The black eyed susans

Rudbeckia — hirta and laciniata

Rudbeckia hirta

Black-eyed susan (Rudbeckia hirta) is such a popular wildflower it has been added to many cultivated flower gardens. This post compares the Black-eyed susan with another coneflower commonly called Tall coneflower, Green-headed coneflower, or Cutleaf coneflower (Rudbeckia laciniata).

Have you ever looked closely at Black-eyed susan’s leaves? The lower leaves are broadly ovate with palmate veins running the length of the leaf. The leaf margins are roundly toothed.

Rudbeckia hirta

As the plant grows taller, its leaves become more lanceolate with more sharply toothed margins . . .

Rudbeckia hirta

The photo above shows these lance-shaped leaves as well as some unopened flower heads. Watch how the Black-eyed susan’s inflorescence opens . . .

Rudbeckia hirta

The outer ray flowers of this composite flower open first. Then, the inner disk flowers begin opening until we see the full inflorescence blooming.

Rudbeckia hirta

Black-eyed susan is one of many flowers with the common name of “coneflower.” You can see the center disk looks like a dark brown cone. After the seeds mature, the head of the flower (the cone) remains to stand through most of the winter season.

Rudbeckia hirta

Let’s look at another coneflower. As mentioned above, it has several common names alluding to the shape and color of its flower head and its leaves.

Rudbeckia laciniata

This is Tall coneflower (Rudbeckia laciniata). Its lower leaves are also broadly ovate, with palmate venation and rounded toothy margins. As this plant grows taller, its leaves change in shape, just as the Black-eyed susan’s leaves change. In fact, sometimes the Tall coneflower leaf looks divided into three or five (possibly seven?) leaflets. These compound leaves give the impression of being “cut” — which explains the “Cutleaf coneflower” common name along with the “laciniata” scientific name. The petiole of these larger leaves is somewhat grooved.

Rudbeckia laciniata

Tall coneflower can grow very . . . well . . . TALL (up to ten feet). This next photo illustrates some Tall coneflower plants which have fallen over with the weight of their leaves and blossoms. Note the varying leaf shapes.

Rudbeckia laciniata

The leaves near the top of the plant are more lanceolate — just like the Black-eyed susan’s upper leaves.

Rudbeckia laciniata

The leaf margins are also more sharply toothed than the lower leaves.

Rudbeckia laciniata

The above photo shows the composite flower’s ray flowers just beginning to unfold — in a manner quite similar to the Black-eyed susan.

Rudbeckia laciniata

Now we can see why this plant is also called Green-headed coneflower. Its center disk remains green — even as its seeds begin to mature.

Rudbeckia laciniata

This last photo shows the Tall coneflower’s dried seed heads. You can see the lengthy cone as well as how the seeds have fallen away from a large part of the receptacle of one of the heads.

Rudbeckia laciniata

The Friends of the Wild Flower Garden, Inc.

Black-eyed Susan is a coneflower, named for the central blackish-brown disc cone. Plants can be a short lived perennial, a biennial, or an annual. The text here describes var. pulcherrima, the variety native to Minnesota, which grows as a biennial or a perennial.

Stems grow erect to 3 feet high, are green, some with purplish spotting, and quite hairy, sparingly branched, if at all, above mid-stem height, but there may be multiple stems from the root crown.

Leaves: The more basal leaves are lance-like in shape, up to 1 inch wide and 3 to 5 times as long and stalked. Basal leaves usually wither away at flowering time. The stem leaves are more broadly linear or spatula shaped, alternate, may have slight teeth or are entire, but are rough on both sides with white bristly hair; the leaf margin and the underside veins with longer hair. The upper surface is a medium to dark green with a much paler underside. They may have short stalks lower on the stem and become stalkless toward the top of the stem.

The floral array is a solitary long-stalked flower head, the stalk frequently 1/3 the total plant height.

