Basal Rosettes: Life in the Flat Lane

Amsterdam High School. I spend quite a lot of time in this parking lot, waiting waiting waiting for soccer practice to be over. So today I looked around to see who else is hanging around the blacktop.

This little opportunist is a species of thistle, I believe—not sure which one. The leaves are spread out flat, hugging the pavement—a very successful growth pattern, called a basal rosette. This growth pattern is common to a lot of the members of the Compositae (also called the Asteraceae), a huge group of plants that includes thistles, asters, daisies, knapweeds and dandelions.

In a basal rosette, the leaves are arranged in a circle, all at about the same height, like the spokes of a wheel. This flat structure is a superb adaptation for survival. It shades out the competition. The outspread leaves grab drops of rain, which run down the center of the leaves and are funnelled straight to the roots. Each leaf is placed to absorb the maximum amount of sunlight.

The flat growth pattern means the plant doesn’t have to put large amounts of energy into strong, tall stems. The leaves lie flat, supported by the ground, so you can literally walk all over the plant and not harm it. Mowers and weedwhackers pass by harmlessly overhead.

Some plants are biennials, which means they have a two-year lifespan. The whole first summer of the plant’s life, it’s a lowly basal rosette, attracting no attention but making lots of food which is stored in the root. The plant overwinters, in some cases staying green even underneath the snow, and then in its second spring it gets a major head start on the competition, using last summer’s energy to thrust up a long stalk and produce flowers and lots of seeds.

Some but not all thistles are biennials. If this is one, this little guy might not do so well next year, when it’s time to send up a tall stem. But for right now, being flat is working well.