Botany - Impatiens

Flowers Reproduction Leaves Roots Migration

Flowers

Impatiens or ‘Balsams’ come in a dazzling array of sizes, shapes and colors. Their colorful flowers may be their most remarkable property. Indeed, the only other plant family comparable to Impatiens are the Orchids. This is not to say that there is a direct counterpart for each species, but as a general rule they really do appear to be quiet close. What makes them similar is the way they evolved to appeal to a particular pollinator such as birds, bees, moths, and butterflies. With Impatiens, as well as most Orchids, the flowers are always zygomorphic and resupinate meaning that if the flowers were cut up like a pie, no two pieces would be the same or equal whereas if you took a composite-like flower and sliced it the same way, you would get an equal number of same sized pieces. Resupinate or resupination is the twisting of the flower as it emerges from its pedicle. In the case of Impatiens this is 180 degrees so what looks to be the upper petal is actually the lower.

All Impatiens have five petals and three or five sepals, with the lower sepal elongated into a spur in most species. The four lateral petals of the flowers are always united in pairs and to some appear to be one large petal. Many people identify easily with I. walleriana whose flowers are pretty much a flat disk like shape. This feature is fairly common with many species, but there are many other variations. For example the flowers can be lobed as in I. hawkeri and even lobed lobes as in I. bequartii and I. acaulis. These two species appear to have six lower petals giving the appearance of a star. Many other flower have unique shapes like, I. arachnoides whose tiny flowers look a lot like a Slipper Orchid when viewed from the front. Yet another variety is I. hians whose petals are so reduced that they look like narrow arms. Some species have very small side petals to where the lower petals make up most of the flower like I. cordata and I.hochstetterii. In I. niamniamensis the petals small that they just cover the spur.

The number of sepals in most species has been very reduced and typically are only three although some of the genetically older species still retain the five. The lower most sepal has been greatly modified and elongated into a nectar filled spur. The spurs in some flowers can be very showy like that of I. niamniamensis 'African Queen' with its candy corn colors are shaped for bird pollination whereas the spur in I. walleriana have evolved for moth and butterfly pollination. There is one group of Madagascar species (subgenus Trimorphopetalum) that have lost their spurs entirely.


Reproduction
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The basic structure of Impatiens is similar in all species. All have the same type of reproductive column that changes from male to female, and is stationed at the top opening to the lower sepal and spur. When an Impatiens flower first opens, the stamens are visible. The pollen can be very colorful with shades of white, red, or purple and has a fluffy, cottony look that easily flakes off. Within a few days on opening, the cap releases its grip and falls off to reveal the pistils and ovary beneath. Within a few hours, the pistils are receptive to pollen from another flower. In theory, this reproductive habit is to prevent or reduce self-pollination but, this is not always the case. For example there is the ever-popular Impatiens walleriana, that self sows very easily and the old Victorian standard I. balsamina. But some species seem to need another member of the same species to set seed, like the Madagascar species, I.tuberosa. The North American species on the other hand, have the ability to fertilize their flowers without ever opening up. The process is called cleistogamy or cleistogomous and is achieved in the bud stage; some times what is left of the petals still cling to the very tip of the pod.

Once the capsules are mature, they are held at great pressure and when touched will snap open throwing their little brown seed a great distance sometimes 20 feet from the parent. When ripe, the seed should be dark brown or tan, not white and should be sown as soon as possible because most species have a very short shelf life. Some of the annual species need to go through a season of cold and will come up in the spring.


Leaves
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The leaves of Impatiens are not, for the most part, remarkable. They tend to be a rather simple ovate to lanceolate shape with small serrated edges and green or bronze in coloration. Leaves can, depending on the species, be alternate around the stems, sometimes opposite, or come in whorls of three or more. Impatiens kilimanjari and I. catatii both have leaves that come in whorls of three, but in I. sodenii the leaves can sometimes can be in whorls of up to ten surrounding the thick succulent stems.

There are some species with remarkable leaf coloration and variegation. There is for instance the New Guinea Hybrids that have a stunning array of gorgeous coloration. The New Guinea Hybrids are to Impatiens what Begonia rex hybrids are to the genus Begonia. You can find some with whorls of electric yellow running down the center of the leaf. The most stunning may be the deep dark bronze leaves with mixtures of red, yellow, and orange markings swirling down the center.