The flowers have heads 2 to 4 inches wide with a central slightly flattened domed disc 1/2 to 3/4 inch wide that is composed of numerous disc florets which are the fertile florets. These have tubular corollas that are yellow-green at the base but brownish-purple at the top where the five lobes of the corolla have rounded to pointed tips. The two branches of the single style have pointed tips. Five stamens surround the style. Disc florets open from the outer perimeter to the center. The yellow ray florets around the perimeter are sterile and will number 8 to 21. These sometimes have a maroon splotch at the base of the ray and tips have 2 to 3 small teeth. Around the outside of the flower head are 2 series of green phyllaries that are linear in shape, quite long, and like the flower stalk are very hairy. The outer ones reflex while the shorter inner ones simply spread.

Seed: Fertile disc florets form a dry black seed (a cypsela), 1.5–2.7 mm long, that does not have any fluffy pappus attached. Seeds are dispersed simply by wind shaking the stem. Seeds require 30 days of cold stratification for germination.

Varieties: Four are currently recognized: Two – var. angustifolia and var floridana – where the stem branches at the base or in the lower stem – these are mostly found along the Gulf Coast. The other two are where any branching that occurs, happens in the upper stem – var. hirta where the basal leaf blades are about 2x as long as the width and the margins are toothed – and var. pulcherrima where the basal leaf blades are 3 to 5x as long as the width and the margins are entire. This is the variety native to Minnesota.

Habitat: Black-eyed Susan is the first coneflower to seasonally bloom in the Upland Garden where bloom can continue until frost. It grows from a tap-rooted root system in sandy to loamy soils; moisture requirements are quite tolerant – wet-mesic to dry; full sun for best bloom, weaker stem plants in partial sun. Reproduction is entirely by re-seeding.

Names: The scientific name is sometimes found with numerous variant listings such as R. hirta L. var. serotina. All have recently been consolidated into the four Rudbeckia hirta series as outlined in Flora of North America (Ref.#W7) and summarized above. The genus name, Rudbeckia, is named after the Swedish father and son, O. J. and O. O. Rudbeck, who were professors of botany and predecessors of Linnaeus. The species, hirta, refers to the roughness of the hair on the leaves and stem. The author name for the plant classification, ‘L.’, refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy.

Comparisons: R. hirta, being so geographically widespread, has many variations in the amount of hair and the color of the ray flowers, depending on local ecotypes. Many native plant nurseries also sell a similar plant – Orange Coneflower – Rudbeckia fulgida, which has a shorter stature, spreading stem branches and a root system with stolons allowing it to spread vegetatively. The native plant market also offers a longer lived version known as Sweet Black-eyed Susan, Rudbeckia subtomentosa. It grows taller, has more flower heads in panicle arrays, larger leaves with 3 to 5 lobes, and has much shorter rough hair on stem and leaves. Then there is the Thin-leaved Coneflower, R. triloba, where the stem leaves are ‘thin’, ovate to elliptic, with 3 to 5 lobes. Photos of all three below.

Annual Black-Eyed Susan, Gloriosa Daisy

The black-eyed Susan is a widespread native of the prairie states, and has become a horticultural delight. The name “gloriosa daisy” has been applied to the multitude of varieties that have grown out of this prairie weed. Although they’re short-lived perennials, they’ll bloom the first year and are often grown as annuals.

Annual Flowers Image Gallery

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Description of black-eyed Susan: Varieties of black-eyed Susan grow from 1 to 3 feet tall and are relatively erect. The flowers are available in many warm-toned colors: yellow, gold, orange, russet, and mahogany. Many of them have bands of color intermixed. The single varieties all have a large black or brown center, contrasting with the color surrounding it. Double flowers may reach 6 inches in diameter.

Growing black-eyed Susan: Bright sun is the gloriosa daisy’s main requirement. It will tolerate poor soil and erratic watering, although it does flourish with better care. Transplant it into the garden in the spring after the last frost. Space plants 10 to 15 inches apart. The taller varieties may need protection from strong winds or staking to keep them from toppling. Cutting the flowers encourages increased blooming.

