St. John’s Wort – Learn How to Choose

When looking for a low-growing native plant for the forefront of our perennial sun garden, I became interested in St. John’s wort. Many of the sun-loving natives in our garden are tall and tend to become leggy as the growing season progresses. St. John’s wort seemed to be a possible native filler plant that could hide the leafless bottom portion of tall plant stems.

When I asked gardeners about the pros and cons of St. John’s wort, they gave mixed reviews. Some said that the nonnative species are invasive; some said even the native species are invasive. There even seemed to be confusion about which species are native. After beginning my research, I realized that one reason for the confusion is that there are almost 500 different species of Hypericum, many of which are commonly referred to as St. John’s wort. Plants of the genus Hypericum were apparently gathered and burned to ward off evil spirits on the eve of St. John’s Day, thus giving rise to the genus common name of St. John’s wort. To avoid the confusion of overlapping common names for different species, it is advisable to use the Latin name when identifying Hypericum for purchase.

Daunted by the prospect of almost 500 different species including perennials, trees, and shrubs, I decided to consult two main sources to identify the Hypericum species native to our area: the Piedmont Virginia Native Plant Database and the Native Plant Finder By Zip Code.

The Piedmont Virginia Native Plant Database lists one hypericum native to our area: bushy St. John’s wort or dense St. John’s wort (Hypericum densiflorum).

The Native Plant Finder By Zip Code cites 5 species of Hypericum that are native to zip code 22901:

• shrubby St. John’s wort (Hypericum prolificum)
• spotted St. John’s wort (Hypericum punctatum)
• St. Andrew’s cross (Hypericum hypericoides)
• St. Peter’s wort (Hypericum crux-andreae)
• orangegrass or pineweed (Hypericum gentianoides)

In addition to these six native species, I will also cover two additional nonnative species that are commonly found in nurseries in our area: Hypericum perforatum and Hypericum calycinum.

NONNATIVE HYPERICUM SPECIES

Hypericum perforatum

Common St. John’s wort or perforate St. John’s wort (Hypericum perforatum) is native to Europe, North Africa, and Southwest Asia. It is also commonly called goatweed or Klamath weed.

Plants were first brought to North America by settlers in 1696 and have naturalized over time throughout much of the continent. H. perforatum is classified as a noxious weed in over 20 countries. In the U.S., it is classified as an invasive or noxious weed in several states including Oregon, California, Washington, Montana, Nevada, Utah, Wyoming, West Virginia, and Indiana. It is also listed on Alaska’s list of exotic plants.

The species grows 1-3’ tall. It has small, paired, ovate leaves. Most leaves have scattered, tiny translucent dots; when held up to the light, they give the impression that the leaf is perforated (where the scientific name comes from). Yellow, star-shaped, ¾” flowers are 5-petaled with many stamens and have tiny black dots around the edges. (See dots in the photo above.) Flowers bloom in June-August. The foliage has an unpleasant aroma when bruised or rubbed. Although tolerant of most soil types, the plant prefers moist, well-drained soil. The species can grow in either full sun or in partial shade, but it flowers more profusely in full sun. It spreads by rhizomes and, once established, it can be highly invasive and very difficult to remove. Its seed can be dispersed by wind, water, humans, and other animals. Seed can lie dormant in the soil seed bank for many years and germinate once the soil is disturbed. As an invasive, common St. John’s wort can replace native plants in natural ecosystems.

The compound, hypericin, is found in stems, leaves, flowers, and seeds, and causes blistering and itching on light-haired or unpigmented skin exposed to intense sunlight. When an animal eats H. perforatum, hypericin reaches the skin from an internal route (stomach to blood to skin). It then sensitizes white or unpigmented skin to sunlight and causes lesions. In large doses, it is poisonous to livestock, especially horses and cattle.

