Species of the Week
Number 13 -- August 28, 2006

In the Species of the Week feature of the Wildwood Web we took a close look at one of the species that lives in Wildwood.  To see the earlier featured species check the Species of the Week archives.

Jewelweeds Impatiens capensis and Impatiens pallida Jewelweeds, also known as touch-me-nots, are great fun.  Find a seed pod that's ripe; that's easy because they swell up and look quite fat.  There's one hanging to the left of the lower leaf in the picture at left; two others, not yet ready, are dangling on the right.  Now, ignore the name touch-me-not and touch this ripe pod gently.  It will suddenly explode, peeling back the outer skin and flinging the seeds willy-nilly.  It's especially fun to introduce this phenomenon to a young child who has never met jewelweed before.  As the plant is an annual, this is clearly an adaptation to spread the seeds for next year.  When the pods are ripe even a good breeze can cause them to explode.  The common name, touch-me-not, obviously refers to the explosive fruits.  So does the genus name, Impatiens, from the Latin for "impatient."

Two species of jewelweed or touch-me-not are found in Wildwood.  In fact, both of them grow together at the bottom of the Grand Staircase.  Impatiens pallida, pale jewelweed or pale touch-me-not (above), has yellow flowers with a few red-brown spots.  Impatiens capensis, spotted jewelweed or spotted touch-me-not, (below) has orange flowers with red to red-brown spots.  Both have egg-shaped, toothed leaves, although pale jewelweeds leaves are a bit bigger.  Old-fashioned garden impatiens, also called Bizzy-Lizzy, is Impatiens balsamina; although modern cultivated impatiens are mostly hybrids

The species name, pallida, simply means "pale."  The species name capensis, though is a bit more interesting.  It means "of the Cape" and refers to the Cape of Good Hope at the south end of Africa.  As both species are native Americans, it seems odd that spotted jewelweed should be named after a location in Africa.  The botanist who named it was under the mistaken impression that it had been imported to European gardens from Africa, rather than from America, and the rules of botanical nomenclature do not allow changing a name merely because it doesn't fit.

Jewelweed flowers are very interesting.  They dangle like little earrings (hence, jewelweed?) under the leaves.  To me they look sort of like little rock lobsters with their tails tucked under them.  The flowers have three sepals and three petals, but all are brightly colored.  The three petals form the face of the flower, one large one sticking up and two hanging down in front.  Two of the three sepals are small and are found to either side of the top petal.  The third sepal is big, shaped like a sack, and tapers to a thin tail, called a spur, that bends backward under the flower.  Examine the lowest flower in the picture at right to see the spur.  The spur is full of sweet nectar.  If you are used to the rule that dicot flowers have 4 or 5 parts while monocots have 3 or 6, you will perhaps be perplexed to learn that jewelweed is a dicot.  Apparently someone forgot to explain the rule to the jewelweeds.

Interestingly, the flowers undergo a sex change.  When they first open they are male, but later change to female.  How can you tell their sex?  Look into the opening of the flower.  If you see white pollen, it's male.  If you see a little green pin, it's female.  The green pin is the tip of the female pistil waiting to receive pollen from another plant.  A hungry insect visiting a male flower will land on the landing platform formed by the two lower petals, and press inward, seeking the nectar way down inside the spur and getting dusted with pollen.  If the same insect later visits a female flower it will brush against the pistil as it squeezes inward in search of nectar, and deposit pollen upon it.  Some insects, however, have evolved to rob the poor jewelweed; they chew holes in the spur and suck the nectar out without the bother of pollinating the flower.  The showy, nectar-filled flowers we are discussing are formed during the lazy days of summer.  Later in the season, with frost approaching and the sunshine reduced, the plant will make small flowers that have no petals or nectar and never open.  Instead, these flowers will self-pollinate and produce seeds.  These late season flowers are easy to make, in terms of energy needed; however, the more expensive summer flowers have the advantage of increasing genetic variation among the offspring.

Jewelweeds are plants of moist woods, brooksides and seeps.  Their stems and leaves are juicy and succulent.  On the hotter days of midsummer the plant will wilt from water loss, but will revive when the air cools.  Most plants  close their stomata, the microscopic openings through which leaves breathe, when they are hot, to prevent water loss.  I have heard, though I do not know if it is true, that jewelweeds do not do this preferring, instead, to let the water evaporate, cooling the plant in the same way our sweat cools us.  Obviously, only a plant that lives in wet areas can adopt that strategy.

The sap from the plant is supposed to stop the itching of poison ivy.  I have never tried this myself, but I've seen it claimed in so many books, I suspect it may be true, at least for some people.  I'd be interested to hear from anyone with actual experience with this.

Jewelweeds are in the family Balsaminaceae, the Jewelweed or Touch-me-not Family.  There are about 40 species in the family, all but one in the genus Impatiens.  Most members of the family live in south Asia, particularly in India, and south Asia is where the cultivated species originated.  The two species in Wildwood Park are native to the eastern US and a few more species are found in the western US.  Cultivated plants sometimes produce seed that comes back wild the next year, but they are not a weed around here.  Tropical countries are another story, and I have seen big patches of weedy garden impatiens spreading deep within the forests of O'ahu and Puerto Rico.

Jewelweeds are annuals.  This is hard to believe sometimes, when you come upon a thicket of jewelweeds four or five feet tall.  All that grew from seed this year?  However, stop by the park after the first frost and you will find all the thickets of jewelweed dying, for they are very frost tender.  The seeds they flung out so wildly in the summer are cold-hardy and will wait until next year.  In the spring look for the pale green fleshy leaves of young jewelweeds coming up, and know that more jewel-like flowers and explosive seedpods will be found again in mid to late summer.

GGC