Category Archives: Plants

Living flypaper

On the edge of a mountain bog in Maine, a thumbnail-sized plant grows amid the mosses:

sundew

This is sundew, Drosera, a carnivorous plant, ready to ambush.

Darwin devoted twelve chapters of his 1875 book, Insectivorous Plants, to the anatomy, behavior, and physiology of a European species of Drosera. He writes:

During the summer of 1860, I was surprised by finding how large a number of insects were caught by the leaves of the common sun-dew (Drosera rotundifolia) on a heath in Sussex. I had heard that insects were thus caught, but knew nothing further on the subject… I gathered by chance a dozen plants, bearing fifty-six fully expanded leaves, … it was soon evident that Drosera was excellently adapted for the special purpose of catching insects, so that the subject seemed well worthy of investigation.

The results have proved highly remarkable; the more important ones being—firstly, the extraordinary sensitiveness of the glands to slight pressure and to minute doses of certain nitrogenous fluids, as shown by the movements of the so-called hairs or tentacles; secondly, the power possessed by the leaves of rendering soluble or digesting nitrogenous substances, and of afterwards absorbing them; thirdly, the changes which take place within the cells of the tentacles, when the glands are excited in various ways.

We now know that sundews are forced into a carnivorous mode of existence by the poor soils of the bogs in which they live. They are starved of nitrogen and, not being able to find any through their roots, resort to feasting on flying nitrogenous sources, aka insects. (If extra nitrogen is added to their roots, they back off from carnivory.) The “dew” on the plants’ leaves is sweet and sticky; the droplets lure and trap passing sugar-seekers. The plants’ movable hairs and leaves then draw their victims into the center of the rosette of leaves where glands digest then absorb the meal.

Insects also serve as pollinators of the sundew’s flowers. You’ll note that the flower stalks holding opening buds in the pictures above are very tall. Natural selection evidently says: don’t eat your pollinator for lunch.

My camera could not capture the full beauty of the sundew’s leaves. The following photo by “I, Petr Dlouhý” (generously shared under a Creative Commons license) gives a glimpse. The last thing a gnat sees before The End:

Drosera_rotundifolia_leaf

Guest post: Callie Oldfield on roadside management of rare plants.

I’m reposting an article by Callie Oldfield, a former student of mine who now works in Sewanee’s Herbarium. She describes a new collaboration between the University’s Land Manager, Nate Wilson, Physical Plant Grounds Supervisor, William Shealy, and the state agency charged with “roadside maintenance.” Many interesting and rare plants grow in the open spaces along roadsides and under powerlines. Too often they are drenched in herbicide or pulverized by mowing before they can set seed. So I was delighted to hear of my colleagues’ work and very happy to learn that other states are interested in the results of their program. I’ll let Callie continue…

TDOT and Sewanee work together to protect endangered plants on Cumberland Plateau

by: Callie Oldfield — November 04, 2015

Domain Manager Nate Wilson and PPS Grounds Supervisor William Shealy help design new management practices to protect native and endangered wildflowers growing in road right of ways.

Sewanee and the Tennessee Department of Transportation (TDOT) have been working together to protect rare plants and native wildflowers that grow along roadsides in the Sewanee area. Typically, plants growing roadside are mowed and sprayed with broad spectrum herbicides in order to prevent their growth into the road area. These herbicides eliminate the trees that pose the greatest safety threat, but they can also kill forbs and herbs, including endangered species such as Cumberland rosinweed (Silphium brachiatum).

Cumberland rosinweed is a south Cumberland Plateau endemic in the daisy family. Cumberland rosinweed can be found along US Hwy 41A, which runs through the Domain and state-protected natural area Hawkin’s Cove; this natural area was acquired by the state in 1985 in order to preserve its habitat. Other rare and unusual plants that have been subject to right of way spray in the past include: eared goldenrod (Solidago auriculata), Morefield’s clematis (Clematis morefieldii), cylindrical blazing star (Liatris cylindracea) and cut leaf prairie dock (Silphium pinnatifidum).

Domain Manager Nate Wilson and PPS Grounds Supervisor William Shealy helped spearhead this initiative to protect native wildflowers through designing new management practices. Sewanee made two recommendations: First, to allow TDOT to go off of their road right of way and into roadside Sewanee property to prune trees in a more aesthetically pleasing way that also lessens the tree’s tendency to exhibit vigorous regrowth, and second, to design a new herbicide spray formula that targeted the problem woody species while promoting grasses, forbs, and wildflowers.