Hypericums have historically been used as herbal medicines, but H. perforatum is the one most commonly used today. Although toxic, H. perforatum has been used to treat people for depression, nervousness, and insomnia. It has been used externally to treat minor wounds, inflammations, burns, skin disorders, and nerve pain. It is banned in France and is available only by prescription in many other countries. According to the NIH National Center for Complementary and Integrative Health: “It has been clearly shown that St. John’s wort can interact in dangerous, sometimes life-threatening ways with a variety of medicines. (See this NIH link for more information on toxicity and safety warnings.) It is sold in the U.S. as a dietary supplement; such supplements have lower standards for approval than over-the-counter medicines.

Hypericum calycinum

Commonly called Aaron’s Beard or creeping St. John’s wort, Hypericum calycinum is native to Southern Europe and southwestern Asia. This stoloniferous subshrub or shrublet typically grows to 12″ (less frequently to 18″) high and 24″ wide and is frequently planted as a ground cover. Large, 5-petaled yellow flowers are about 3” with numerous, erect stamens that give a powder-puff appearance in summer. Although H. calycinum tolerates a wide range of soils, it thrives in sandy soils in full sun; it is less floriferous in part shade. In full sun, the 4” long leaves are a rich green; in shade, they are a lighter, yellowish green; in fall, the leaves turn purplish. This species spreads rapidly by underground stems and can spread aggressively in ideal growing conditions, such as in Oregon, where it is listed as an invasive. It is not listed as an invasive plant by the United States Department of Agriculture, and it is not toxic. Once established, it can be difficult to remove. In addition to spreading by rhizomes, its tap root and vertical roots can extend 5’ deep. Wilt and root rot can be significant problems, particularly in hot and humid climates of the South.

When massed on slopes, hillsides, or embankments, H. calycinum is effective for stabilizing soil. It is also used in rock gardens, border fronts, naturalized plantings, and as an edger for open woodland gardens. If considering this plant, be aware of its potential spreading characteristics. You might consider using native hypericum species as an alternative. (See the Missouri Botanical Gardens blog comments from home gardeners for observations on the spreading characteristics of H. calycinum. Of course, the reliability of these comments depends on whether the home gardeners are correctly identifying the species.)

HYPERICUM SPECIES NATIVE TO OUR AREA

Hypericum densiflorum

Bushy St. John’s wort (Hypericum densiflorum) is a native shrub that can grow up to 6’ tall with a spread of 3-6’ wide. It is native to eastern U.S. and west to Texas and occurs on acidic soils in moist and wet conditions, including streams, ponds, lake banks, seepage slopes, and wet meadows. It is adaptable to a variety of moisture levels and, once established, has some drought resistance. It tolerates a variety of soil types, including clay, loam, sand, and shallow rocky soil. Beautiful, finely-textured foliage turns yellow/gold in fall. Clusters of 5-petaled, yellow flowers with multiple stamens appear in dense, flat-topped cymes from June-September. Flowers give way to interesting cone-shaped pods which split in the fall and persist all winter. The glossy, coppery-colored bark of mature shrubs adds visual interest to the winter landscape. This shrub is easily grown in average, well-drained, moist garden soil in full sun to partial shade. Plant in groups, shrub borders, foundations, or as a hedge. It works well in a native/pollinator garden, a rock garden, or on slopes for erosion control. It is generally free of pests and diseases.

According to the Invasive Plant Atlas of the United States, this species does not appear on any state or national invasive species lists. According to the Chesapeake Bay Foundation, it can spread aggressively, so be sure to allow room if you choose this species.

