At the edge of Nicholson Park, there is a mound, almost a tiny hill, of soil and trash left over from clearing a parking lot, long ago. Every summer, it is covered by a thicket of mixed blackberry canes and other weeds; I always stop as we pass, to look at caterpillars and ladybugs. Yesterday's honeybee was on a clump of dandelions along the edge. This year, someone has cut down the blackberries. In their stead, a forest of Japanese knotweed is springing up; not a good development.
But before the knotweed gets its full size, horsetails are having a go at colonizing the newly-emptied ground.
|Horsetail, dead leaves, dandelion, ladybug. And a bit of blackberry, coming back. It always does.|
At this time of year, horsetails take two forms: a green stalk with a series of whorled branches, which will persist until fall, and a short-lived bare stalk topped with a spore-bearing cone. This will die back as soon as the spores are released.
|Fertile stem and strobilus on the left, green steriles on the right.|
The horsetails are survivors from an ancient earth, smaller than their ancestors, but still maintaining their unique way of life. They are non-flowering, reproducing by spores like mosses, but not related to them, or to any other plants: they are the only remaining genus in their biological family.
The name, horsetail, or Equisetum, (from Latin equus and seta -"horse bristle") describes them well; the branched species look sort of like a horse's tail. The silicates that coat the stems also give them the texture of a horse's tail hairs: stiff and rough, sandpapery. They have been used as scouring material. When you've burnt your meal, cooking over a campfire, look for horsetails. A couple of handfuls will clean your frypan up nicely.
As for the way they're put together, anything we take for granted in "normal" plants is the opposite in horsetails. Look at the photos of the stem and branches. Yes, the green, needle-like things arranged in whorls at the joints of the stem are branches. The leaves are not on the branches, but form tight, papery sheaths around the stems, like a decorative frill, whitish with brown tips. They are not equipped to perform photosynthesis, like the leaves of most plants do. The sterile stems and branches contain chlorophyll and do the work of transforming sunlight into sugars instead. The fertile stems of the field horsetails are non-photosynthetic; these fertile stems consume food, but produce only spores.
|Detail, stems, branches and leaves.|
|Sporulating head of giant horsetail, Mud Bay.|
There are two main species in this area; the common or field horsetail, and the giant. Both are similar, but easily distinguished by size alone. The field horsetail grows to about two feet tall, with fertile stems being half that. The giant's fertile stems are up to 2 feet tall, with the sterile stem growing even up to 10 feet.
|Spore-bearing heads of giant horsetail, growing through ditch weeds.|
And why I won't allow even one to sprout in my yard and garden: not only are the spores good at what they do, starting new plants, but the roots go down forever. (Or up to 20 feet through hard-packed clay; whichever comes first.) When the plants die down in winter, they are not gone. They're biding their time, spreading themselves about, getting ready to shoot up those fertile heads before the weather lures us out into the gardens again. Digging them out doesn't hurt them; a bit of rhizome left in the soil is enough for regeneration.
Ripping out most of the plants won't kill them, either. It's all or none, because the colonies are clones; each one is part of the whole.
|Field horsetail, taking over a gravel pile in our vacant lot.|
They grow in wet soil, in dry soil, in clay, in gravel. And in good garden loam. They grow even through a layer of heavy rock. For example:
|Fertile spore cones of giant horsetail, pushing through the rock rip-rap beside the railroad track at Kwomais Point.|
There are a couple of great photos of fertile cones, here, on Dave Ingram's blog.