I’m writing a series of blogs about plants with weird foliage, blogs that will appear occasionally, according to the time I have to write them… and my whims. Two previous articles have already appeared: you can read them at 5 Plants With Weird Foliage and 4 Other Plants With Weird Foliage.
I’m dedicating today’s blog more to a type of foliage than to the plants themselves: perfoliate leaves.
The Conjoined Twins of the Plant World
Most angiosperm leaves – probably over 95%! – are attached to their stem by a short stalk called a petiole (or leaf stalk). They’re said to be petiolate. Most of the remainder are sessile – they attach directly to the stem, with no petiole – and others yet wrap partly or entirely around the stem and may be said to be clasping or sheath leaves. But the oddest situation of all is when the leaf forms right around the stem, to the point where the stem appears to grow right through the leaf. These leaves are said to perfoliate.
The word perfoliate comes from modern Latin perfoliatus, from Latin per- (through) and foliatus (leaved). It thus literally means “with leaves that are pierced.”
Most perfoliate leaves evolved when a pair of opposite leaves gradually fused together. This is the case with the giant perennial, Silphium perfoliatum, called the cup plant, because rainwater often accumulates in the depression where the two leaves join. With this plant, you can still clearly see that there were originally two leaves that joined together, but many perfoliate leaves have so clearly merged that they appear to be one single, often round leaf.
Not all perfoliate leaves derive from opposite leaves fusing together. Sometimes a single leaf not only wraps around the stem (it’s said to be clasping or amplexicaul), but its base extends outwards until it takes on the appearance of a single leaf stabbed through the heart by a stem. Thoro wax (Bupleurum rotundifolium), an attractive if rarely grown annual, is in this group.
There and Back Again
Oddly, many plants go back and forth from perfoliate leaves to more classical petiolate or sessile leaves over their lifetime. Many eucalyptus trees, like spinning gum (Eucalyptus perriniana), have perfoliate juvenile leaves, yet willow-like, opposite, stalked adult leaves. If you prune a mature branch back, new juvenile perfoliate leaves will appear… for a while.
Likewise, many climbing honeysuckles, including Lonicera sempervirens (see the photo at top of this article), produce perfoliate leaves on their flowering stems, but opposite, stalked leaves elsewhere.
It Happens in the Best of Families
Perfoliate leaves evolved separately in different plant families (Apicaceae, Asteraceae, Caprifoliaceae, Colchiaceae, Crassulaceae, Fabaceae, Montiaceae, Myrtaceaeae, Plantaginaceae and many others). I won’t hazard a guess as to why they evolved and there are probably dozens of reasons why a perfoliate leave could be useful in some circumstances and not so much in others.
Perfoliation is still a fairly unusual trait, one botanists certainly notice, which is why you’ll find that many plants with perfoliate leaves have perfoliata, perfoliatus or perfoliatum as their specific epithet. It’s often the most obvious distinguishing feature between two otherwise similar species.
Perfoliation in Your Garden
Among the most widely available temperate-climate plants with perfoliate leaves are miner’s lettuce (Claytonia perfoliata, syn. Montia perfoliata), a quick-and-easy though little-known vegetable, the aforementioned cup plant (Silphium perfoliatum), becoming quite popular as a perennial for the back of the border, and several of the climbing honeysuckles. Common teasel (Dipascus fullonum), often a weed, but sometimes grown as an ornamental, likewise has perfoliate leaves.
In mild climates, several perfoliate eucalypti are widely grown.
Indoors, or for mild arid climates, string of buttons or necklace vine, Crassula perforata, comes in various forms, from densely stacked and upright to loose and trailing and all have perfoliate leaves. You ought to be able to find at least one type in any garden center. C. rupestris marnieriana is similar, with smaller, fleshier leaves.
Much rarer and very much weirder is the umbrella crassula (Crassula umbella) with distinctly umbrella-shaped leaves, sometimes wine-red underneath (cultivar ‘Wine Cup’). Extremely odd! Trying growing this one from seed.
Grow crassulas as you would any houseplant succulent: intense light and moderate waterings.
The Button Plant Clan
I’m not sure that conophytums (Conophytum), also called button plants, really qualify as having perfoliate leaves, as there is certainly no leafy stalk that grows through what are really two leaves fused together… but there is a flower, which seems to sprout magically smack dab in the center of what appears to be single buttonlike leaf.
As the author of this text, I figure I get to choose, and hereby declare conophytums perfoliate for the purpose of this article. And I think conophytums are simply the most fascinating of all the perfoliate plants.
Conophytums are among the many plants called living stones, all natives of southern Africa from the ice plant family, the Aizoaceae. Other living stones are found in such genera as Lithops, Fenestraria, Frithia and Pleiospilos and that’s only a partial list! All are ground-hugging succulents that survive a hostile, arid environment by camouflaging themselves as stones. Not all of the some 100 conophytum species are buttonlike, though. In fact, many bear pairs of cone-shaped leaves, whence the genus name Cono (cone) phytum (leaf). Still, over a third of them are distinctly buttonlike.
Conophytums may be cute as a button, but growing them is not so easy. Read more about them here: Growing Button Plants.
Perfoliate leaves: weird enough to star in science fiction movies, yet common enough to be found in most environments if you look carefully. Keep your eyes peeled!