For 6 months, Nate worked with a TDOT botanist and a DOW Chemical Company representative to come up with a new herbicide formula that will target only trees, because “trees are the threat [to the roads], not the grasses or forbs we are trying to protect.” The new formula will deaden only the portion of the trees touched by the spray and prevent that part of the tree from producing leaves in the spring, but will not harm forbs or herbs. As a result, fewer trees will need to be chopped or mowed, and our endangered species and native wildflowers will be protected.

TDOT sprayed this herbicide in the Sewanee-area for the first time last month and is considering adopting the practice more widely in the future.

Photos courtesy of Mary Priestly.

Ghosts rise from forest duff

2015-07-13 indian pipe monotropa 018Ghost plant, Monotropa uniflora, is now flowering in shaded woodlands. The species is also known as Indian pipe or corpse plant. Each stem is about finger-high and has a nodding flower at its tip. The plant’s pallor tells the story of its peculiar feeding methods. Rather than using pigments to gather sunlight, the roots are sheathed with fungi from whom the plant gets its food. Monotropa is quite specialized, connecting to a small number of Russula fungi species. The fungi in turn feed themselves by tapping the roots of trees, so Monotropa is indirectly feeding from other plants, using a fungus as the money-laundering intermediary. Whether the fungus gets anything in return from Monotropa is not known. The plant is usually regarded as wholly parasitic.

2015-07-13 indian pipe monotropa 009Monotropa belongs to the Ericaceae plant family, a group that includes heathers, blueberries, rhododendron, and sourwood. These species often live on nutrient-poor acid soil where symbiotic relationships with fungi help the plants to thrive in conditions that are otherwise hostile to roots. Monotropa also favors acidic areas and is often found in deep shade under conifers. It seems that Monotropa took its family heritage and changed it from mutualism to piracy. If so, this is the genus that no-one likes to discuss at the Ericaceae family reunion. Quite why the fungus would put up with its parasite is a mystery. It could be that the evolution of defensive mechanisms has not happened because the tiny Monotropa plant draws so little food compared to the supply that the fungus receives from trees. It is perhaps no coincidence that nearly all non-parasitic Ericaceae plants are shrubs and trees, and only Monotropa is a tiny sprout. The plant’s narrow range of fungal associates may also indicate that only a few fungus species can be fooled. All this has conservation implications: Chris Martine and Alison Hale have recently published a fascinating article suggesting that chemicals from invasive plants such as garlic mustard may disrupt the relationships between Monotropa and its fungi, causing population declines.

The species lives in North America, Asia, and Central America, with large geographic gaps between each population. Recent studies of DNA show that these populations have diverged from one another and have distinctive genetic signatures, suggesting that they might best be regarded as different species. How the species came to have such a distribution is unknown: the dust-like, winged seeds may have traveled by wind or the distribution may be an echo of the ancient geographic connections among these continents.

Five days after the bloom pictured above, pollinating bumblebees have done their work and the red fruit capsules are swelling. The flower’s rain-shedding, bee-welcoming droop has straightened and the fruit points directly to the sky, presumably the better to catch some favorable winds to a neighboring uncolonized fungus, or to Japan.

2015-07-18 monotropa fruit 002

Snow graphemes, scribed by plants

Fallen leaves and fruits etch the snow when caught by the wind, leaving inscrutable messages. Tree roots do the same as they carve up through asphalt. The last few weeks have provided ample opportunity to read these signs.

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These snow scribblings bring to mind David Hinton’s description of the work of the Chinese poet Summit-Gate (峰門). Summit-Gate would gather particularly beautiful autumn leaves and carefully lay them in book-scroll boxes. These boxes were her library. When snows came, she took the leaves to her poetry shelter and released them one by one, watching their wind-blown botanical calligraphy on the snow. She could read the start of every poem but, by choice, the conclusions eluded her.

There is more to her story, all told in David’s excellent book, Hunger Mountain, a meditation on landscape, mind, and literature.

So in these snowy days, we can learn from Summit-Gate and keep our eyes on the surface to see what legumes, samaras, and cast-off leaves might be saying. Ideograms are also being continually made and erased on other surfaces: beaches, dusty roadsides, perhaps even the ooze on a scummy lake. This is “tracking” of a different sort.

