The Azolla fern isn’t much to look at. It has tiny leaves and floats en masse on top of water . Many people consider it a watery weed: it can cover the entire surface of a lake or pond, choking off sunlight to other water plants. No one thinks swimming with Azolla is fun.
But Azolla is a miracle plant. The Scientific American just reported that 55 million years ago (ten million years after the end of the dinosaurs), when carbon dioxide levels were much higher than today and the Earth was much warmer, the Azolla fern came to the rescue. The Arctic Ocean was a big inland lake at the time, hot and overloaded with nitrogen. The evidence is that the fern grew abundantly in the lake, and when the seasonal rains fell, the Azolla spread out over the surrounding continents. As the ferns photosynthesized and grew, they sucked up carbon dioxide from the atmosphere in great quantities. During dry spells, the ferns died and their remains (and their carbon components) settled onto the land and became buried under sediment. This boom and bust cycle went on for a million years, and during that period, atmospheric carbon dioxide levels dropped by roughly half. Author Jennifer Huizen raises the question of whether Azolla might play a role in countering global warming today.
That’s not the only great thing about Azolla. I’ve been digging into algae (sometimes literally) and discovered that rice, Azolla, and algae are linked. Paddy farmers plant Azolla in the water next to rice plants. The ferns have symbiotic blue-green algae that help the ferns absorb nitrogen. The nitrogen is passed along to the rice plants, increasing their productivity significantly.
There are more great things to be said (and I will say them next week) for Azolla. But let me say this: It’s a weed we need!
In Holland between 1634 and 1637, tulip bulbs that produced flowers with irregular stripes, streaks, and feathery patterns cost thousands of dollars. But those who bought the tulip bulbs in this era of tulipomania were regularly disappointed. They discovered that the seeds of the bulbs didn’t produce tulips that were “broken,” as these bi-colored flowers were described. Moreover, each season, the bulbs’ flowers were fewer and weaker. Although the little bulbs that grew off the parent bulb (called offsets) produced broken flowers, the next-gen bulbs were always less productive than their parent.
It turned out that the source of the spectacular patterns was one of the dozen tulip viruses. Unfortunately, the virus weakened the plant, and ultimately the genetic line of a bulb would die out.
In the early 1980s, the Dutch government outlawed the sale of virus-infected tulips. But the flowers pictured here are not illegals. Today’s tulip breeders have manipulated the genetics of tulips to produce patterns, so you can buy bulbs that produce flowers that recall the seventeenth-century beauties, but will bloom exuberantly for many years.
This is the season for Robert Frost’s beautiful “Nothing Gold Can Stay”:
“Nature’s first green is gold,
Her hardest hue to hold.
Her early leaf’s a flower;
But only so an hour.
Then leaf subsides to leaf.
So Eden sank to grief,
So dawn goes down to day.
Nothing gold can stay.”
For me, the poem captures how swiftly we humans leave behind our completely innocent childhoods and move into more knowing adulthood.
In a botanical sense, though, Frost got it wrong. The yellows (as well as reds) that he sees in early spring leaves come from the carotenoid and anthocyanin pigments that are always in the leaves. In spring, the green chlorophyll pigment develops and soon dominates, and we can no longer see the other hues. Nonetheless, those colors are still there, which means that the gold does stay. This fact becomes apparent in fall after chlorophyll disintegrates and the yellow and red hues are visible again. My interpretation? Innocence and its close attendant, wonder, never leave us, even if they are harder to access in our maturity.
My book group read Rebecca by Daphne du Maurier this month, and we were all surprised by the descriptions of deeply fragrant azaleas at Manderlay in Cornwall. Around Washington, DC, the azaleas we know, while beautiful, are unscented. Why?
Azaleas are members of the rhododendron genus, and are closely related to the woodland rhododendrons. Most azaleas with scent are deciduous, so they lose their leaves in the fall. Most unscented azaleas are evergreen. Around Washington, DC, azaleas are often used as foundation-hiding plantings, so the evergreen (and therefore unscented) varieties are more popular.
About 1900––a few decades before du Maurier wrote Rebecca––Lionel de Rothschild fell in love with deciduous azaleas and bred his own cultivars at his Exbury estate in Hampshire (not far from Cornwall.) Some of the “Exburys” are particularly fragrant, so the second Mrs. de Winter may well have been entranced by Exburys.
This year, we lost a number of backyard shrubs to a particularly cold winter. I’m looking at deciduous azaleas as replacements. Not only do they provide fragrance, their leaves turn shades of bright orange, yellow, and gold in the fall.
