For years, I ignorantly assumed that ferns, because they aren’t flowering plants, can’t hybridize. They can, of course—they just do it in a very tricky way. When a fern spore germinates, it grows into a small, thin, heart-shaped structure called a prothallus. On the underside of the prothallus, sperm travel through a film of water to fertilize an egg, which then develops into a sporophyte, or what we recognize as a fern. When the prothalli of two related species grow right next to each other, the sperm of one can cross over to the prothallus of the other, and a hybrid sporophyte may result.
This is probably more than you wanted to know about fern sex, but the process has yielded some first-rate plants. One of the most exciting is the aptly named Athyrium ‘Ghost’, a medium to large upright fern whose fronds are the delicate gray green of celadon-glazed porcelain. It was discovered two or three decades ago by the late fern enthusiast Nancy Swell among a batch of sporelings she was raising from a giant form of the Japanese painted fern (A. niponicum var. pictum). In fact, five percent of the sporelings showed the pale ‘Ghost’ coloration. She sent one of these to John Mickel, curator of ferns for the New York Botanical Garden, and, gardeners being inveterate sharers, it slowly found its way into the nursery trade. Only in the last few years, however, has it become widely available. The putative parentage of ‘Ghost’ is A. niponicum var. pictum crossed with A. filix-femina, but Nancy suspected it may be a back-cross of the Japanese painted fern, even though ‘Ghost’ is sterile, which would seem to confirm its hybrid status.
Whatever its origin, ‘Ghost’ deserves a rousing welcome, not only for its own subtle beauty, but also because it is one of those invaluable plants capable of brightening the gloom in shady gardens. I have a patch of it in a bed devoted to blue and gold foliage, where it provides just the right textural contrast to the small Hosta ‘Bluejay’ and Carex ‘Burton’s Blue’.
Like other members of the genus Athyrium, ‘Ghost’ does best in moist but well-drained, humus-rich soil beneath the dappled shade of deciduous trees. With their thin, delicate fronds, athyriums are especially susceptible to drought, and will need supplemental water during dry spells. An annual application of compost is all that’s required in the way of feeding.
“Crossover appeal” is a term usually applied to certain pop songs, but I think it’s apt in this case as well. If you’re already a fern fanatic, it’s a pretty safe bet that ‘Ghost’ will make you feel faint and tingly; if you’re simply a generalist gardener who likes a good plant, then ‘Ghost’ could well be beginning of a new—dare I say haunting?—passion.
A version of this article first appeared in Horticulture magazine, vol. 100, no. 4 (July/August 2003).