Polystichum acrostichoides

For a plant this common, the Christmas fern carries an oddly specific origin for its name. It was christened, the story goes, by one John Robinson, a botany professor at the Peabody Academy in Salem, Massachusetts, sometime in the late 1800s, and set down for posterity in a 1923 volume with the irreproachable title The Fern-Lover's Companion. Robinson's reasoning was seasonal. When the other ferns of the eastern woods go brown and crisp at the first hard frost, Polystichum acrostichoides holds its green straight through December, which made it the fern people cut for wreaths and mantels at Christmas. There is a second theory, quieter and harder to settle, that the name comes from the leaflets themselves: look closely and each pinna carries a small lobe at its base, an ear or a thumb, that gives it the outline of a Christmas stocking. Both camps are probably right.

The Latin, for once, is plain description rather than flourish. Polystichum means many rows, for the ranks of spore cases lined up beneath the fertile fronds; acrostichoides means it resembles Acrostichum, a leather fern whose spores cover the leaf almost completely. The botanists named it twice for the same modest feature and left the poetry to the common name. They grow in a tidy fountaining clump, eighteen inches to two and a half feet, the fronds leathery and dark and lance-shaped, rising from a central crown rather than running off across the bed. In spring the new growth uncurls as silvery, scaly fiddleheads, the most ornamental moment in an otherwise composed year. The fronds that come up first are usually the fertile ones, held stiffly upright with their upper third contracted and browned beneath with sori. The sterile fronds follow, lower and looser, and those are the ones that stay green.

What they do in winter is the whole reason for the name, and one of the more endearing habits in the genus. As the cold sets in, the evergreen fronds give up their upright posture and lie flat to the ground, pressed low under the leaf litter and the snow. It reads as collapse and is in fact strategy: flattened against the earth, the fronds ride out a freeze that would shred them standing, and rise again when the ground warms. Give them organically rich, acidic, well-drained soil in part to full shade, hardy across a remarkable run from Nova Scotia to the Florida panhandle, zones 3 through 9. They want moisture while establishing and turn surprisingly drought-tolerant once settled, holding their ground in the dry rooty shade beneath big trees where most things sulk. The one thing they will not forgive is wet feet in winter, which rots the crown. Deer and rabbits walk past them. Massed on a shaded slope, they knit the soil and hold it.

A fern that decked the halls before anyone thought to plant it on purpose: green at the solstice, flat under the snow, and standing again before you have quite registered that winter is over. The quiet backbone of the Eastern woods, and one of the few green things left when the rest of the garden has gone to sticks.