Hypericum prolificum

Shrubby St. John’s wort (Hypericum prolificum) is a small, mound-shaped, deciduous shrub growing 2-4’ tall, with dense, upright branching. The lower stems are woody with shredded gray-brown bark, while the upper stems are green. The root system is woody and branching. Dark green, lance-shaped leaves are 2-3″ long and turn yellow-green in fall. Bright yellow, 5-petaled flowers (to 1″ diameter) have numerous, yellow stamens. Stamens are bushy to the point of partially obscuring the petals (hence the species name of prolificum which refers to the stamens). Flowers appear from June-August. Each flower is replaced by a cone-shaped seed capsule about 1/3–1/2″ in length, which splits in autumn to release black seeds. The flowers are cross-pollinated primarily by bumblebees, which collect pollen for their larvae. Sometimes butterflies and wasps land on the flowers in search of nectar, but the flowers offer only pollen. Caterpillars of the butterfly Strymon melinus (gray hairstreak) feed on the seed capsules, and caterpillars of Nedra ramosula (gray half-spot), and other moths, feed on the leaves. This native plant occurs on rocky ground, dry wooded slopes, uncultivated fields, gravel bars along streams, and in low, moist valleys. It tolerates a wide range of soils, including dry rocky or sandy soils, and it can grow in full sun to part shade. It also tolerates some drought. Although it has no serious disease or insect problems, root rot and wilt can be significant problems in hot and humid climates. Mass or group this species in the shrub border, include it in a native plant garden, or grow it as a hedge. It is also useful for stabilizing embankments. According to the list compiled by Rutgers on “Landscape Plants Rated on Deer Resistance,” H. prolificum earns a B, which is “seldom severely damaged.”

According to the Invasive Plant Atlas of the United States, this species does not appear on any state or national invasive species lists.

Hypericum punctatum

Spotted St. John’s wort (Hypericum punctatum) is a perennial herb that grows up to 2 ½’ tall, branching occasionally in the upper half. Hairless, erect stems are multiple from the base and mostly unbranched, except in the flower cluster. Hairless, opposite leaves are up to 2½” long and 1″ across. They are oblong, oval, or bluntly lanceolate (with rounded tips). New leaves are heavily dotted with black glands around the edges and on the underside. (The invasive species, H. perforatum, has translucent dots on the leaves.) Tight clusters of yellow flowers bloom during midsummer, and the bloom period lasts for about a month. Each flower is a little less than ½” across and has 5 petals. In the center, a flask-shaped pistil is surrounded by numerous yellow anthers on long styles. The easiest way to distinguish spotted St. John’s wort from other similar species involves an examination of the flower petals. For spotted St. John’s wort, dark dots and streaks can appear anywhere on the upper surface of the yellow petals, whereas for other species of St. John’s wort, such dots and streaks are confined near the margins of the petals, or they are completely absent. There is no floral scent. The plant can grow in full or partial sun; moist to mesic (moderate or well-balanced supply of moisture) conditions; and a rather lean soil, which reduces competition from taller plants. Rocky or gravelly soil is quite acceptable. Occasionally, the leaves turn brown in response to drought; otherwise, this plant has few problems.

H. punctatum is pollinated by insects and has special value to bumblebees and sweat bees. It also attracts beetles and hoverflies although these insects pollinate to a lesser extent. Its flowers do not produce nectar; insects are attracted by the pollen. Gray hairstreak caterpillars feed on the seed capsules and gray half-spot caterpillars feed on the leaves. Though insects eat the plant, foraging mammals seldom feed on the foliage which contains hypericin.

Numerous tiny seeds are scattered by the wind when the stems sway back and forth. The root system consists of a branching taproot and short rhizomes. Although vegetative colonies of this plant can develop from the rhizomes, I did not find any warnings on invasiveness.

According to the Invasive Plant Atlas of the United States, this species does not appear on any state or national invasive species lists.