Propagating black-eyed Susan: By seed. Treated as biennials or perennials, the seeds can be sown in the garden the preceding summer or fall. For bloom the same season, start seeds indoors 8 to 10 weeks prior to transplanting. Seeds germinate in 5 to 10 days at 70 to 75 degrees Fahrenheit.

Uses for black-eyed Susan: Any sunny location is ideal. Beds, borders, and planting strips will benefit from them. Plant them with ornamental grasses. They’ll do well in large containers and are good cut flowers.

Black-eyed Susan related varieties: Cherokee Sunset, an All-America Selections winner, is a mix of yellow, orange, and red doubles. Prairie Sun, also an All-America Selections winner, is a bicolor orange with primrose yellow tips. Rustic Colors is composed of many gold, bronze, and mahogany shades. Irish Eyes has golden flowers with green eyes. Autumn Colors strain has huge flowers in shades of yellow, orange, and red.

Scientific name of black-eyed Susan: Rudbeckia hirta

I’ve been fortunate to travel across most of the United States from coast to coast. The majority of this traveling has been in line with the “Will Work for Food” variety rather than the five-star hotel kind.

I dig this kind of rough and tumble adventure, partly because so much of it is spent outdoors, leaving me exposed to the elements. Folks who travel this way have their tricks for staying sane and keeping a good spirit.

Me? I looked for familiar faces, but not in the people passing by. My eyes were peeled, scanning the roadsides and the fields, the highway medians and the drainage ditches, searching for flowers and plants that I could identify.

The closest companion I had in these journeys was that lovely lady, Black-Eyed Susan.

For so many gardeners and folks who enjoy the outdoors, the sight of Rudbeckia hirta is a familiar and warming one.

That bumblebee yellow with its iconic brown or black center is as American as apple pie. It’s the first flower I learned the name of, and I think I share that with many other gardeners.

Let’s take a look at what makes ol’ Rudbeckia the gem that it is, learn about what it takes to grow these beauties (hint: it doesn’t take much), and get some ideas about varieties we should consider adding to our gardens.

Rudbeckia Hirta

Lest you think poor R. hirta got in a bar fight and wound up with a contusion to her ocular space, let’s set the record straight:

Black-eyed susan is named not because of a propensity to fight other plants, but because of her dark central cone that is surrounded by brightly colored, petal-like rays.

Growing coast to coast in the United States, these perennial flowering plants are known by names like Yellow Ox-Eye Daisy, Brown Betty, Yellow Daisy, and my all-time favorite, Poor Land Daisy.

The flowers are native to the Central and Eastern regions of North America, and have become naturalized in the Western regions and also in China.

Part of their widespread distribution is due to their eagerness to spring up from seed, but their iconic appeal doesn’t hurt either. Throw in their willingness to grow just about anywhere there’s sunshine and a checklist of beneficial aspects, and you’ve got a nice plant for any landscape.

With a Nod to Maryland

Like any good gardening feature, a dash of history goes into this article.

The state flower of Maryland, black-eyed susan has a mounding habit, growing to 2 to 3 feet tall, and can be annual, perennial, or biennial, depending on the variety and where it is grown.

Fans of the University of Southern Mississippi will be delighted to know that this flower was the inspiration for their school colors.

Rudbeckia was given its name as a homage to Swiss botanist Olaus Rudbeck. This guy deserved to at least have a flower named after him; when his home was burning down in 1702, the 71-year-old was standing on the rooftop of a nearby building, shouting orders to the town citizens extinguishing the flames.

The origin of its common name is a trickier subject. Most folks seem to attribute its moniker to a poem by John Gay called “Black-Eyed Susan.” Common names can be an iffy subject, which is why the botanical (Latin) names are always preferred by professionals.

