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Jack-in-the-Pulpit, a Flower Insects Would Die For!

by Bruce Crawford, Manager of Horticulture, Morris County Park Commission
Zoom in Arisaema triphyllum leaf.
Picture 1: Arisaema triphyllum leaf in early September in NH.

Most herbaceous plants are noted for their showy and colorful floral displays. In some cases, they may have the added benefit of attractive foliage that will help carry interest within the garden well beyond the flower display. However, it is far more rare for a plant to be known for flower, foliage and 'fruit'! Such are the benefits of Jack-in-the-Pulpit, botanically known as Arisaema triphyllum. Often overlooked by many, it is a fascinating native species of our woodlands with an innocence that belies its 'killer' alter ego!

Arisaema is a member of the Araceae or Arum Family with over 180 species found predominantly in the Himalayas, China, Japan and Southern Asia, although several species are found in eastern North America and tropical northeastern Africa. Arisaema triphyllum is the predominant native species of eastern North America, growing from Nova Scotia south to Florida, west to Minnesota and Louisiana. The genus name was crafted in 1831 by the German botanist Carl Friedrich Philipp von Martius (1794–1868). The name is derived from the Greek Aris meaning Arum and Haema, meaning red in recognition of the red coloration appearing on the leaves and stems of certain species, as seen on the leaf petiole and protective leafy sheaths in Picture 2.

Zoom in Arisaema triphyllum in May.
Picture 2: Red leaf petiole and protective sheath in May in NJ.

Jack-in-the-Pulpit was originally named Arum triphyllum in 1753 by the Swedish botanist Carl Linnaeus (1707–1778), with the species epithet honoring the 3 prominent leaflets that constitute a leaf (Picture 1). Interestingly, it was only one year after Martius had proposed the new genus of Arisaema that the German botanist Heinrich Wilhelm Schott (1794–1865) reclassified this species as Arisaema triphyllum! Schott specialized in the study of Aroids and he quickly recognized this plant readily met the description of an Arisaema and not an Arum!

Of course, that begs the question – what is the difference between the two genera? Unique to the genus Arisaema, plants undergo a rather unique and rare phenomenon called sequential hermaphrodites, whereby the sex of the flower changes from male to female as the plant develops from seedling to maturity. The process is triggered through an increase in stored nutrient reserves within the corm. A corm resembles a bulb in appearance but, is a modified stem rather than layers of modified leaves characteristic of bulbs. Some Arisaema species grow from somewhat different modified stems called tubers. During the initial years following germination, the 3–5" tall plants appear as a whirl of 3 leaflets without any flowers. Many gardeners actually mistake it for poison ivy, prematurely removing it before it has a chance to grow and flower! After five years, the corm has typically grown to a size whereby the nutrient reserves are able to support the development of male flowers, with female flowers finally appearing several years later. The additional time and nutrient reserves are needed to ensure fruit development following pollination of the female flowers. Interestingly, if the plant endures undue stress, such as annual browsing by herbivores or several years of drought, the plant often reverts to presenting only male flowers.

Zoom in A plant in mid-summer.
Picture 3: A plant in mid-summer.

The foliage of mature plants typically grows from 1–2' tall (as seen in Picture 3) with the flower structure appearing on a short stem emerging just below the leaf petioles and roughly ½ the height of the foliage. The overall flower structure is typical to members of the Araceae, whereby a specialized, cup-shaped leaf called a spathe appears in April. With a touch of imagination, the spathe appears much like a pulpit. There is even a hood extending over the top of the pulpit that appears like a sounding board used to project voices outwards to the congregation (Picture 4). The true function of the hood is to prevent unwanted light and rainwater from entering the pulpit; too much rainwater would cover the flowers near the base of the pulpit and interfere with pollination. Within the pulpit stands 'Jack', botanically called a spadix. The spadix is a slender upright organ with either male or female flowers arranged radially around the basal inch or so of the structure. The flowers are well-hidden and protected by the spathe. The upper, club-like portion of the spadix appears above the rim of the pulpit and releases scents to attract pollinators, a typical trait for members of the Araceae.

Zoom in Arisaema triphyllum spathe.
Picture 4: Close-up of the spathe in early May in NJ.

Unique to Jack-in-the-Pulpits is the strategy by which the flowers are pollinated. Although the overall flower appears to be 'innocent' to the casual eye, it is oddly uncaring about its pollinators. For Arisaema triphyllum, the chief pollinator are two species of fungus gnats. The spadix emits a fragrance similar to mushrooms and shelf fungus, where the gnats lay their eggs and the resulting larva feed. This fragrance obviously serves to draw the gnats into the open mouth of the spathe. However, once inside the design of the spathe serves to confuse the gnat making it is near impossible for it to escape via the opening through which it came! Elements of the 'floral architecture' that contribute to this confusion include the base of the 'Pulpit' being thinner and more translucent to light (notice the white color at the base of the pulpit in Picture 4). This lures the gnats to the bottom of the pulpit on the impression this brighter region is in fact an opening to the outside. The overhanging hood that covers the pulpit also serves to reduce the amount of sunlight entering the pulpit, darkening the upper portion of the spathe and further disorienting the insects. As seen in Picture 4, the inside of the hood is often a dark purplish brown, serving to once again make the entrance appear even darker and enhancing the brighter region at the base. In an effort to prevent the gnats from walking up the side of the spathe to freedom, the inner layer of the spathe is lined with a slippery waxy coating and most spathes have light green vertical stripes, guiding the gnat downwards as well. It's the perfectly designed trap!