Hypericum crux-andreae

St. Peter’s wort (Hypericum crux-andreae) is a small, upright shrub that grows 1-3’ tall with 4-petaled flowers, instead of the usual 5 petals generally characteristic of other St. John’s worts. (This Latin name is correct, even though it seems to go with St. Andrew’s cross.) The sepals are of very unequal sizes. Brilliant lemon-yellow flowers form at its branch tips, and bloom from June-October. The slender shrub has opposite, pale green, oval-to-oblong leaves about 3/4’’ wide, and shedding bark on older wood. In its native habitat, this shrub is usually found in moist sandy woods, pinelands, stream banks, wet prairies, and pond margins. It can also appear in disturbed fallow fields. Seed dispersal is thought to be by gravity. It prefers partial sun and is adaptable to different soils. It ranges from New York south to Florida and west to Texas; in the north, it may form a mat on the ground. St. Peter’s wort is critically imperiled in Florida, according to the Institute for Regional Conservation. According to the U.S. Department of Agriculture, it has disappeared from Pennsylvania, and Kentucky lists it as threatened.  H. crux-andreae has been observed to host skippers such as Panoquina ocola (family Hesperiidae).

I didn’t find any mention of invasiveness, nor was this species included on invasive lists.

Hypericum hypericoides

St. Andrew’s cross (Hypericum hypericoides) is a small shrub growing 1-3’ tall. The common name refers to St. Andrew, the patron saint of Scotland, who is said to have been martyred by crucifixion on an x-shaped cross. The flowers are small (<1”) and creamy yellow with four narrow petals arranged in an “X.” (The 4 petals are narrower than those of St. Peter’s wort.) The flowers have many prominent yellow stamens and 4 unequal sepals. It blooms from July-October, although in some zones its bloom period is given as May-August. Leaves are opposite and may be linear, elliptical, or ovate, and up to 1/3” wide, which is narrower than the leaves of St. Peter’s wort. Stems are branched and reddish-brown. Fruits are reddish-brown ovoid capsules. Propagation is by seed and dispersal is generally thought to be by gravity; some seeds were discovered in a 112-year-old field site. Preferred sites are wet to moderately dry, well-drained, or calcareous soils in partial sun. It ranges from New York to Florida and west to Texas. It is sometimes found in the same habitat as St. Peter’s wort. This species is known to be eaten by white-tailed deer, mostly during the winter. On the state level, H. hypericoides is considered vulnerable in the state of Delaware.

According to the Invasive Plant Atlas of the United States, this species does not appear on any state or national invasive species lists.

Low St. Andrew’s Cross (H. suffruticosum) is only 2 ½ – 6” tall, with usually only 2 sepals, the flowers eventually nodding; it is found in sandy sites in the coastal plain from South Carolina south to Florida and west to Louisiana.

 

Hypericum gentianoides

Orangegrass or pineweed (Hypericum gentianoides) is the only annual St. John’s wort from our list. With tiny yellow flowers that open only in the sun, and scaly leaves on erect, wiry branches, its appearance is also unlike other St. John’s worts. Generally, H. gentianoides flowers from July-October; however, it has been observed flowering in May through July and September. Its seed capsules are usually red. It proliferates in fields, rock outcrops, woodland borders, eroding areas, pond margins, and flatwoods. Although it most often occurs in non-wetland habitats, it can also occasionally be found in wetland habitats.  It mostly grows in open areas with sandy or rocky soils; it can also tolerate partial shade. It is distributed from Maine and Ontario west to Minnesota, and south to southern Florida and Texas. It propagates by seed which is believed to be dispersed by gravity. When crushed, its leaves give off a citrus smell.

H. gentianoides is listed as endangered by the Iowa Department of Natural Resources Parks, Recreation, and Preserves Division. It is also considered vulnerable in Michigan, imperiled in Vermont, critically imperiled in Oklahoma and Ontario, and is an exotic species (not native) in the Canadian provinces of New Brunswick, Nova Scotia, and Prince Edward Island.

It is not included on invasive lists for the U.S. However, its listing as an exotic species in the three Canadian provinces mentioned above plus Ontario, indicates that it may have worrisome invasive characteristics.

