A holly fern can refer to one of two varieties of fern. Cyrtomium falcatum, or Japanese holly fern, is native to parts of eastern Asia. Polystichum lonchitis, commonly referred to as northern holly fern, on the other hand, is more widely distributed and can be found growing in most of the northern hemisphere, including North America and Greenland. Both ferns earned the nickname of holly fern because their leaflets bear a strong resemblance to holly leaves.
The fronds of the Japanese holly fern are often between 18 and 20 inches (45 to 61 centimeters) high, but have been known to be as high as 36 inches (91.4 centimeters). Each frond can be up to 7 inches (17.8 centimeters) wide and made up of 4 to 10 pairs of large pinnate leaflets. These leaflets are typically quite leathery, glossy, and dark green in color, with serrated, toothy edges that come together in a sharp point.
Japanese holly ferns, as the name suggests, were originally native to Japan. In other parts of the world, these are a popular choice for houseplants. At some point, they escaped into the wild, and can now be found growing in moist, shady wilderness areas in many parts of Europe and North America.
Northern holly ferns are roughly the same height as the Japanese variety. The fronds of the northern variety, however, are narrower, measuring roughly 2.5 inches (6 centimeters) wide. The base of each frond is narrow, becomes wider somewhere above the middle, and ends in an arching tip.
Leaflets of the northern holly fern are also a dark glossy green with serrated edges and a pointed tip. They are much smaller in size though, and because of this, there are more on each frond. Each frond is made up of about 25 to 35 pairs of pinnate leaflets, which rarely get larger 1.5 inches (4 centimeters) long.
Both varieties of holly fern have spores on the underside of each frond, which enable the plants to reproduce. When young, these spores are usually light green in color. As the spores mature, they become much darker, and may even look black.
Japanese and northern holly ferns both need a moist environment to survive. If they are grown indoors as houseplants, the soil must not be allowed to dry out during watering. Inside they will thrive in full sun, but if they are planted outdoors, they prefer shady or partial shady areas.