Kingston (as of January 1, 1998) by Assistant Curator A.E. Garwood. He was a self-taught botanist and naturalist, accountant by profession, and a key member and one of the most prolific contributors of the Fowler herbarium during the 90’s. He worked closely with curators Ronald Beschel and Adele Crowder, and other important collectors such as, C.H. Zavitz, S. VanderKloet, R. Hainault, Good M., and Ian Macdonald. Look at the T. pratensis specimen collected by Ian Macdonald and note the differences on the amount and quality of information included on the labels. What do you observe? Can you draw any conclusions regarding the collection methods, the mounting of specimens and the value of data?

References:

  • Elpel, T.J. 2004. Botany in a Day: The patterns method of plant identification. An herbal field guide to plant families of North America. HOPS Press, LLC, 6th edition. Pp 163-174.
  • Dickinson R. and Royer F. 2014. Plants of Southern Ontario: trees, shrubs wildflowers, grasses, ferns, and aquatic plants. Lone Pine Publishing. Pp 370 – 409 year
  • Niering W and N. Olmstead. 2001. National Audubon Society. Field Guide to Wildflowers. Eastern Region. Revised by Thieret W. John. Chanticleer Press, Inc.
  • Peterson Lee. Field guide to edible wild plants of eastern and central North America. Houghton Mifflin company, Boston NY.
  • Newcomb, L. 1977. Newcomb’s Wildflower Guide. Little, Brown and Company. New York.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s