Plants With Weird Foliage: Window Plants

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Frithia pulchra, sometimes called baby toes, is one of many curious window plants. Source: venanaturale

Here is another article about plants with truly startling and unusual foliage, a short series I intend to add to from time to time. This article therefore follows Five Plants With Weird Foliage, Four Other Plants With Weird Foliage and Plants With Weird Foliage: Perfoliation. Just click on the links if you ever want to re-read them.

How Leaves Function… Normally!

Although there are nearly 400,000 species of plants on our planet, most have leaves with exactly the same structure. First, there is a dark green upper surface. Its color comes from chloroplasts, the green cells that convert sunlight into energy and are located just below the leaf’s upper surface. The underside of the leaf, though, has few chloroplasts and is therefore a paler green. This organization is very logical, because the plant’s goal is to capture a maximum of solar energy and the sun is located above the plant, not below. Even the way most leaves are held on the plant, that is, horizontally, is designed so they can absorb all the solar energy possible.

When the Sun Is Too Intense

So much for a typical leaf! But some plants, especially those of arid climate plants, face a rather unusual situation. The sun where they grow is so intense it can burn the leaves. Also, they can’t possibly absorb all the energy it produces. Most plants living under arid conditions have had to find some way of protecting themselves from the sun’s excesses.

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Many plants that grow in the extreme sun of arid climates, like this panda plant (Kalanchoe tomentosa), have leaves covered with protective hair or wax: Mother Nature’s sunscreen. Source: www.gardenia.net

These plants have different strategies to get around an overly intense sun. Sometimes the leaves are covered with wax or hair that reflects rather than absorbs light, sometimes the plant sacrifices its leaves entirely and photosynthesizes through its green stems (cacti are good examples of this) and sometimes the plant gives up entirely, losing its leaves and retreating into dormancy, often underground, during the hot season. But of all the adaptations to an overbearing sun, window plants have come up with the most fascinating adaptation.

Nature’s Skylight

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Most window plants, like this Lithops, grow nearly buried, with only the leaf tip showing. Sunlight penetrates the window and can easily reach the chloroplasts located all round the inside surface of the leaf. C.T. Johansson, Wikimedia Commons & cliparting.com

Most window plants pull themselves down into the ground during the summer, leaving only the tip of their leaves exposed. And this exposed part is not green, although it may look that way at first, but rather translucent, like a window. Thus, the intense and burning light penetrates through the tip of the leaf, but is then diffused by the gelatinous translucent sap inside and redirected to the chloroplasts which are located inside the leaf, near the outer walls, and therefore literally underground. It’s all rather like a skylight. The transparent leaf tip of window plants is rarely sharply pointed, as that could lead to water loss. It is rather truncated or rounded, as that reduces the surface exposed to drying winds.

This ingenious adaptation, which botanists call a leaf window, an epidermal window or fenestration, has evolved not once, but several times in different families. The best-known window plants are the living stones of the Aizoaceae family, a group which, broadly viewed, can be said to include Lithops, Fenestraria, Frithia, Ophthalmophyllum, Conophytum and several other genera. However, there are window plants in other families, including the Asphodelaceae, Asteraceae and Piperaceae families.

Curiously, the vast majority of window plants come from the same region: the deserts of southern Africa. What is not clear, though, is why. What is so special about the conditions in this region that stimulates plants to develop—independently!—a window rather than or in addition to other methods of surviving drought used by plants in other desert climates, such as succulence, summer dormancy, reduction of stomata and others? I’m sure someday botanists will find an explanation.

The Mother of All Window Plants

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Fenestraria rhopalophylla: the windows look like contact lenses!  Stan Shebs, W

The most windowlike of the window plants is undoubtedly Fenestraria rhopalophylla, in the Aizoaceae family. In fact, it is often simply called “window plant” in English (baby toes is the other common name) … and that’s also the meaning of its botanical name Fenestraria. This plant forms a rosette of upright pale gray-green tubular leaves, each capped with a rounded and completely translucent tip: it looks like it was wearing a contact lens!

In nature, only the translucent tip is visible, the rest of the plant remaining buried. When grown as a houseplant, we like to expose more of the leaf, partly to highlight the plant’s curious form, but mostly because it’s hard to imitate the intense drought and dry heat of its native country in our homes: if we bury the leaves the way they grow in the wild and the soil around them remains the slightest bit moist, the poor plant tends to rot.

