I have a decided weakness for the tough little plants that somehow thrive in the cracks of old sidewalks and streets.

Cracks in the sidewalk/street occur as the concrete dries or as it settles, or as neighboring plant roots dislodge the matrix, or as the concrete responds to changes in temperature. (Such “contraction seams” are, in fact, added by design to accommodate the shrinkage caused by drying and temperature changes.) As dust, leaves, and other organic material collects in those cracks, they become plant habitat. Certainly, a variety of grasses sprout up in this constrained environment, but other flowering herbs live here, too.

On walks in downtown Coos Bay this April I’ve been admiring the geraniums that are currently blooming in some of the sidewalk cracks.

Several geraniums are common in our sidewalks and streets, including dove’s foot geranium (Geranium molle), with its nearly circular, lightly notched leaves, and red-stem filaree (Erodium cicutarium) and musk stork’s bill (Erodium moschatum). Filaree and musk stork’s bill both have leaves that are divided into many leaflets, but they differ by how deeply the leaflets are notched and how tightly the flowers are arranged.

Most of our wild geraniums have lavender-pink flowers. And most of the wild geraniums you notice have been introduced from Eurasia.

The geraniums aren’t alone in the cracks. There’s an unexpected variety of plants in this challenging environment. As the growing season progresses, different members of these intimate communities will bloom to catch your eye. A couple of different clovers, both white and red, as well as heal-all (also called self-heal), plantain, and various dandelion relatives may be living in sidewalk cracks as dwarfed individuals -- a kind of inadvertent bonsai.

Other species living in the cracks aren’t much smaller than you’d find them elsewhere, but their tolerance for the crack’s harsh conditions allow them to thrive in the absence of the weaker competition -- tiny chickweeds and small dandelions, for example.

Prostrate knotweed sends tough runners out over the ground or concrete, miniscule white flowers tucked along the rope-like stems. Several species of sand spurry can form sturdy tufts when growing in the sidewalk, although at the beach sand spurries seem more expanded and relaxed.

There are two different species of very small peas growing in our sidewalk cracks: yellow hop-clover and black medic. (Black medic is called “black” for the color of the seeds, though it has bright yellow flowers.) Both are in the clover group of the pea family, sporting heads packed with tiny pea flowers; both are quite small -- the flower heads of each are a quarter-inch across or less; both are introduced from -- you guessed it -- Eurasia.

Most of the species that can survive in sidewalk and street cracks can also live in adjacent plots but may lose out to others in those milder habitats. Too, typical sidewalk plants may go unnoticed in better habitats when they’re overrun by larger (and often less-hardy) plants.

While living in places that are dry and scorching hot in the summer and freezing in the winter, these inhabitants of our sidewalks and streets also endure extreme physical abuse: people and other animals walking and scuffing, wheels on bikes and cars crushing and tearing.

We step over them -- or on them -- and some chop them up or dig them out, burn them or poison them, but these hearty gems deserve closer, more appreciative attention.

This spring and summer look down to enjoy these beautiful evidences of life’s endurance and tenacity.

For information on how you can arrange your own exploration of our fascinating natural history, contact Marty at 541-267-4027, mgiles@wavecrestdiscoveries.com or www.facebook.com/wavecrestdiscoveries. Questions and comments about local natural history are welcome. www.wavecrestdiscoveries.com

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