HYPERICUM IN THE FOOD WEB

According to the Native Plant Finder by Zip Code, Hypericum species that are native to zip code 22901 are the larval host plants for 23 species of butterflies and moths. Hypericum species are attractive to many native bees including: polyester, yellow-face, large carpenter, bumble, leafcutter, resin, and sweat bees, as well as to gray hairstreak butterflies, whose caterpillars feed on the seed capsules, and to gray half-spot moths, whose caterpillars feed on the leaves. Hoverflies and skippers are also attracted to some species. Shrubby St. Johns wort produces seeds that persist all winter, making it a favorite of finches and sparrows.

SUMMARY

The Hypericum genus is a fascinating collection of plants comprising almost 500 species. The research for this article was done with the perspective of identifying native species that might be used in home landscapes. I was particularly interested in identifying species that would be good “filler” plants in the lower layer of perennial gardens. After my research, the two non-native Hypericums are not attractive as possible additions to the landscape: H. perforatum is very invasive, and H. calycinum may be invasive, especially in conditions that are attractive to the plant. Unfortunately, these are the Hypericum species that seem easiest to purchase.

Of the native species, there are a few candidates for home landscaping that could be very attractive, depending on your landscape’s moisture and sunlight conditions, and available space. Most species are described as being adaptable. H. densiflorum is attractive as a larger-sized shrub, if there is enough space for it to spread. It has attractive foliage, good fall color, a long bloom period, and attractive seed pods and interesting bark for winter interest. It does well in moist and wet conditions. H. prolificum is a small shrub that does not appear to have spreading characteristics. It has a long bloom period, and performs well in a range of soil, moisture, and light conditions. (This species sounds promising although it can grow to 4’ tall.)  H. punctatum seems like a possible candidate for the filler layer. It’s a perennial herb that grows to 2 ½’ and has a long bloom period. It’s adaptable to a range of conditions except for drought. It is attractive to bees. It does contain hypericin which may be a problem for dogs or cats who eat plants. The hypericin content means it will be deer resistant. H. crux-andreae is a small shrub that likes moist conditions in partial sun. H. hypericoides is a small shrub that likes semi-shady, wet- to moderately-dry areas. Neither of these shrubs are invasive. Unfortunately, H. hypericoides is susceptible to deer browse. The annual species, H. gentianoides, is mainly found in dry areas with sun. It is listed as an exotic species (nonnative) in several eastern Canadian provinces which means it must have some invasive characteristics in those areas. The availability of these lesser-known species might be a challenge. Working with local native plant nurseries would be the most promising approach.

SOURCES

Piedmont Virginia Native Plant Database, http://webapps.albemarle.org/NativePlants/list.asp

Native Plant Finder by Zip Code, https://www.nwf.org/NativePlantFinder/Plants/1707

“Hypericum perforatum, Common St. John’s Wort,” Minnesota Wildflowers, https://www.minnesotawildflowers.info/flower/common-st.-johnswort

“Hypericum perforatum,” Royal Horticultural Society, https://www.rhs.org.uk/plants/9021/hypericum-perforatum/details

“St. Johnswort: Identification, Biology, and Integrated Management,” Montana State University Extension, https://apps.msuextension.org/montguide/guide.html?sku=MT199810AG

“St. John’s Wort, Hypericum perforatum,” National Center for Complementary and Integrative Health (NIH), https://www.nccih.nih.gov/health/st-johns-wort

Common St. John’s Wort, Hypericum perforatum L., Invasive.org., https://www.invasive.org/browse/subinfo.cfm?sub=4411&start=1

‘Hypericum calycinum, NC State Extension, https://plants.ces.ncsu.edu/plants/hypericum-calycinum/

“Aaron’s Beard, Hypericum calycinum L., Invasive Plant Atlas, https://www.invasiveplantatlas.org/subject.html?sub=18314

“Hypericum calycinum,” Missouri Botanical Garden, http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=a520

