Carderock, May 2


The morning of May 2 I set out for a quick survey of the greater Carderock area, with the goal of shooting some long-tube valerian, a highly state rare/endangered species that grows in several different locations in the Potomac gorge.


Along the way, on the towpath between the Billy Goat C and Billy Goat B trailheads, I noticed that a lot of trees along the stone retaining wall were missing.

What the heck? Wondering why, I decided to call the park and inquire when I got home.

I didn’t need to. A few hours later, on the way back, I saw a ranger taking photos, so I asked him about it. In summary, the retaining wall is historic, and it’s been in danger of being damaged by the trees, some of them were quite large. If one had gone down in a storm, the root mass lifting out of the ground could have caused a breach in the wall. Not only would that severely damage the canal and make that part of the towpath unusable, but an 8′ diameter sewer main, part of the Potomac Interceptor sanitary system, runs along there. It, too, would be severely damaged by a breach in the wall.


The flags marked a line 20 feet from the base of the wall; all the activity is being kept within that zone. They will be installing some monitoring equipment in order to track changes to the wall in coming years.

My main concern, of course, was damage to plant communities. Good news: the park always has an expert come in for a plant survey before they do any work.


Annoyingly the narrow strip of land between the towpath and the wall gets moved every few weeks, but if you go now, you’ll see some lyre-leaf sage blooming in there. The plants are quite short, but year after year they survive the mowers.


The spring ephemerals are almost entirely gone, just a few spring beauties left. Observed blooming on May 2:


  • wild blue phlox (waning)
  • star chickweed
  • Virginia waterleaf (just starting)
  • Coville’s phacelia (past its peak)
  • long-tube valerian
  • clustered snakeroot (just starting)
  • golden Alexanders (S3 – rare to uncommon)
  • rattlesnake weed
  • hairy beardtongue
  • moss phlox (waning)
  • field chickweed
  • wild geranium
  • rue anemone
  • lyre-leaved sage
  • Rubus species (probably a dewberry)
  • azure bluets
  • dwarf cinquefoil
  • plantian-leaved pussytoes (waning)
  • bastard toadflax
  • fringetree
  • deerberry
  • alumroot
  • violet wood sorrel
  • wild pink (a day or two away from being done)
  • spring forget-me-not
  • Virginia spiderwort
  • common wood sorrel
  • Philadelphia fleabane

Slope Fen, Cape Breton Highlands


Looks like a grassland at the edge of the boreal forest, doesn’t it?  Actually, it’s a slope fen; there’s water flowing very, very slowly under there.  You can’t walk across it, but there is a boardwalk around it.  There are a few open pools of water within.


So you might be wondering, as I did, what distinguishes a fen from a bog, or from any other type of wetland?  And what exactly is a wetland?

According to Lewis Cowardin of the US Fish and Wildlife Service, “wetlands are lands where saturation with water is the dominant factor determining the nature of soil development and the types of plant and animal communities living in the soil and on its surface (December 1979).”

There are four main types of wetlands: marshes, swamps, bogs, and fens.

Marshes are wetlands dominated by herbaceous vegetation.  Most of the water in marshes comes from the surface, but in many cases groundwater is also a source.

Swamps are wetlands dominated by woody vegetation.  There are a few swamps on the Maryland side of the Potomac gorge.  Long-tube valerian, winged monkey flower, and lizard’s tail are some of the wildflowers I’ve found there.

Bogs are wetlands formed by the growth of sphagnum moss either over a pond, filling it in, or over land, preventing water from evaporating.  Either process results in a wetland characterized by very acidic water and a low amount of nutrients.  Not many plants are well adapted to these conditions.  Regardless, the bottom of a bog is generally impermeable, so most of a bog’s water comes from precipitation.

A fen is basically a bog that receives some groundwater; as a result, fens have more nutrients and less acidic water.  They support a broader range of plants than bogs do.

Bogs and fens are found mostly in the higher latitudes of the northern hemisphere, and in some alpine areas in the middle latitudes.  There are no bogs or fens in the Potomac gorge.


A slope fen is exactly what you’d think it is: a fen situated on  gently sloping land. Sadly I did not learn the names of most of the plants I found here, though I believe the area is dominated by rushes, not grasses.  (Hmm, now I have an idea for another blog post.) 20140915-DSC_0200

If you click on the first picture and zoom in, you’ll see some goldenrods and a northern pitcher plant.

In case you were wondering, the sevenangle pipewort featured on November 26 was found in the shallows of a very large pond, not in this slope fen.