But, just between you and me, I’m a sucker for a bit of mystery and romance, and use common names quite often. I’d rather imagine poetry and folksy tales than strict Latin names any day… but I digress.

Put That Flower to Use

The flowers of the black-eyed susan, which occur singly atop the tall stems, make attractive additions to cut flower arrangements, with a “vase life” of six to 10 days. This earns them a place in any flower garden next to zinnias, gerber daisies, and stock.

In my home we love fresh herbs and cut flowers, and because many cultivars of each thrive in the same conditions, we like to plant a combined herb and flower garden.

It’s a good use of your space, if you’ve got it!

The poor land daisy has also been used medicinally for a long time. The roots have been boiled and strained to aid in treating colds and intestinal worms (yuck), while the dried flowers can be used in much the same way. The flowers can be used in a tincture (basically high-proof alcohol with herbs soaked in it) to reduce swelling.

Not Just For People

Of course, like so many of Mother Nature’s gifts, this species offers other colorful options if yellow isn’t your thing — you’ll find varieties that offer red, orange, and golden petals, as well. All — well, almost all — have the characteristic dark-brown/black centers.

Photo by Matt Suwak.

The flower has long-lasting appeal and simple style. It blooms during the summer and can stretch its golden foliage into late fall in a good year. The seed heads make for attractive winter interest – if you don’t mind the flower going to seed, as they love to do.

And just as humans enjoy the beautiful, bold flowers, butterflies, bees, and other beneficial insects are also attracted to R. hirta.

The flowers are basically giant bullseyes for native pollinators, and this is part of their appeal to wildlife. A tremendous number of flies, bees, wasps, and other critters love to pollinate black-eyed susans.

The leaves even provide the sole food source for the eggs of the silvery checkerspot butterfly, and can be an emergency food source for other animals.

Birds like goldfinches swarm over the seed heads and eat up whatever they can. You’ll also spot sparrows, cardinals, nuthatches, and my personal favorite, the chickadee, devouring these seeds.

The poor land daisy is of vital importance to local environments and is an absolute necessity in any pollinator garden.

If stretches of your property that fit the minimal needs of this flower are available for planting, then give it a shot en masse. The plant spreads easily from seed and needs little care, and your local wildlife will appreciate your caring concern for their well-being.

Growing a Masterpiece

I really do think the black-eyed susan is a masterpiece in flower design. It’s a tough, attractive, long-lasting bloomer with iconic appeal.

The beneficial role it plays in the local environment is multiplied via its eagerness to grow and spread. It’s worth its weight in gold, far as I’m concerned.

Photo by Matt Suwak.

The only major requirement for growing a brown betty is that it has plenty of sunlight. Some species can tolerate a few hours of shade, but these flowers are at their happiest and healthiest when they’re in full-sun conditions.

Take note that these flowers don’t do well in containers. A thriving root system typically reaches depths of six feet or more, and they are far happier when in the ground than in almost any container.

A Good Foundation

Tolerant of many soil types as well, the only time the poor land daisy might suffer is in very poor soil. They thrive in areas with more organic material, in conditions that are moist and well-drained.

When you consider the native habitat of a meadow, it’s easy easy to understand their desire for plenty of organic material and a lack of wet feet.

Rudbeckia can even tolerate some clay-heavy soils, but prefer a neutral pH level. They can survive for several weeks in a dry spell but will ultimatey need to drink up as soon as they are able to.

Many gardeners find this plant to be quite resilient and able to be grown in most any condition, including salty soils, making them a good addition to coastal landscapes.

I’ve seen these flowers planted in many soil conditions in gardens and borders. They seem to do their best when they’re left alone and not fussed over too much.

I favor the properties where the seeds are free to go wild, but not every homeowner sees an informally planted swath of black-eyed susans as desirable.

But I Like a Neat Garden!

It’s still possible to enjoy this plant, and curb it to your liking, if you must.

