Away Dog! Apocynaceae, the Dogbane family

Near my house, next to the road the ground is sandy with a scattering of pebbles in the mix.  Like much of Vermont what is not bedrock is ground up glacial debris deposited when the vast continental glaciers melted away.  The ground is sandier than most places at my house because I am perched on the southern slope of a small rock outcrop, a place where the downward pressure of the glacier was lighter, water flowed under the ice, and fine sediment was deposited.

In that sandy ground there are wild strawberries, mosses, dandelions, fleabane, hay scented ferns, a few coneflowers, some potentillas, Allegheny blackberry, a little bracken fern, and a small stand of dogbane (Apocynum cannabinum) with delicate pink flowers.

Hemp Dogbane (Apocynum cannabinum)

Before moving to Vermont my only experience with this plant was via books.  I always wondered why it was called Dogbane.  Was it like negative catnip for dogs?  Or was it simply toxic to dogs?  Apparently it is a toxin, and not just to dogs.  Ingestion of any portion can induce cardiac arrest and both the family and genus name literally translate to, “Away Dog!”  Apocynum cannabinum has, thick, milky sap, much like a milkweed, indeed Milkweeds (Asclepiadoideae) are now considered to be a subfamily of the Dogbanes (Apocynaceae).  Other members of the Dogbane family include two of my least favorite plants, Oleander and Vinca, both from the Mediterranean and common in California where they were introduced as ornamentals.  Oleander can be seen in any urban environment in Southern California, most often as a highway divider plant.  The sap is extremely toxic, raising painful rashes, and the smoke can be lethal if inhaled.  Vinca, more commonly known as periwinkle, is  common in Northern California where it invades riparian areas, covering both ground and small trees in a dense, vining mat of glossy green leaves studded with pretty blue flowers.  It is nearly impossibly to eradicate once in place.

In the past some Apocynaceae species were used to make a poor quality rubber, others for toxin to apply to arrows.  Some species produce edible fruit and others edible flowers.  We extract heart drugs from a few of them as well.

The dogbane in my yard, Apocynum cannabinum, is a traditional North American source for extremely strong fiber, hence the “cannabinum ” species name, referring to the hemp-like characteristic of the plant.  Common names run from simply Dogbane, to Indian Hemp, Wild Cotton, and Hemp Dogbane.  The fibers are stripped from the stalk in late fall and can be twisted into a fine, strong cord.  Cords made from dogbane were prized for their great strength and used for sewing, fishing lines, and other work requiring fine cordage.

The Hemp Dogbane ranges from calf high to chest high.  The ones in my yard top out at waist high.  The have an odd branching structure, perhaps best described as irregular opposite.  The main stalk continually divides in a binary fashion, with one side acting as a dominate leader, this pattern is often repeated on the side branches, but in some cases buds on both side of the stem will form side branches instead.  The result is a roughly Y shaped plant that rapidly spreads as it grows.

Apocynum cannabinum whole plant.

The leaves are opposite and the undersides are covered with a fine pubescence.  I expect that the hairy leaves are an adaptation to help cope with moisture stress.  Plants often evolve this trait to create a boundary layer of trapped, still air that aids in preventing moisture from being blown away.  The upper leaf surfaces have a matte waxy texture, a little like nasturtium leaves.  Water beads and runs off of them rapidly.

Apocynum cannabinum leaf hairs

The seeds are held in long, horn-like pods.  This time of year few of the seed pods have developed, but a couple of plants are a little further along in the cycle than others.

Apocynum cannabinum seed pods, not fully developed

Few of the leaves have any insect damage, but the flowers are popular with a number of insect species.  I’ve seen ants, flies, bees, and moths going to them.  Hidden amongst the flowers are predators as well.  The Goldenrod Crab Spider (Misumena vatia) seems fond of my dogbane.

Goldenrod Crab Spider (Misumena vatia) playing parlor games with a fly

Goldenrod Crab Spiders are so called because they often hide amongst the bright yellow flowers of goldenrod, a common meadow plant in New England.  The spiders change color from white to yellow and back again based on input from their eyes.  The yellow color seeps up to stain their carapace, providing camouflage.  When they move to a pale flower the production of this pigment stops and the spiders slowly turn white once more.  Experiments show that the spider will not change color if it cannot see what color plant it is on.

These are not web building spiders, they are ambush hunters, grabbing unsuspecting prey in their wide arms.

The smell of the flowers is odd and difficult to describe, incorporating many scents including a dusty sweetness and a faint rankness like dried meat on the edge of going bad, but they are pretty.

Glaciers and Camel’s Hump

Glaciers, geology, and meteor impact craters have always fascinated me.

Right now I live in New England, a landscape that was recently, geologically speaking, glaciated.  It has been about 12,000 years since the large glaciers here melted, leaving nothing behind but water, exposed bedrock, and a rubble of loose stones of various size and mud made from pulverized stone.  Plants raced for the freed nutrients and the forest wandered north with them.

Now Vermont is thickly forested up to all but the highest peaks.  Despite this signs of that past glaciation are everywhere, from large landscape features to the fine scale distribution of plants across that landscape.

One of the most prominent glacial features is the mountain Camel’s Hump, which, though not tall, can appear to loom over Burlington despite being 20 miles away.

