Plants and Stone: Castillo de San Marcos

I wanted to follow up my previous posting on plants and geology and turn a little closer to home, though this posting features a building more than 3,000 miles from my home. In St. Augustine, Florida, the Castillo de San Marcos also functions as nursery. Started in 1672 and finished in 1695, the Castillo is the oldest fort in the United States. It is now owned by the National Park Service.

The Castillo was built by the Spanish to help defend Florida. They only had one type of stone to use, coquina quarried a half mile away on Anastasia Island. For those not familiar with coquina, I liken it to a granola bar, except that shells, broken and whole, have replaced the oats. Coquina is so soft that cannonballs fired at the fort either bounced off or sank into the stone.

A botanical survey conducted in 2003 and 2004 found 56 plant species, ranging from moss to elm, growing on the coquina walls. Cyanobacteria, nematodes, fungi, and diatoms have also established themselves on the coquina. It is quite a cozy place.

A fern garden growing in coquina

The best place to see to plants is down in the moat, on hanging gardens rich in ferns, grasses, and forbs. The gardens cover the walls every 30 feet or so, wherever water drips from scuppers that drain the courtyard roof. And the plants don’t just grow outside. In one of the courtyard rooms in the 1930s, the park service used to maintain a “fern room” almost completely covered in maidenhair fern. Now only a few ferns grow in this room.

Dark, hanging gardens of the Castillo

The walls are plant rich because the coquina is shell-rich. The heterogeneous mix of shells make a Swiss cheese-like surface, where seeds can land and get established. Water also accumulates in the cavities, further turning the coquina into a nursery.

Despite the beauty of the flowers, maintenance workers at the Castillo constantly pull out the plants by hand. They don’t want the roots to get established and destroy the fort. Cleaning the walls of plants takes about six months, though of course they can’t get it all clean and little fields of color always festoon the mighty fortress.

Plants and Stone: The Colosseum

One of my favorite little books about building stone was published in 1855. The author, an erudite English chap named Richard Deakin, turned his attention to the Colosseum, which he called “the most remarkable, the grandest, and the most imposing of all the vast ruins of Ancient Rome.” Deakin reveled in the “noble and graceful animals” who tore “each other to pieces,” and who also made meals of “numberless human beings.” But his real focus was on the plants that had taken over the great structure. In The Flora of the Colosseum, he described 420 species.

For better or worse, the modern Colosseum is a cleaned and sanitized version of its historic past. Gone are the plants that once made the building basically a big nursery. For hundreds of years, flowers, shrubs, and trees sprouted from the travertine and tuff walls. The first list appeared in 1643 and included 336 species, although this historic list does not correspond well with modern names. A study in 1815 dropped the number to 260 but then came Deakin, who appears to have combed every square foot of the Colosseum.

One of Deakin’s 420. From Smithsonian Institution Library web site.

Filled with wonderful drawings, the book is also a delight to read. Like the best interpretive writing, Deakin delves into history and science, giving each plant a story, and something for the inquisitive botanist to discover. For example, said plant lover could find cures for dysentery, gout, and rheumatism, dine on strawberries, lettuce, onions, and asparagus, and alleviate the effects of “too great potations” of wine. If you are interested in testing Deakin’s hangover cure, all you have to do is find some Hedera helix, better known as English ivy.

Alas, archaeologists in the 1870s recognized how damaging plants were to the structure and stripped the green mantle. Diversity also decreased with the loss of grazing animals and their contributions to soil fertility. Not all plants have fared poorly in modern times: the most recent floristic study, conducted in 2002, reported that alien species, particularly those associated with humans, have flourished. The 2002 study described 242 species, and total diversity for all studies is 684 species.

Although I understand why workers in Rome remove the plants, I wish they didn’t have to. At least the plants grow fast enough that I can still see this wonderful link between geology and botany.