Skunk, Jacks & Dragons: The Curious Arum Family
Updated: Dec 13, 2017
Jack-in-the-Pulpit (Arisaema triphyllum) unfurling in April.
As July moved into August of 2016, gargantuan Titan Arums were blooming all around the U.S.—in botanical gardens and greenhouses, of course; this peculiar plant, also charmingly called Corpse Flower, is native to Sumatra. In my hometown of Bloomington, the Indiana University greenhouse live-streamed the blossoming of its own titan, “Wally” and visitors queued up to see this rare event, as well as to get a whiff of the flowers' rotten-meat aroma.
Although not as dramatic as their titanic tropical cousin, our Indiana Arums are fascinating their own right. They all share the curious inflorescence (flower head) characteristic of the Arum family, comprised of spadix (the fleshy central spike on which flowers grow) and spathe (the leaf-like structure that emerges from the shoot below the spadix, and partially encloses it like a hooded cowl).
One function of the spathe-and-spadix set-up is to generate heat. The Skunk Cabbage, emerging in wetlands as early as February, is capable of thermoregulation, typically the domain of mammals: through cellular respiration its egg-shaped spadix heats up, and the surrounding spathe acts as an insulator, raising the inner temperature of the inflorescence up to 70 degrees Fahrenheit and allowing the plant to melt its way through snow and ice.
Skunk Cabbage (Symplocarpus foetidus) is able to bloom as early as February due to its ability to generate its own heat.
This toasty temperature keeps the flowers from freezing, and also wafts the Skunk Cabbage’s fetid odor about, drawing pollinators—mostly flies--into the spathe. Honey bees also visit the flowers, procuring from them an important early source of pollen. The warmth inside the spathe attracts the bees and helps them maintain enough body heat and energy to fly from one plant to another, and finally back to their hive.
Skunk Cabbage is not readily available for growing in a garden setting, but two arums that are especially abundant in the forests of southern Indiana make wonderful, carefree garden plants. They merely require light shade and moist soil rich in organic matter to thrive. Jack-in-the-Pulpit is well known for its whimsical inflorescence, the usual Arum arrangement of spadix (Jack) and spathe (the pulpit). Green Dragon also has spathe and spadix, but unlike Jack--a blunt spike peeking from beneath the spathe’s hood--the Dragon’s spadix is long and tapered, extending far beyond the spathe.
Jack-in-the-Pulpit (Arisaema triphyllum).
Green Dragon (Arisaema dracontium).
At the base of the spadix column are clustered tiny flowers—sexual parts only, without extraneous petals, sepals or nectaries. The plants don’t contribute much in the way of bright blooms to the landscape: the Jack’s inflorescence ranges in color from cream to green to dark maroon, while the Dragon’s is greenish-white. In larger plants the spathes are often hidden beneath the leaves, but these unique compound leaves, which remain into late summer, add great interest and texture to the garden.
Green Dragon (Arisaema dracontium).
What insects are lured into subtle, hidden flowers, enticed by an aroma of mushrooms-- with perhaps a soupçon of warm decay? Don’t expect those glamour pollinators, the bees and butterflies, to show up; indeed, you may never even see the insects that make reproduction happen for these two Arums--they are the unassuming, unsung pollinators: tiny flies, thrips, springtails and fungus gnats.
These wee insects don’t even benefit from their efforts. They crawl down into the spathe expecting to find fungus or decaying matter upon which to dine or lay eggs, and fumble around the flowers clustered at the bottom, thereby picking up or depositing pollen. They may then escape the spathe of a male plant through a small aperture at the bottom, but from a female inflorescence, there is sadly no exit.
And so to another curious feature of Jacks and Dragons: they may be male, female, or both, and can control which gender they express. It takes about 5 years for a plant to produce flowers after it germinates, and while it is still small, it produces only male flowers. If conditions are favorable and it continues to increase in size every year, it will eventually transition to female flowers, which require a greater investment of energy. Both male and female flowers may be found together on Green Dragon, but Jacks usually transition completely between one and the other. Gender is reversible as well: in times of stress--drought, for instance-- a female plant can revert back to being male.
Jack-in-the-Pulpit fruits, autumn.
The female plants of Jack-in-the-Pulpit and Green Dragon can be quite impressively robust, standing up to 2 feet tall. Offset corms send up smaller plants below the mother, and cormlets may be divided from the parent and transplanted in late autumn. The fruit heads--clutches of scarlet berries, revealed as the spathe and leaves die back--lend vibrant color to the garden in fall. The fruits are consumed by birds, but all parts of the raw plant, suffused with needlelike crystals of Calcium oxalate, are toxic to mammals. The fruits may be broken apart and dispersed throughout the garden. A generous blanket of leaf mould will keep the seeds from drying out over winter and foster moisture retention in the soil.
A version of this article originally appeared in my monthly (more or less) column "The Wild Garden," in the Bloomington Herald-Times (4 August 2016).