Drawn to the base, the gnat flies about and if within a spathe featuring male flowers, it becomes coated with pollen. Interestingly, the spathe with male flowers also features an exit hole near the base, allowing the now pollen laden insect to escape. Unfortunately for the none-too-bright gnat, the spathe surrounding female flowers does not have an exit hole. As the trapped insect flies about in search of an exit, it pollinates the female flowers and ultimately perishes.

It is highly unusual for a plant to kill its pollinator. In fact, Arisaema is potentially the only genus known with this adaptation, again separating it from the genus Arum. The pressure for this adaptation is only speculative, but the most obvious theory is to insure pollination and there is no need for the plant to expend energy on an exit. Another explanation is the reduction of competition, an explanation that could initially be perceived as selfish, yet in reality is more focused on statistics. By eliminating the pollinator, female flowers of other plants are less likely to be pollinated, thereby reducing the potential for what will eventually become additional male flowered seedlings. If the gnats are 'wasting' time and energy repeatedly visiting male flowered plants, there is less opportunity for pollinating female flowers. Of course, it is a numbers game – if the male plants are too few in number and gnats visit the 'lethal' female flower first, that too will impact reproduction! Killing and reducing the number of pollinators may be a method to keep the male/female balance in check!

Zoom in Red fruits.
Picture 5: Red fruits in early September in NJ.

Throughout the course of the summer, the glossy foliage of Jack-in-the-Pulpits remains attractive with the petioles and stems of some plants beautifully marked with varying length dashes of purple and green as seen in Picture 6. The developing green fruits remain partially hidden during early summer by the dried remains of the spathe, which slowly falls away as the seeds expand and mature to a bright red. Come late August and September, the foliage too withers, fully exposing the red fruits held upright on the stem (Picture 5). They resemble a small ear of corn with red kernels although it is certainly not edible! All portions of Jack-in-the Pulpit are dangerous to eat due to the presence of calcium oxalate crystals that create a sensation similar to shards of glass piercing the tongue and mouth. It is usually sufficient to keep deer browse to a minimum! The fleshy fruits serve as food source for Wood Thrushes, Wild Turkeys and various rodents. They are also double dormant, requiring a winter followed by a summers' warmth and yet again another winters' chill before germinating.

Species native to Asia are also known as Cobra Lilies, since the Spathe of many species resembles the head of a snake! Of the species available, Arisaema sikokianum is a strikingly beautiful plant that I have long admired. Hardy to zone 5, the plant was described and published in 1879 by the French botanists Adrien René Franchet (1834–1900) and Paul Amedée Ludovic Savatier (1830–1891). Savatier served in the French military as a physician and botanist and from 1865–1875 he was stationed in Japan as part of Frances' efforts to develop a Japanese navy. He worked alongside a number of Japanese botanists and together with Franchet, they published a two-volume treatise on Japanese plants, with Vol. 1 published in 1875 and Vol. 2 in 1879. The species is native to the island of Shikoku, inspiring the species epithet.

Zoom in Arisaema triphyllum coloration.
Picture 6: Coloration of the stem in July.

When Arisaema sikokianum first emerges, the encircling leaf sheathes are an attractive brown with light brown markings. I find it pairs beautifully with the winter bronzed foliage of Alleghany Pachysandra (Pachysandra procumbens) as seen in Picture 7. What makes this 'Jack' uniquely beautiful is the chalk white spadix and interior of the spathe, which contrasts nicely with the dark purple, nearly black exterior, as seen in Picture 8 and 9. Furthermore, the exterior of the spathe and the hood is accented with vertical green stripes. Of course, plants 'select' colors to either attract pollinators or seed dispersing agents and in this case, it is to once again attract fungus gnats as pollinators! The brilliant white color resembles the color of shelf fungus and mushrooms. In fact, the upper end of the spadix is enlarged and actually resembles a mushroom! It also emits a fungus-like odor, enhancing the lure for the unsuspecting gnats.

As before, the spathe is designed to confuse the gnats upon entry; the base of the spathe is translucent to light and it actually appears to glow in relation to the rest of the opaque structure when illuminated by the sun. The vertical green lines of the hood also serve to guide the pollinators to the base of the pulpit. Similar to its North American cousin, the spathe encompassing male flowers provides an exit hole near the base while those surrounding female flowers lack this exit strategy.

Arisaema sikokianum also provides beautiful foliage. More compact than Arisaema triphyllum, it grows from 1–1.5' tall with the leaf divided into three to five leaflets. The center of each leaflet is marked by attractive white variegation that persists throughout the summer (as seen in Picture 10). By September, the fruits once again turn red and provide colorful autumn interest.

Zoom in Arisaema sikokianum spathe and spadix.
Picture 7: Arisaema sikokianum emerging sheath on April 15.
Zoom in Arisaema sikokianum.
Picture 8: Arisaema sikokianum spathe and spadix on April 23.
Zoom in Arisaema sikokianum emerging sheath.
Picture 9: Spathe and spadix in early May.

All Arisaema enjoy dappled shade in organic rich soils that are not prone to drought. Plants are long-lived, typically lasting for well over 20 years and produce ample offspring during their lifetime. If the soils remain sufficiently moist, I have seen plants seed and thrive on sites receiving strong sunlight throughout most of the day. They are pH adaptable, growing equally well in acidic as in alkaline soils.

Since my youth I have studied and enjoyed our North American Jack-in-the-Pulpit while hiking or as it volunteered in woodlands around my home. Arisaema sikokianum was the first Asian species that I grew beginning in the early 1990's. Throughout the years, I have always enjoyed the beauty of these two species, but never would have guessed its unique and complex processes of reproduction. Whether it is the attractive foliage, colorful flower structures or bright red fruits come fall, this is indeed a 'killer' of a plant for your garden!

Arisaema sikokianum leaf variegation.
Picture 10: Leaf variegation of Arisaema sikokianum in late May.