“Leaves of three, let it be”: that’s the old mnemonic warning for avoiding poison ivy. Spring is the worst season for running into the plant, or rather the sap it carries in the cells of its leaves. That’s because the new leaves, which are often reddish, are particularly thin and fragile. A light touch can breach the cells, releasing the toxic urushiol inside.
For those of us on the East Coast who curse the white-tail deer for browsing our gardens, decimating forest underbrush, and make driving hazardous, we can thank them for one thing. Deer are unaffected by poison ivy oil, and happily chow down on the leaves.
In my yard in suburban Maryland, hellebores are the first of the spring flowers. This year, despite the unusually cold weather, they were up as early as ever. Even so, I know they’ll be in bloom for weeks and even months. What makes them such persistent bloomers?
For one, their petals are not really petals. They’re colored sepals, the leaves that cover and protect a developing flower bud. Because sepals are tougher than petals, they last longer. After the flower has been fertilized, the sepals’ pigments decay and the green pigment, chlorophyll, becomes evident. The longer the green sepals persist, the bigger the plant’s seeds. That’s probably because the sepals are photosynthesizing, enabling the plant to gather more solar energy and make more carbohydrates.
So, where are the hellebore’s petals? They have evolved into the little green leaves you can see at the base of the many stamens. (There can be up to 150 per flower.) The little leaves are known as “honey leaves,” and are actually nectaries that lure insect pollinators. No same old, same old about hellebores.
One of the most interesting and easy plants for cold climate gardeners is the Coffea arabica. I’ve had a potted one for years. It lives in a shady spot in the backyard in summer. In the colder months, I move it indoors to an east-facing window. Last May, per usual, my tree (about five-feet tall because I prune it regularly) produced a crop of small, white flowers. Nine months later, I have very ripe coffee cherries. (You can see the remains of the flowers at the tips of the cherries.) Inside each cherry are two coffee beans, which are the seeds of the coffee plant.
I’ve never tried to roast the beans (too much trouble and a home oven isn’t great for roasting coffee), but yesterday I tested a cherry. There’s not much pulp on it, but what there is, is deliciously sweet. In countries where coffee is grown, sometimes the pulp is dried and used as a tea. The tea, called cascara, is rich in antioxidants. Now, a Hawaiian company called Kona Red is producing a coffee berry juice. Last week, Walmart began offering the juice in 2,100 of its stores. I may have a new use for my next crop!
This lovely drawing by Eva-Maria Ruhl is a family portrait of the Leyland cypress (in the middle), that ubiquitous suburban conifer. I was delighted to write a guest rant for Gardenrant.com, and let off some steam about Leylands, or rather the way they’re misused in landscaping.
The Leyland is the offspring of two venerable North American conifers native to the West Coast, the Monterey cypress (on the left) and the Nootka cypress (on the right). The pair never would have met in their native habitats: The southernmost Nootka grows 400 miles north of the Monterey. But in the late 1800s, Christopher Leyland, a wealthy English banker, gave his nephew John an estate in southern Wales as a wedding present. John’s landscape architect installed a variety of exotic trees, including a Nootka and a Monterey. In 1888, the seed of one species and pollen of the other had a sexual encounter, and a hybrid seed sprouted.
When John’s son Christopher inherited the estate the next year, he cultivated the hybrids. Christopher Leyland’s seedlings prospered and became known as the Leyland cypress (Cupressus x leylandii). Leylands are sterile, but they are readily grown from cuttings. The problem is that suburbanites, in hopes of quickly creating a privacy screen, usually plant the saplings far too close together. As they grow taller (and they can add three feet per year), they shade one another, and become distorted and spindly and downright dangerous.
Stems come in all shapes and sizes, and some of them are eminently edible. Take the potato, (which I can do only if I add lots of butter.) The potato is actually a “stem tuber,” a stem that stores energy in the form of carbohydrates.
Potatoes differ from “root tubers” such as carrots, radishes, and sweet potatoes. The “stem-ness” of the potato is evident when you look into its eyes. The eyes are actually axillary buds, just like you find on the nodes of above-ground stems. When the eyes grow out, they form shoots, which then branch and sprout leaves. Cut up a potato and plant pieces that have eyes, and each one can grow into a new potato plant. Root tubers, on the other hand, are for storing energy, and have no buds.
A potato plant also produces flowers that range from white to pink and red to blue and purple. Some varieties produce green fruits about an inch in diameter. The fruits are poisonous, which is not too surprising since the potato is a member of the Solanaceae family, which includes deadly nightshade, henbane, mandrake, and other toxic “witches’ weeds.”