Orchid seeds

My ankle brushed against the dried flower stalk of a cranefly orchid and puff! a cloud of sandy dust billowed across the surrounding leaf litter. I got down on the ground for a closer look: the orchid’s fruit capsules were mature and starting to split apart.

Each capsule is roughly the size of a pinto bean. Inside are thousands of seeds. To the naked eye the massed seeds look like piles of very fine sawdust; with a squint we can make out the individual seeds. A camera lens and digital zoom lets us see a little closer.

Cranefly orchid leaf with its distinctive purple underside. The leaf appears in fall then dies in the spring.

Cranefly orchid leaf with its distinctive purple underside. The leaf appears in autumn then dies back in the spring.

Cranefly orchid capsule, split open and shedding seeds.

Cranefly orchid capsule, split open and shedding seeds.

Thousands of seeds in one capsule.

Thousands of seeds in one capsule.

A tiny puff of air is all they need to take flight.

A tiny puff of air is all they need to take flight.

These seeds owe their existence to pollination by noctuid moths. The moths suffer the indignity of carrying orchid pollen on their eyes. The cranefly flower has a slight twist and the direction of this twist determines whether the left or the right eye of the moth receives the pollen.

The wind-blown seeds’ future depends on where they land. Successful growth requires (or is greatly helped by) the presence of decomposing wood, so this orchid is one of thousands of species in these forests that depend on old logs and fallen branches.

Regular readers of Ramble will be interested to know that this orchid’s only close relatives live in east Asia. It joins many other plant species in reminding us of the ancient connections between the forest of the southeastern US and those of eastern Asia.

The abundance of orchid seeds has impressed botanists for centuries. Here is Charles Darwin calculating that one plant could in a couple of generations of unchecked seed production “clothe with one uniform green carpet the entire surface of the land throughout the globe.”

“[seeds] are produced by orchids in vast profusion. Not that such profusion is anything to boast of; for the production of an almost infinite number of seeds or eggs, is undoubtedly a sign of lowness of organisation, … a poverty of contrivance, or a want of some fitting protection against other dangers. I was curious to estimate the number of seeds produced by some few Orchids; so I took a ripe capsule of Cephalanthera grandiflora, and arranged the seeds on a long ruled line as equably as I could in a narrow hillock; and then counted the seeds in an accurately measured length of one-tenth of an inch. In this way the contents of the capsule were estimated at 6020 seeds, and very few of these were bad; the four capsules borne by the same plant would have therefore contained 24,080 seeds. Estimating in the same manner the smaller seeds of Orchis maculata, I found the number nearly the same, viz., 6200; and, as I have often seen above thirty capsules on the same plant, the total amount would be 186,300. As this Orchid is perennial, and cannot in most places be increasing in number, one seed alone of this large number yields a mature plant once in every few years.

To give an idea what the above figures really mean, I will briefly show the possible rate of increase of O. maculata: an acre of land would hold 174,240 plants, each having a space of six inches square, and this would be just sufficient for their growth; so that, making the fair allowance of 400 bad seeds in each capsule, an acre would be thickly clothed by the progeny of a single plant. At the same rate of increase, the grandchildren would cover a space slightly exceeding the island of Anglesea; and the great grand-children of a single plant would nearly (in the ratio of 47 to 50) clothe with one uniform green carpet the entire surface of the land throughout the globe. But the number of seeds produced by one of our common British orchids is as nothing compared to that of some of the exotic kinds …  What checks the unlimited multiplication of the Orchideæ throughout the world is not known.”

(p. 277-279 in Darwin, C. R. 1877. The various contrivances by which orchids are fertilised by insects. London: John Murray. 2d edition, quote from the Darwin-Online archive.)

A poppy bloom to celebrate the day

poppy

A Celandine Poppy was blooming in Shakerag Hollow this morning. I was delighted and surprised. Delighted because these are the forest’s most gorgeous flowers; surprised because the plant’s timing is unusual. Most of the plants of this species bloom in March or April, before the trees leaf out, before the summer’s heat.

Celandine poppies can self-fertilize, so the absence of other flowers will not prevent this individual from setting seed. This is a good thing for the future of wildflowers. In a changing world, the natural variation present in all populations allows species to adapt and change. So creatures who “deviate” from the norm give species new genetic pathways to the future. The unexpected sight of this flower is therefore both a sensory delight and a reminder of life’s beautiful variability and adaptability.