 

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The other baby toes, Frithia pulchra, has leaves more truncated than rounded. Source: C. T. Johansson, Wikipedia Commons

Frithia pulchra, also in the Aizoaceae, is very similar, with the same tubular leaves and rosette growth, but this time the ends appear truncated rather than rounded. And the flowers are pink rather than white or yellow (the case with Fenestraria). This plant too is commonly called window plant or baby toes.

 

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Living stones grow nearly buried in the soil. The upper surface of the leaf is marbled with a mix of translucent and opaque patches, making it look like a stone or rock. Colors vary widely, according to that of the surrounding rocks. Source: Rudolf Marloth, Wikimedia Commons

The plants most often referred to as living stones are in the genus Lithops (Aizoaceae) and all have windows, but they are not as apparent as those of Fenestraria or Frithia because the window is marbled with paler opaque patches that mimic the coloration of the neighboring rocks.

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Lithops come in a wide range of colours. The darker patches are translucent windows, the paler ones, opaque tissues serving as camouflage. Source: worldofsucculents.com

Each living stone (and there are dozens of species) consists of two succulent half-moon leaves pressed against each other, plus a few roots. The leaves can be green, gray or even reddish.

Among other living stone genera that include species with windows are Conophytum and Ophthalmophyllum.

Mini Aloes

The genus Haworthia is closely related to the better-known genus to Aloe (both belong to the Asphodelaceae family) and indeed, most species look much like small aloes, with succulent leaves, a rosette growth habit and sharply pointed leaves.

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Haworthia cymbiformis obtusa has very striking windows.  Source: 賴永聰, pinterest.

Species with windows, such H. cymbiformis and H. retusa, sometimes called cathedral window haworthias, are different. They have leaves with a more rounded, translucent tip and in nature, live essentially underground with only that part of the leaf exposed.

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Haworthia truncata: the flat upper surface of the leaf is a window. Source: Stan Shebs, Wikimedia Commons

The most extreme window haworthia is H. truncata, sometimes called horse’s teeth. The end of each leaf is “truncate,” as per the species epithet truncata, meaning it looks like it has been cut off … with a saw. The leaf tip appears dark green, but is, in fact, translucent. This species usually grows in a fan shape rather than the more typical rosette common to haworthias. It’s a distinctly odd-looking plant!

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Most unusual and rarely grown, Bulbine haworthioides bares ground-hugging leaves with numerous translucent windows. Source: Jeffs-bulbesetpots, picssr.com

Another genus of the family Asphodelaceae, Bulbine, also produces a few window plants (notably B. haworthioides and B. mesembryanthemoides). Their succulent leaves form an entirely flattened, ground-hugging rosette marked with translucent patches. Curiously, many other bulbines have fairly ordinary succulent leaves, much like an aloe, and others have deciduous grasslike leaves and underground bulbs or tubers. They spend the dry season safely underground, fully dormant.

Cat’s Eyes

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Only when the leaves are backlit are you likely to notice the narrow windows on Senecio rowleyanus. Source: Green Lady, YouTube

String of pearls or rosary plant (Senecio rowleyanus), a popular houseplant in the Asteraceae (sunflower) family, is also a window plant, but its window is rather discreet. Its small leaves, almost as round as a pearl with just a small pointed tip, are medium green … but this is not the part of the leaf that carries out photosynthesis. If you look closely, you’ll see that each leaf has what looks like a darker green ray like a cat’s eye, but which is, in fact, transparent. It’s through this slit that the light penetrates the leaf and reaches the photosynthetic cells on its inner periphery.

This window often goes unnoticed and many people grow this fairly common succulent without realizing how truly extraordinary it is. The window is best noticed when the plant is backlit by sunlight and it then appears yellowish green and distinctly more translucent.

Unlike other window plants seen so far, string of pearls does not grow half-buried, but usually completely exposed. The rounded leaves are borne on long, thin, creeping or trailing stems and it grows as a groundcover in the wilds of southern Africa, its stems rooting where they touch soil. As a houseplant, it’s most often grown in hanging baskets as a trailing plant.

