Polystichum acrostichoides Christmas fern

Epithet means "spreading across the surface," in reference to the sori.

description: The rhizome is branched and creeps slowly forming multiple crowns. Emerging fronds are wrapped in silky-soft silver scales. They fade to tan as they mature on the

A fertile Polystichum frond with its dark spores ripe and ready to disperse from under a lifting peltate indusia. Note too that the rachis bears a significantly thick coating of scales.

Ready-to-root bulbil on the frond tip of Polystichum setiferum X P. proliferum in the Nittritz garden. Photo by Richie Steffen, Miller Botanical Garden.

green grooved stipes that are one-third of the frond length. The blades are polished green, lanceolate, very mildly spiny, and once-pinnate with an auricle where the pinnae attach to the rachis. There are 20 to 30 pairs of pinnae. The basal pinnae are small and point slightly downwards. Fertile fronds are taller than the sterile with the sporangia confined to con-

Polystichum acrostichoides with its constricted frond tips turning brown with fertility in the Descloux garden.

Polystichum acrostichoides 'Cristatum' in the Kohout garden.

stricted pinnae on the terminal third of the frond. These will wither when the spores are shed. The sori are covered with peltate indusia. Unlike most polystichums, with sori outlining the pinnae, the sori on this species are acrostichoid, covering the entire lower surface of the fertile pinnae.

range and habitat: The Christmas fern grows in Greenland and is abundant in eastern North America from Canada down the coast and inland to the Midwest. It adapts to most soil types, likes shade, and is especially common in rocky deciduous woods and on slopes where it is welcomed for erosion control.

culture and comments: This is the flagship fern of eastern North America where, with its easy-going and evergreen nature, it is cheerful in gardens and woodlands. It is especially conspicuous in the bleak winter months, rewarding those who venture from the warmth of the hearth to garden and countryside walks. New growth arrives early in the spring in the company of wildflowers, or, in cultivation, primroses and hepaticas. While this is a staple in the east, it has not been vigorous in West Coast gardens. Are we too mild or missing summer heat? I find the best chance for success in the Pacific Northwest is to start with a good-sized mature plant. While propagation by spores is easy, this is one of the few poly-stichums that are readily increased by division. Dig the plant and carefully tease apart and cut away the separate crowns. Treat the resulting progeny to a moist site in rich compost. Most eastern growers prefer to do this surgery in early spring.

There are several explanations for the descriptive common name, Christmas fern, ranging from the shape of the pinnae supposedly resembling Santa's boot or sleigh, to the more likely, and mundane, fact that the fronds are gathered for use as decorations at Christmastime.

Polystichum acrostichoides produces stable and unstable abnormalities in pinnae shapes as well as frond division and overall plant characteristics. (See Scott 2003a, 2003b, and 2003c for an illustrated discussion of variations in plant form including pinnae and frond shapes.) 'Crispum' (curled) has wavy pinnae margins; 'Cristatum' (crested) has crested frond tips; and 'Incisum' (cut) has deeply cut pinnae edges.

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