“Hypericum densiflorum, Bushy St. John’s Wort,” NC State Extension, https://plants.ces.ncsu.edu/plants/hypericum-densiflorum/

“Hypericum densiflorum, Bushy St. John’s Wort,” Mt. Cuba Center, https://mtcubacenter.org/plants/bushy-st-johns-wort/

“Hypericum densiflorum,” Chesapeake Bay Native Plant Center, http://www.nativeplantcenter.net/plants/hypericum-densiflorum/

“Spotted St. John’s Wort, Hypericum punctatum,” Illinois Wildflowers, https://www.illinoiswildflowers.info/prairie/plantx/sp_stjohnwortx.htm

Spotted St., John’s Wort, Hypericum punctatum, Minnesota Wildflowers, https://www.minnesotawildflowers.info/flower/spotted-st.-johns-wort

“Shrubby  St. John’s Wort – Hypericum prolificum,” Illinois Wildflowers, https://www.illinoiswildflowers.info/prairie/plantx/sh_stjohn.htm

“Flower Friday: St. Andrew’s Cross, Hypericum hypericoides,“ Florida Wildflower Foundation, https://flawildflowers.org/flower-friday-hypericum-hypericoides/

“Hypericum hypericoides,” Ladybird Johnson Wildflower Center, https://www.wildflower.org/plants/result.php?id_plant=HYHY

“Hypericum crux-andreae, St. Peter’s Wort,” Lady Bird Johnson Wildflower Center, https://www.wildflower.org/plants/result.php?id_plant=HYCR3

“St. Peter’s Wort, Atlantic St. Peter’s Wort,” Texas Native Plants Database, Aggie Horticulture, https://aggie-horticulture.tamu.edu/ornamentals/nativeshrubs/hypericumcrux.htm

“St. John’s Wort, or St. Peter’s Wort, or St. Andrew’s Cross?” NC Cooperative Extension, https://lee.ces.ncsu.edu/2018/11/st-johns-wort-or-st-peters-wort-or-st-andrews-cross/

“Hypericum gentianoides,” Lady Bird Johnson Wildflower Center, https://www.wildflower.org/plants/result.php?id_plant=HYGE

“Pineweed (orange grass), Hypericum gentianoides, Connecticut Botanical Society, https://www.ct-botanical-society.org/Plants/view/283

“Hypericum gentianoides,” University of Michigan LSA Herbarium, https://michiganflora.net/species.aspx?id=1461

Indiana Invasive Species Council, https://www.invasive.org/species/list.cfm?id=167

California Invasive Plant Council, https://www.invasive.org/species/list.cfm?id=64

Montana Noxious Weeds, https://www.invasive.org/species/list.cfm?id=38

Oregon Noxious Weeds, https://www.invasive.org/species/list.cfm?id=56

Nevada Noxious Weeds, https://www.invasive.org/species/list.cfm?id=29

Alaska Exotic Plant Information Clearing List, https://www.invasive.org/species/list.cfm?id=86

Utah Noxious Weeds, https://www.invasive.org/species/list.cfm?id=33

Washington Noxious Weeds, https://www.invasive.org/species/list.cfm?id=61

West Virginia Invasive Species Strategic Plan and Volunteer Guidelines 2014, https://www.invasive.org/species/list.cfm?id=184

Wyoming Noxious Weeds, https://www.invasive.org/species/list.cfm?id=40

“St. John’s Wort, Friend or Foe?” myMotherLode.com, https://www.mymotherlode.com/news/local/310245/st-johns-wort-friend-or-foe.html

“A Review of Some Biological Control Programs for Invasive Plants,” Ontario Invasive Plant Council (pp.21-28), https://www.ontarioinvasiveplants.ca/wp-content/uploads/2016/06/Bill-MacIlveen-1.pdf

Feature Photo: shrubby St. John’s wort (Hypericum prolificum) Photo: Susan Martin, Ivy Creek Natural Area, Charlottesville, VA