In this case, gardeners will want to remove the seed heads before the flowers dry completely in late summer or fall. This removes a food source for birds, but some folks really like a tidy garden.

Likewise, for the longer-living perennial varieties, a root division every 3 to 5 years is recommended.

For a more compact, bushier plant, pinch back about five or six inches of growth when the plant reaches a height of one foot. The plant will be a bit more restrained in its height as a result. I find this to be unnecessary, and really enjoy watching the full height flowers dancing in the wind.

I tend to leave my perennials standing over the winter for a variety of reasons, and black-eyed susans respond well to this kind of treatment. Besides, the birds really do appreciate the seeds and I like seeing the snow-capped seed heads!

Quite the Popular Perennial

Companion plants for this garden favorite are almost too many to list, but a few ready and reliable choices include zinnias, globe thistle, sedum, perennial hibiscus, echinacea, joe pye weed, and ornamental grasses.

The yellow and golden colors look nice near shrubs with darker foliage, like smokebush and elderberry.

Photo by Matt Suwak.

Black-eyed susans look great mixed in freely with other flowers, too. That’s why they’re a major component in most wildflower seed mixtures. Don’t worry about placing them perfectly when they’re happy to be tossed out randomly and mixed in with other flowers.

Hale and Hardy, and Easy to Start from Seed

Highly resistant to most pests and diseases, Rudbeckia is susceptible to leaf spot fungus. Infected plants will have small brown spots on their leaves that grow in size. Remove the infected foliage if it’s showing signs of this disease.Most deer and rabbits will ignore the plant entirely, but anything is on the menu when they’re hungry enough. I’ve seen slugs bother the base of the flowers and have even witnessed powdery mildew a few times, but that’s only in very wet conditions where black-eyed susan doesn’t enjoy being in the first place.

Garden Safe Neem Oil Extract Concentrate, 16 fl oz (2 Pack), available on Amazon

Black-eyed susans benefit from a handful of basic remedies to their minor ailments. Neem oil is helpful in stopping problem insects from eating treated plants. An aid in treating fungal problems that Rudbeckia can become afflicted by is this ready-to-use spray from Safer Brand. It can be used on other plants as well.

Be aware that this plant can be a tad assertive, self-seeding at will and crowding out other plants. When you’re first establishing plants from seed, roughly rake the soil and liberally sprinkle the area with your soon-to-be-flowers.

Rudbeckia seeds are sensitive to the worst of the cold weather. It’s suggested to wait until well after the cold weather is gone for the season before directly sowing seeds outdoors, ideally when the soil temperature has reached about 70°F.

Scratch the seeds into place and cover them loosely because they require light to germinate.

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I’ve started seeds indoors before, about 4 to 6 weeks before the last frost date, and in my experience this is the way to go. The flowers seem to handle transplanting well enough, and tend to bloom stronger and healthier than directly-sown seeds.

Just like with direct sowing, ensure the seeds aren’t covered too heavily with soil. Again, they need the light to germinate.

A few coworkers have told me that their own directly sown seeds take a year before they bloom, and they are trustworthy folks. I wouldn’t know because I can be a tad impatient and tend to sow my seeds a bit earlier than I’m supposed to… but I can certainly attest to Rubeckia’s aversion to frost and cold!

Green-Eyed Susan? Where to Buy Traditional and Unique Varieties

Several heirloom varieties do exist, and there are numerous hybrid cultivars available as well. Unless otherwise noted, all species of Rudbeckia will have the same blooming window, typically June through September or October.

An open-pollinated, heirloom variety is available from True Leaf Market. These seeds produce plants that are the iconic field and roadside black-eyed susan that we know and love.

Black-Eyed Susan Seeds

The seed quantities in these packages are massive, and better suited to direct sowing. Your run-of-the-mill seed packets purchased at garden centers and home improvement stores are ideal for starting a smaller batch of flowers. Expect them to reach somewhere between one and three feet in height.

