Part of what makes this plant so intriguing is the many different common names by which it is known: Mother of Thousands, Mother of Millions, Alligator Plant, Mexican Hat Plant, Devil's Backbone, Piggyback Plant (or Pick-a-back Plant, depending on the region), Panda Plant, and Maternity Plant. Its scientific name is Kalanchoe diagremontiana, though it is also sometimes classified as Bryophyllum daigremontianum. It is native to the mountains of Madagascar, which stirs my curiosity. I wonder how it came to be a common house plant, so far from home!
This unusual specimen is a fleshy succulent with narrow, pointed, serrated "leaves" forming in opposing pairs on alternating sides of the fleshy, flexible stems. The leaves are generally green on the upper surface, and either a lighter green, or green streaked with purple on the lower surface. These are actually not really leaves at all, but rather leaf-like stems known as phylloclades or cladodes. All along the edges of these "leaves" are little jagged spurs, which have the unusual ability to asexually develop little plantlets on each point, complete with two pairs of leaflets and roots. These little plantlets are genetically identical progeny, since there is no cross-pollination with other plants involved.
As a child, I was particularly fascinated with these tiny plantlets. This form of vegetative propogation isn't terribly common in the plant world, though it is by no means unique to this plant. I loved to "zip" the little baby plants from the leaves and press them into the damp surface of the soil after watering the parent plant. If I allowed them to stay on the leaves long enough undisturbed, they would actually begin forming roots, and then drop from the leaves to the soil of the pot (or into other plants on her shelves below, where they would quickly colonize the neighboring plants' pots as well.)
The stem of the mother plant wasn't very rigid, and as the upper leaves got larger and heavier, they would cause the stem to form interesting curves and bends, often draping lanquidly over the edges of the pot. If the stems touched the soil, roots would quickly form there as well. Even if a curve dipped NEAR the soil, roots would form on the lower edge of the curve and begin reaching for the surface. After a while, new stems would begin to grow from the roots, forming a new plant alongside the original parent plant.
I have never seen a Kalanchoe daigremontiana flower, though as I researched it for the article, I learned that they do occasionally send up an umbrella-like stalk with a cluster of downward facing pink or purple bell-shaped flowers. These flowers, however, do not produce viable seeds. As with many succulents, the bloom appears to be the last gasp before the plant dies, often in the autumn. There are several pictures of the blooms submitted by Dave's Garden members available on the Plant Files entry, which is available by clicking here.
When I looked the plant up in Plant Files, I was surprised to see the many negative ratings associated with its prolific tendency to spread. Apparently, I am fortunate that I live in a climate cold enough in the winter to require me to keep my Kalanchoe in a pot indoors. I have limited space, so mine tends to be relegated to a fairly small pot that doesn't give it much encouragement to grow rapidly. It resides in a clay pot, in succulent potting soil with fairly sharp drainage. It thrives without frequent watering, which makes it an easy houseplant for a busy household like ours. Even with my benign neglect, I've noticed new sprouts popping up in other pots, where they've dropped from the mother plant. I've had difficulty removing them from my beloved Christmas cactus, and have since relocated the little offender to a location more removed from my favorite plants. Upon further research, I've learned that it not only colonizes the pots of other plants, but also negatively affects their growth, and can leave a residue in the soil that reduces the rate of growth of other plants.  It even suppresses the growth of its own plantlets, which I suppose is one method of encouraging the kids to move out of the house!
When planted outdoors in a more temperate climate, however, the plant ceases to be cute, and becomes a terribly invasive thug. Given its ideal warm, somewhat dry growing conditions, the plant can shoot up to 3 feet (approximately one meter) tall, and drop plantlets at an alarming rate. Each new plant then forms scores of plantlets along each of its leaves, compounding the problem if not eradicated quickly. It has been listed as a noxious invasive in many arid areas worldwide, including Texas, Florida, and parts of California in the United States, and Puerto Rico, Australia, Venezuela, South Africa, and parts of the Caribbean, among others.
Even in my climate and limited houseplant environment, I've discovered another cause for concern. I had decided to move my Kalanchoe to the kitchen, as it seemed to be yellowing and shriveling a little in the cool conditions of our sunny enclosed porch during the winter months. I set it in a north-facing kitchen window, where it did indeed begin to return to its former rich green color. My husband noticed, however, that the plantlets were dropping from the leaves and landing in our dog's bed below. He asked if it was dangerous if she would happen to eat one. When I looked it up, I was alarmed to see that all parts of the Kalanchoe is, in fact, highly toxic. It contains the cardiac glycoside daigremontianum, which can even be fatal for small children and pets, so exercise extreme caution if you decide to grow this plant. In the wild, it presents a very real danger to grazing livestock and wildlife. Once I knew of its toxic properties, I decided it was safer to keep it behind closed doors on the chilly enclosed porch, where my pets wouldn't be able to access it. If I had to chose between losing a plant or losing a pet, the plant would have to go!
 Botanical Gazette, Vol. 136, No. 2: 207-211. June 1975, "Allelopathic Influence of Kalanchoe Daigremontiana on Other Species of Plants," by Miriam G. Groner. 1975 University of Chicago. (http://www.jstor.org/discover/10.2307/2474132?uid=2129&uid=2&uid=70&uid=4&sid=21101528344103)
To read more about Kalanchoes, see this article, by PalmBob: http://davesgarden.com/guides/articles/view/2673/
All images in this article are my own. Please do not copy or distribute them without permission. All rights reserved.