How Did It Get There?

Ferns thrive in the Pacific Northwest. Take a walk in Bremerton’s NAD Park and you will find an astonishing variety of ferns growing in the park’s moist shady areas. Prolific as they are, I had no idea ferns can germinate without human intervention in a houseplant pot that has never been outside. Apparently they can (see photo). The answer to how this occurs may lie in the fern’s reproductive cycle.

The cactus plants in the photo were given to me by a co-worker years ago. They came in a cute decorative pot with a Mexican motif and a brief set of instructions: don’t overwater. I’m not a plant person, but even under my ownership the cacti outgrew their miniature original container. So I got a larger pot, put in some potting soil, and transferred them to their new home. That was maybe three years ago. Other than water, I haven’t added anything else to the pot.

Fast forward to the dreariest part of last winter—days on end when it was cold and rainy and spring seemed a long way off. One day I noticed a spot of green amongst the cacti. Since then the new neighbor has done well and is now recognizable as a Cactus Fern. :) Actually I think it might be a Coastal Wood Fern. So far it has adjusted to the cacti’s sporadic watering schedule and sharp spines.

Unlike flowering plants, ferns use spores rather than seeds to reproduce sexually. Fern spores, windblown, could have drifted through an open screened window in the kitchen and landed in the cacti pot. There, given a favorable combination of light, moisture, space, and temperature, the spores must have survived.

According to the Pacific Coast Fern Finder by Glenn Keator, Ph.D, and Ruth M. Heady, there’s an important step between the formation of spores and the appearance of a fern frond. Surviving spores first grow into a prothallus, a tiny heart-shaped plant that looks nothing like a fern. The prothallus produces the eggs and sperms that unite to form an embryo fern plant. Fern Finder wasn’t specific on how long this takes, but the prothallus phase could account for why my fern took so long to show itself. My best guess is that the spores arrived last summer or fall when the window was open.