Outside Pride sells its ‘Autumn Forest’ cultivar via Amazon. This plant features flowers with red and yellow petals. It’s a departure from the classic appearance of R. hirta but is appealing in its own right.

Outsidepride R. Hirta ‘Autumn Forest’ Seeds

You can order packets of 5,000 or 10,000 seeds, another quantity best suited for larger plantings or ideal to share among your neighbors and friends. They’ll reach a height of about two feet.

Outside Pride has also developed a unique ‘Green Eyes’ cultivar, available through Amazon. It’s got a snazzy little green center and reaches a height of about two feet. It certainly stands apart from its cousins and goes well with globe thistle.

Outsidepride R. Hirta ‘Green Eyes’ Seeds

This plant’s flowers show off olive green centers, rather than the traditional dark brown to black.

If you’re more of a classicist like myself, check out R. fulgida ‘Goldsturm’. It’s a more dense plant that’s more prone to mounding and growing to a restrained height, with smaller flowers that are still very much like the parent R. hirta.

R. fulgida ‘Goldsturm’

This variety also tolerates wetter soil than its counterparts and blooms June through September. Plants are available from Nature Hills.

You can also buy potted plants at greenhouses and garden centers in the growing season. I’ve seen black-eyed susans sold in two-gallon pots more often than any other size.

Shop the clearance racks at the high point of summer (after July 4th) and when mums and fall flowers start to arrive (usually September) to find discounted flowers like Rudbeckia in need of a home!

Joyful Allure

With its cheerful, daisy-like face and eager spreading habit, the black-eyed susan is a lover, not a fighter. And it just might make a happy addition to your garden.

As for me, you can bet your bottom dollar you’re going to see this flower in any garden I grow. It’s one of the few flowers that can follow you almost anywhere you go across the United States.

If you move around a fair bit like I do, having a trustworthy flowering friend that can follow you almost anywhere is the next best thing to keeping a permanent garden.

Have you ever grown R. hirta? Tell us what worked for this plant in the comments section below.

We’ve also got some great pairings to go with your poor land daisy. Try the stunning African daisy, a great annual with a variety of colors to choose from, and don’t forget about the awesome landscape grasses that are a match made in heaven for black-eyed susans.

Next up: check out our guide to perennial cutbacks for more information on properly caring for plants that return year after year.

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Photos by Matt Suwak, © Ask the Experts, LLC. ALL RIGHTS RESERVED. See our TOS for more details. Product photos via Garden Safe, Safer Brand, Outsidepride, Nature Hills Nursery, and True Leaf Market. Uncredited photos: . Revised and expanded from an article originally written by Gretchen Heber.

The staff at Gardener’s Path are not medical professionals and this article should not be construed as medical advice intended to assess, diagnose, prescribe, or promise cure. Gardener’s Path and Ask the Experts, LLC assume no liability for the use or misuse of the material presented above. Always consult with a medical professional before changing your diet or using plant-based remedies or supplements for health and wellness.

About Matt Suwak

Matt Suwak was reared by the bear and the bobcat and the coyote of rural Pennsylvania. This upbringing keeps him permanently affixed to the outdoors where most of his personal time is invested in gardening, bird watching, and hiking. He presently resides in Philadelphia and works under the sun as a landscaper and gardener, and by moonlight as a writer. An incessant questioning of “Why?” affords him countless opportunities to ponder the (in)significance of the great and the small. He considers folksy adages priceless treasures and is fueled almost entirely by beer and hot sauce.

How do you make so much bright yellow work in a border? Undercut it with the tawny colors of perennial grasses, which can create a neutral backdrop to frame the flowers.

Above: Photograph by Amanda Slater via Flickr.