I think it’s the implacable power of a glacier that awes me.  Large glaciers are otherworldly in a way that is difficult to convey.  The best description I have heard was in southeast Alaska where the large ice-fields are said to be the home of  the dead.  I spent two months working with a small group of people on the ice and it was easy to see why people said that.

Camel’s Hump, the mountain in the distance is a little over 4000 feet tall.  That’s a bit less than a mile.  At the height of the last glaciation the ice was more than twice that thick, burying Camel’s Hump so completely that you would only be able to tell it was there by looking via radar, sonar, or gravity scans.  If you were there, you would be standing more than a mile above the mountain top looking at a flat white plain stretching past the horizon in all directions.

That vast depth of ice weighed an enormous amount and moved under its own weight, slowly flowing across the landscape.  Glaciers are continually melting and the streams refreeze elsewhere.  Some of this water finds its way to the bottom of the glacier and refreezes in cracks in the underlying bedrock the glacier has just scoured clean.

Water expands when it freezes and fragments of the bedrock were broken free and held, frozen into the bottom of the glacier.  These entrained rocks scour the bedrock, like a file on metal, wearing it way, grinding it up, and tearing it loose.  The shapes a glacier carves the land into are extremely characteristic and have their own specific names; col, cirque, esker, moraine, drumlin, chatter mark, arête, roche moutonnée, and many more.

The glaciers that covered the New England landscape were large and the features they left are correspondingly large.

Camel’s Hump is a textbook example of a large roche moutonnée.  Roche moutonnée are low, rounded humps of bedrock rock that are ground into their shape by the action of a glacier.  I assume roche moutonnée owe their name, “sheep rocks”, to French and Swiss sheep herders who would have spent a lot of time looking at these low, rounded rocks while thinking about sheep.

The shape of a roche moutonnée shows the direction of glacier flow, and from Camel’s Hump you can see that the ice flowed from the north to the south, from right to left in the photo above.

The northern surface has been ground to a shallow angle, while the south side is steep and jagged, where the glacier ripped cathedral sized chunks of rock loose.

There is a clear vegetation line on the mountain, hardwoods lower down, evergreens above.  In Vermont the vegetation line is due primarily to temperature, moisture, and elevation.  In areas more recently deprived of their glaciers the bands of vegetation climbing the slopes provide an accurate means of dating how long it has been since the glacier left.

Nothing in nature is random, the glaciers don’t just carve their way willy-nilly across the land, their actions are directed by the bedrock they are so eagerly tearing asunder.  Camel’s Hump was a mountain before the glaciers came, and the glacier could only modify what was there, not make something completely new.

Seen from the south side, where the freeze/thaw and continual motion of the glacier have exposed the mountain’s heart you can see the folded, pastry dough like layers of rock that make up Camel’s Hump and the Green Mountains.

The tree covered slope beneath the cliff is a a boulder field dropped in place as the glaciers melted, now colonized by spruce and moss.

Ice to Water – Rock to Liquid

One of the most impressive, magical, and least appreciated spring changes is taking place right now in Vermont and through much of the northern portion of the globe.  In damp, shady, north facing areas ice is melting, becoming water.

This is a remarkable transition, a hexagonal mineral, ice, is, all by itself, changing its phase state, becoming an amorphous liquid.  In essence, boulders, cliff faces, and sand banks are melting and flowing away.  It is as though the rocky hills and mountains of the world slithered into the valleys and flowed to the sea every year.

The big solid blocks of ice form in the same manner as igneous rocks, water taking on the role of cooling magma.  A frozen waterfall is akin to a solidified flow of low gas content lava in Hawaii or Iceland.

Melting ice soaks into the ground carrying the sun’s heat with it, defrosting the frozen ground, waking up trees, plants, and animals, recharging groundwater resources, making streams flow, and redistributing nutrients.

The ice fall to the right was formed last winter from ground water seepage.  The base of the icefall spreads, molasses like, over a steep slope of boulders covered in decaying leaves, richly organic soil, and moss.  The melt water sinks directly into the ground, speeding the decomposition of leaves and woody debris, trickles down to the shallow bedrock, flows along this impermeable surface, and reemerges downslope in the company of ostrich ferns, blue cohosh, maiden hair ferns, and red cup fungus.

Right now, most of the plants are still waking up, small shoots and sprouts just beginning to emerge from the thawing ground.  Some plants have a jump on the process.  In relatively undisturbed areas of the New England forest near steep streams and seeps a forest dwelling sedge has been waiting all winter under the snow.

Carex plantagineaSedges are more often found in the open, in wet fields, swamps, marshes, and the like, but plantain leaved sedge (Carex plantaginea) is a true forest dweller.  It is an evergreen perennial with broad, thin leaves to best collect the dim sunlight that penetrates to the forest floor.  It lies flat under the snow, perhaps beginning to photosynthesize even before the snow fully melts, relying on the light that filters through the fluffy layer of sand-like ice that is snow.

Undisturbed stream banks, are festooned with this early wakening plant.  Sometimes it looks as though someone scattered dozens of limp green pompoms over the ground near the streams.

These small streams are particularly active this time of year.  The tumble down steep slopes, splashing from cobble to boulder, their flow more a series of miniature waterfalls than anything else.  The constant churning and splashing oxygenates the cool water, this oxygen allowing insects and amphibians to live in the steep streams and fish to live in the deeper, more slow moving rivers.

On a sunny day there is little more enjoyable than to sit in the forest listening to the sound of swift moving water and let your eyes and mind wander the landscape.