LAMIACEAE – The Mint Family

by Adriana Lopez-Villalobos and Amelie Mahrt-Smith

Fans of alternative medicine are likely familiar with the mint family, the Lamiaceae. Many of these plants produce essential oils used to battle ailments or boost the immune system – for example, oil of oregano is a common herbal treatment for sore throats, and peppermint oil has a cooling effect that can alleviate sore muscles. Lamiaceae plants are also widely used to add flavour to dishes and drinks, such as sage and rosemary – both in the genus Salvia. Among the other curious properties of the plants in this genus, Salvia divinorium (sometimes known as sage of the diviners or simply Salvia) is psychoactive and is recreationally smoked, chewed or consumed as a tea to induce hallucinations.

There are a variety of chemical compounds responsible for the different properties of plants in the Lamiaceae family. Within the Nepetoidae subfamily, which contains many of the more familiar Lamiaceae plants, the phenolic compound rosmarinic acid is mainly responsible. It was named after the plant from which it was first isolated, Salvia rosmarinus, also known as rosemary. This acid has shown antiviral, antimicrobial, and antioxidant activities. It has also been reported to deter pests like the tobacco hornworm (Manduca sexta).(4) Plants containing rosmarinic acid are most used to treat inflammation – and advances in molecular genetics help to explain why they are effective. In basic terms, rosmarinic acid stops the production of compounds that initiate inflammatory responses when cells are under stress – for example, from a viral infection. The acid inhibits the genes that tell the cell to make inflammation-inducing compounds and thus eases the symptom.(2)

Unsurprisingly, the Lamiaceae have been used in traditional medicine around the world for generations. The common characteristics of this family may have helped early peoples to recognize that a variety of different species can be used for food and medicine – the resemblance between species is strong, especially as you move from the family to the subfamily or to the genus level. Plants in the mint family usually have simple leaves, and they are always oppositely arranged. The stems are usually four-angled, with the leaves at each node being rotated 90° so that the leaves grow in four directions away from the stem. The flowers, which can be hermaphrodite or functionally female (i.e. The male parts are sterile), usually have five lobes and two ‘lips’ – hence the synonym Labiatae which is sometimes used to describe this family. The plant itself often has dense glands and a strong aroma.(3) Using these characteristics, you can identify common plants in the mint family that may be growing around your neighbourhood!

Glechoma hederacea – Ground Ivy

A native to Europe, G. hederacea is a creeping herb that was brought over deliberately by settlers for medicinal use and food and it quickly invaded the North American lands. It is low to the ground and inconspicuous – it can be recognized by its oppositely arranged, kidney-shaped leaves with blunt teeth, and blue-violet flowers about ½ inches long. It flowers in late spring and early summer, and by this time of year has already set seed. The upper lip of the corolla has three lobes that appear to be three distinct petals; the lower lip has two lobes with spots that are usually purple but occasionally pink or white. It flowers early in spring, and by mid-summer has produced seeds. However, it spreads much more rapidly by producing clones than seed dispersal. It is also suspected to have allelopathic effects, which helps it outcompete other plants and rapidly take over an area.(1)

Glechoma hederacea is a member of the Nepetoideae subfamily, so the presence of rosmarinic acid and other chemical compounds makes it a good contender for medicinal use. It is an effective anti-inflammatory agent and as such has been used against catarrh, the excess buildup of mucus caused by inflammation of the body’s mucus membranes.

Prunella vulgaris – Self-heal

Named for its ubiquitous use in traditional medicine, the selfheal is a Holarctic species – native to the continents of the northern hemisphere. It is also a member of the Nepetoideae subfamily and contains rosmarinic acid as the major phenolic compound. It has been said to treat sore throats, fevers, and accelerate wound healing.(5) Prunella vulgaris has also been shown to have specific activity against herpes simplex virus (HSV). Chemical compounds produced by the plant are shown to be effective at reducing the viral load of cells infected with HSV and has the potential to be used as an antiviral treatment for cold sores.(6)

The leaves are lance-shaped and entire, arranged oppositely as is typical of the Lamiaceae. The flowers are violet or purple and found in short spikes. It flowers from late spring to fall and can be found along roadsides and in waste places throughout Kingston, ON right now!

Because of the widespread medicinal and culinary uses of plants in the Lamiaceae family, European colonists brought many of them around the world with them. In addition to intentional introductions, seeds and fragments of plants can hitchhike along with other biological materials brought by settlers. For example, Lamium amplexicaule, also known as common dead-nettle is one of many members of the Mint family that was introduced to North America from the Old World. This specimen was collected in Kingston by George Lawson in 1859. Lawson was appointed professor of Chemistry and Natural History at Queen’s University in 1858, where he set up a botanical laboratory. He was also a founding member the Botanical Society of Canada, established in 1860. His wife, Mrs. Lawson, was an amateur botanist, and inspired equal privileges for female members of the Society. He was an ambitious man and saw the Botanical Society as a means of encouraging botanical research beyond the British settlements in Canada.(7) Although he only stayed a few years at Queen’s before moving on to Dalhousie University, his legacy remains at Queen’s in the specimens that are kept within the Fowler Herbarium.

References

1. Hutchings, M. J., and E. A. C. Price. 1999. Glechoma hederacea L. (Nepta Glechoma Benth., N. hederacea (L.) Trev.). Journal of Ecology 87:347 – 364.
2. Kim, J., S. Song, I. Lee, Y. Kim, I. Yoo, I. Ryoo, and K. Bae. 2011. Anti-inflammatory activity of constituents from Glechoma hederacea var. longituba. Bioorganic & Medicinal Chemistry Letters 21:3484 – 3487.
3. Kokkini, S., R. Karousou, and E. Hanlidou. 2003. Herbs of the Labiatae. Pages 3082 – 3090 in L. Trugo, and P. M. Finglas, editors. Encyclopedia of Food Sciences and Nutrition (Second Edition). Academic Press.
4. Petersen, M., and M. S. J. Simmonds. 2003. Rosmarinic acid. Phytochemistry 62:347 – 364.
5. Psotoyá, J., M. Kolář, J. Soušek, Z. Švagera, J. Vičar, and J. Ulrichová. 2003. Biological activities of Prunella vulgaris. Phytotherapy Research 17:1082 – 1087.
6. Xu, H., S. H. S. Lee, S. F. Lee, R. L. White, and J. Blay. 1999. Isolation and characterization of an anti-HSV polysaccharide from Prunella vulgaris. Antiviral Research 44: 43 – 54.
7. Zeller, S. Lawson, George. 2003. In Dictionary of Canadian Biography, vol. 12, University of Toronto/Université Laval,– accessed online on July 20th, 2020.  http://www.biographi.ca/en/bio/lawson_george_12E.html.

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.

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.

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.