Another tack to take is to give in to all that yellow optimism and plant a meadow or a prairie garden to make your black-eyed Susans look at home. The benefits are many: Black-eyed Susans have long-lasting blooms, will add color to a late summer landscape after many other flowers have faded, and are hardy, adaptable plants. After all, to flourish on a prairie, you need to be able to withstand wind, beating sun, dry spells, hail, drenching rainstorms, and even the occasional tornado.

Above: Black-eyed Susans blooming on Narragansett Bay. Photograph by Dr. Mary Gillham Archive via Flickr.

There are black-eyed Susans and there are brown-eyed Susans (equally lovely) and one of our favorite brown-eyed varieties is Rudbeckia triloba (a short-lived perennial in USDA growing zones 4 to 7 and an annual elsewhere).

Cheat Sheet

  • Black-eyed Susans will add a strong dose of golden color to a garden; a good foil for their cheery flowers is a backdrop of tawny perennials grasses.
  • Purple flowers also complement black-eyed Susans well; interplant them with Russian sage (Perovskia atriplicifolia) or purple asters.
  • For a perennial black-eyed Susan that will return next year in the same spot where you planted it, consider R. fulgida ‘Goldstrum’ if you live in USDA growing zones 4 to 9. (In zones 4 to 7, a short-lived perennial brown-eyed Susan is Rudbeckia triloba.)

Above: Yellow and purple: a happy combination. Here black-eyed Susans mingle with Verbena bonariensis against a backdrop of Stipa. Photograph by Amanda Slater via Flickr.

Keep It Alive

  • If you don’t cut down the seed heads, annual black-eyed Susans will reseed themselves and pop up in delightfully unexpected spots next year.
  • Depending on the variety, perennial black-eyed Susans will thrive in USDA growing zones 3 to 9 (with most cultivars happiest in zones 4 to 7).
  • In full sun or partial shade, with a moderate amount of rainfall or irrigation, black-eyed Susans will bloom from midsummer into September.

Above: Photograph by Miss Skittlekitty via Flickr.

For more growing tips, see Black-Eyed Susans: A Field Guide to Planting, Care & Design in our curated guides to Annuals and Perennials.

Does Black-eyed Susan Boost Immune System Like Echinacea Does?
Answered by: Conrad Richter
Question from: Meegwitch
Posted on: August 17, 2004
Can I use black-eyed susan as a substitute for echinacea for boosting the immune system?
Black-eyed susan is known scientifically as Rudbeckia hirta. There is evidence that at least several species of Rudbeckia have immunostimulatory activity similar to echinacea. This is not surprising because the genus Rudbeckia is very close to the genus Echinacea taxonomically.
We know that the First Nations people of North America used black-eyed susan to treat colds. Of course, the prevention and treatment of colds and flus is what echinacea is most famously used for.
Rudbeckia possesses complex polysaccharides with significant immunological activity. Polysaccharides play a similar role in echinacea, so there appears to be a chemical connection between the two genera, in addition to the close taxonomic relationship.
In one study (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=8688891), the immunostimulatory activity of Rudbeckia speciosa roots was compared to the activity of the roots of two species of Echinacea, E. angustifolia and E. gloriosa. It was found that Rudbeckia extract had a stronger effect than did the extracts from the two Echinacea species.
In another study, Rudbeckia subtomentosa was shown to contain two compounds called eudesmanolides that have significant antibacterial effects against Mycobacterium tuberculosis, the germ that causes tuberculosis.
Putting these pieces of information together it does seem likely that black-eyed susan has medicinal activity like echinacea, and it may even be more effective against colds and flus than echinacea. Certainly, more research is warranted.
Have sweet peas (flowers) any medicinal, culinary or cosmetic application?
According to the Plants For a Future database (http://www.ibiblio.org/pfaf/cgi-bin/arr_html?Lathyrus+odoratus&CAN=LATIND) sweet pea (Lathyrus odoratus) seeds are rich in vitamin A, though they are not necessarily edible as a food. Sweet pea has no known medicinal uses, but the essential oil from it sweet scented flowers is used in perfumery.

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