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You can barely make out the window on the banana-like leaves of  Senecio radicans. Source: mountaincrestgardens.com

The chain of bananas (S. radicans) is similar in habit, but, as the name suggests, its more elongated leaves look somewhat like bananas. String of beads (S. herreianus) fits in between the two. Its succulent leaves are somewhat rounded, yet more pointed than S. rowleyanus. Both have the same kind of very narrow slit-like window.

A Leaf in Prayer

The window plants we’ve seen so far all evolved independently in southern Africa, but there is one major exception.

In the vast genus Peperomia of the family Piperaceae, with over 1500 species distributed throughout the tropics, there is a handful of species of window plants, all from Peru and Ecuador. The logic behind their fenestration is not so clear as with the African succulents, because these peperomias don’t live in a desert environment, but rather in tropical forests, often as epiphytes. But they are succulents, with thick leaves that store water, something that can be useful to an epiphytic plant, given it has no soil to protect its roots from dehydration and is constantly exposed to drying winds.

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The leaves of the prayer peperomia (Peperomia dolabriformis) seem to be folded in half. The dark green streak on top of each one is the window. Source: plantsam.com

What is fascinating with the best known of these window plants, the prayer peperomia (P. dolabriformis, whose specific name means “shaped like a doloire”, a kind of axe) is that it seems to have been caught midway through its evolution, as if it weren’t quite finished. Just looking at the strange leaf, you can easily see that what was originally an ordinary elliptical and flat leaf has folded upward and inward, like a praying hand (the origin of the common name prayer peperomia) as if to protect its upper surface. What was originally the paler green back of the leaf is now borne upright with a slightly depressed window now separating the two halves. The window looks dark green, but is actually transparent and sunlight can travel through it to the chloroplasts lining the inside of the leaf.

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Peperomia graveolens. Source: public.fotki.com

There are other peperomias with a similar habit. This group includes P. nivalis and the very interesting P. graveolens, where the outside of the leaf is red and thus contrasts strikingly with the green window in the center.

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The narrow leaves of Peperomia ferreyrae don’t display their window too readily, but you can seem them if you look carefully. Source: Succulents.us

P. ferreyrae, with narrow, pointed, scimitar-like succulent leaves, seems to have evolved further than the others, because you no longer notice the effect of a leaf folded in half. Its windows are present, but quite discreet.

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Peperomia columella. Source: worldofsucculents.com

Finally, the most bizarre of all the window peperomias is undoubtedly the columnar peperomia (P. columella), a short, upright plant whose small, stubby, very succulent leaves look like they were chopped off at the tip.


The window plants are truly fascinating … and many of them make attractive, easy-to-grow, thought-provoking houseplants. Place a window plant in front of your window today!20180119C Eng C.T. Johansson, Wikimedia Commons & cliparting.com.jpg

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5 Plants With Weird Foliage

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There is fascinating foliage all around if you just make the effort to look! Source: Clipart Library

The whole point of a leaf is to collect sunlight and convert it via photosynthesis into sugars for the plant’s growth. Thus, a leaf simply has to be green to be functional. You’d think a simple flat shape would be enough, but no. There are as many leaf shapes as there are plants and they come in far more colors than they legitimately should. Here are some of the more interesting and memorable ones.

Swiss Cheese Plant (Monstera deliciosa)

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The Swiss Cheese plant has slits and holes much like Swiss cheese. Source: Forest & Kim Starr, Wikimedia Commons

This is a very common houseplant whose leaves just keep getting bigger and bigger … and weirder and weirder. If you’ve ever grown one from a young plant, you know the first leaves are entire and heart-shaped (the Swiss cheese plant is often mistaken for a philodendron at this point). Then, as it grows, the leaves get larger and splits start to appear. As the leaf increases in size, the number of splits increases and then holes (leaf perforations) start to show up. The leaf keeps increasing in size and, as it does so, more and more perforations appear. If you have the space for this huge plant (they don’t call it Monstera for nothing!), the leaves can reach nearly 1 meter (3 feet across) and will be strikingly beautiful … and weird.

As for why the leaves become so “tattered” (and I use that word in the nicest possible way), that’s a matter of conjecture, but I like the theory that it’s because large leaves are like a banner strung across a street: if you don’t punch a few holes in them, the wind will tear them. I’ll write more about this phenomenon in a future blog.