Impatiens walleriana may be the most popular garden annual in the world but there are the little known variegates that are hardly known at all. These little gems are actually genetic mutants, and like many other variegated plants in the garden world they are often sports or offshoots of the plain green forms. Splashes of greens and grays with creamy yellow boarders dominate and some will have a layer of red and pink mixed in for good measure. Most of the variegated kinds available are the doubles that resemble roses; these are entirely sterile, will not reproduce by seed, and are only available as cuttings from named cultivars. Even more rare are the single forms, which are fertile and will set seed, but the seedlings often don't make it to maturity. The named forms are also only produced by cutting material from the parent plant.

There are a few variegated species out there, as well. One remarkable cultivar is the variegated form of I. niamniamensis “African Queen” or “Congo Cockatoo”. This sport is very beautiful, with quite large golden yellow leaves and a patchwork of green and gray markings. There are some with more subtle markings. Such as the little I. marienae with silver stripes that run down between the center of the veins, that reminds one of the aluminum plant (Pilea cadierei ). On a much larger scale is the rare Impatiens claeriwhich has large leaves with a narrow band of silver along the central vein. With its large leafy habit and tubular pink flower, this makes a wonderful specimen for the garden or greenhouse.


Roots
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Roots are not what most people are interested in when growing Balsams, but they are a very intricate part of how these plants survive in the wild. Most Balsams have a fibrous root system and are more susceptible to the environmental changes in which they grow, e.g. dry or freezing conditions. Some, notably the Asian species, have developed a tuberous root system which helps them survive these environmental hazards.

Impatiens arguta is a perfect example of a hardy Balsam. The roots are somewhat thickened and shoots don’t appear until after temperatures have risen above the freezing. This species is one of the tougher ones, taking both heat and freezing cold. This is by far the hardiest of the Impatiens I have grown.

Impatiens tinctoria has a similar type of root structure somewhat like a Dahlia, it has survived in sheltered gardens in Scotland. There are others from China like I. Omeiana and I. “Milo” that have a running type of rhizome. These roots travel though the loose soil of the forest floor and spring up at different points from knobby roots. Both these species can make quite a large colony when allowed to spread freely.


Migration
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The current flow of evidence points to Impatiens originating in Southeast Asia. The current idea is that Balsams developed in Southeast Asia and migrated overland into Africa at least twice in their history.

There are a few Impatiens that are genetically related to Asian species namely the Impatiens tinctoria group. This group reaches up into Ethiopia and does share one feature with many Asian species and that is, it still retains all five sepals. By contrast most African species have been reduced to only the basic three sepals. Impatiens were probably much more common in their prehistoric history when the world was a much wetter place. But as the world began to dry many species became isolated and some distinctive groups began to appear.

Impatiens do not, for the most part, come from hot steamy jungles in fact, many will not survive long, as they normally melt away in that kind of heat. Instead, a majority of Impatiens come from what are called montane forest areas. These are often mountains or hilly regions, sometimes called Cloud Forests or Highlands, and are high enough in elevation to have cool summers and fairly mild frost-free winters with a good supply of rainfall through out the year. The regions become, in effect, an island in the middle of the tropical jungle surrounded by a sea of heat. This ecological feature causes isolation of species that were at one time considered the same.

In the past Impatiens were more widespread, favoring the cooler climates. Over time the climates change and what was once easy passage for migration is now blocked by rising levels of heat in the lowlands. During the many millennia, this eventually has created new species. Through its long isolation this causes it to become endemic, occurring in just this one area and nowhere else, this is one of the main reasons why Impatiens are so endangered.

Not all Impatiens species are bound by this sea of heat, Impatiens walleriana has been found in many lowland areas and with the help of man has found many more. The annual Impatiens balfourii has many new homes in North America and Europe and seems to have adjusted to a Mediterranean climate very easily, taking the hotter dry weather extremely well. It will eventually die off by late summer, but not before putting on a big show and broadcasting innumerable seeds. Impatiens tuberosa has developed a caudex to survive the dry season in its Madagascar homeland. I have heard tell of this species naturalizing in some gardens in San Diego, coming up everywhere to the point of being almost a weed. One gardener in New Jersey has told me that it has come back as a reseeding annual. The tree-like Impatiens mirabilis hails from the Thailand low-lands and is often found in many a market place.