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The inflorescence of the Swiss cheese plant is spectacular, but rarely seen except on very mature specimens. Source: Karl Wimmi, Wikimedia Commons

The Swiss cheese plant is normally a climber and will grow best when offered a (sturdy) moss stake to cling to. It tolerates low light, but for big leaves, give it as much light as you can. This will also keep it more compact. You are allowed to cut off the numerous aerial roots it produces (I like to keep a few for show). It may even bloom for you one day, with sail-like white blooms (think of a Spathiphyllum). The fruit that follows is edible when it fully ripens and its scales start to drop off and, as the name Monstera deliciosa suggests, is sugary sweet. Other than the ripe fruit, though, the plant is poisonous.

The Swiss cheese plant is easy to grow indoors, but does appreciate good atmospheric humidity (to prevent leaf browning). Otherwise, just give it regular houseplant care … and be patient!

Cooper’s Haworthia (Haworthia cooperi)

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Haworthia cooperi’s window leaves can appear completely otherworldly. This is H. cooperi truncata, with rounded leaf tips. Other varieties have pointed tips. Source: 9gag.com

I’m using this plant as an example of a window plant. There are many others in such genera as Haworthia, Lithops, Peperomia, Senecio, Fenestraria and Frithia, but all have the same fascinating characteristic: they have a translucent area at the leaf tip where sunlight can reach down through the gelatinous transparent leaf interior and reach the photosynthetic cells along the outside edges lower down. This is exactly the opposite to how other plants function. Their photosynthetic cells are located near the outside of the leaf, not buried deep inside.

Most of these window plants come from very arid climates and essentially live underground, with only their leaf tips exposed, each acting like a skylight, allowing even the buried leaf parts to photosynthesis. When we grow window plants in pots, however, sometimes we grow the plant with the entire leaf exposed, partly to show off the leaf … and partly to prevent rot.

Window plants are yet another subject I’ll cover in more detail in a future blog, but for the moment, here’s what you need to know about Cooper’s haworthia.

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Haworthia cooperi cooperi has pointed leaf tips… but the same windows as other varieties. Source: Abu Shawka, Wikimedia Commons

It’s a small, easy-to-grow succulent that will do well on almost any fairly sunny windowsill. It produces offsets and slowly the original rosette fills in the surface of the pot with the new growths. Just grow it like any other succulent, watering only when the soil is quite dry, and you’ll have success. It will even bloom quite readily, although the flowers aren’t very showy.

To best appreciate the transparent beauty of the leaves, you do need to place this plant carefully: at about eye level, with the sun in the background. When looked down on from above, the windows are not as noticeable.

You’ll find it, or other window haworthias, in most garden centers.

Venus Flytrap (Dionaea muscipula)

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The traps of Venus flytrap lie on their moss bed, awaiting the visit of a spider or insects. Source: Mokkie, Wikimedia Commons

There is no denying the plant has weird leaves. Weird in appearance and weird in how they’re used. A broad, winged, often heart-shaped petiole rises from a small rosette and it carries on normal photosynthesis, while the leaf blade itself forms two lobes, each with a ring of teeth around the outside. When an insect or other arthropod triggers the mechanism by touching the small hairs in the center of the leaf, the leaves close quickly, trapping the creature, then the leaves produce gastric juices to digest it. Yes, this plant is carnivorous, or, to be more precise, insectivorous.

Like most insectivorous plants, the Venus flytrap developed its feeding habits because it normally grows in a very sterile environment, in this case, nitrogen- and phosphorous-poor bogs in North and South Carolina. It needs insect “meat” to supplement its meager diet.

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Remove the plastic container the plant is sold in and grow it in a sunny window sitting in a saucer of rainwater. Source: www.carnivorousplants.org

Although widely sold as a houseplant, the Venus flytrap is more of a curiosity than a good indoor plant, nor will it thrive outdoors under garden conditions unless you can recreate the environment of a cold, but nearly frost-free bog (zoned 7 to 9).

In most cases, it’s best to think of this plant as a temporary one, something to be tossed when you’re finished with it.

You can keep a Venus flytrap growing for years, though, if you know what to do and are willing to bow to its whims. Read more about it in No Hamburger for the Venus Flytrap.

Mother and Daughter Croton (Codiaeum variegatum forma appendiculatum)

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Actually, with their amazing colours and strange shapes, all croton leaves are quite weird. Source: www.pahls.com

I suppose all crotons have weird leaves. Almost always variegated, they come in a wide range of colors (red, orange, yellow, purple, green and white), plus they change colors as they mature, so leaves from different parts of the plant may be very different colors. The leaf shape too is extremely variable, from ovate to linear and entire to deeply lobed, and often twisted or spiraled.

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Certainly the oddest of all crotons thanks to its leaf extensions is the mother and daughter croton. Here, the cultivar ‘Appendiculatum’. Source: www.thepaddocks.de

But the weirdest of all the crotons are those so-called called mother and daughter crotons: C. variegatum forma appendiculatum. In these, the leaf, often fairly linear, produces a narrow stalk from its tip, then a smaller leaflet, often curiously funnel-shaped, appears at the extremity. It looks like a kite on the end of a string!

I sometimes get letters from readers who think a baby plant is growing from the tip of a mother leaf. Sorry, but no dice: the croton is just not one of the plants you can grow from a leaf cutting, even less from a leaf section. You’ll need to take stem cuttings (or air layer the plant) to multiply it.

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Croton ‘Interruptum’. Source: piergrossi.squarespace.com

There are only a few cultivars with the appendiculatum habit, one being called just that: ‘Appendiculatum’. It has green leaves, although there is also a red form bearing the same cultivar name. The other often seen is ‘Interruptum’, with green leaves mottled yellow turning into red leaves mottled orange. Never is a very common plant. Unless you have a croton nursery in your neighborhood or can order one by mail, you’ll just have to wait until one of these curious mother and daughter crotons shows up in a garden center near you.

The croton has the reputation of being a persnickety houseplant, but I have specimens over 20 years old and they do just fine. Of course, I lost more than a few until I figured out that what they really need is high humidity until they settle in. Ideally, buy them in late spring or summer, when the air is naturally humid, and put them in their permanent spot, which needs to be a brightly lit one. By the time the dry air of fall arrives, they’ll have had time to adapt to your conditions and should do fine. Other than that, basic houseplant care is all they need … but do keep them out of cold air (less than 60˚ F/15˚ C).

Crotons also make great outdoor shrubs and even hedges, but only in truly tropical climates (zones 10 to 12).

Ginkgo (Ginkgo biloba)

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Ginkgo leaves are totally original: you can never mistake them from anything else! Source: www.edenproject.com

Most really weird leaves are found on tropical plants, which is normal considering the vast majority of plants on this planet are of tropical origin, but there are still many leaf oddities among hardy plants and I think the ginkgo clearly merits a spot in the list of weird leaves.

Maybe you’ve seen ginkgoes around you so often they’ve come to seem quite ordinary to you, but their leaf shape is in fact unique among seed plants. Only maidenhair ferns (Adiantum spp.) have leaflets anything like them.

Each leaf has a very special fan-shaped form, caused by veins that split in two, then split in two again and again. It’s as if the needle of a pine started out narrow, then became increasingly crested from the mid-point on. And ginkgoes are indeed gymnosperms, closer relatives to conifers than to flowering plants, in spite of their broad leaves and deciduous habit.

250 million years ago, ginkgoes were the dominant trees on our planet and were apparently a major food source for dinosaurs. There is only one species left, G. biloba, rarely found in the wild and even then only in isolated areas of Southwestern China. However, it is now grown as a cultivated plant the world over in hardiness zones 4 to 9.

The ginkgo is a very slow-growing but forgiving tree, adapting to just about every condition as long as drainage is good.

More Weird Leaves to Come

20171130A Clipart Library.jpgI’ve only scratched the surface of plants with weird leaves. I have many others I want to present to you and hope to do so over the coming months. Also, I’m looking for suggestions. Maybe I’ll be able to include your choice in one of the future blogs! If you allow me to use one of your photos, I’ll add that too! Just write me at horticom@horticom.ca.

Do note I’m looking for plants that repeatedly produce odd leaves, nor for a single mutant leaf on an otherwise normal plant, nor do leaf oddities provoked by insects or diseases count (although I have to admit some leaf galls are pretty amazing!). Also, for the moment, I’m sticking to leaves, not weird growth habits or weird flowers.

Thanks for any help you can offer!