Japan is home to a number of Polystichum species, but two dominate in southern Japan’s forests, P. polyblepharum and P. tripteron. The former is common at low elevations here in Fukuoka, belying its preference for the warmer parts of Asia, while the latter is a straggler to Japan’s southern forests, more suited to the cold temperate woodlands of northern Asia.
Polystichum polyblepharum is an evergreen fern with a short creeping rhizome that sometimes forms a small trunk. The frond is twice pinnate, growing up to 100 cm long. They grow in a rosette forming a near perfect circle. The pinnules are boot shaped and have slightly toothed margins with a pointed tip. The round sori are in rows along the costa. The thick, fleshy stipe is covered in large cinnamon brown scales and accounts for about one quarter the length of the frond. The unfurling croziers hang down at their tips, giving them a drooping, tassel-like shape typical of this genus. While this fern can create offsets from the rhizome, the plant is more commonly seen growing as a single rosette of fronds.
In Japan it is widespread from Honshu and southward. It is also found in South Korea, and the warmer parts of China. In the Fukuoka area it is found in moist woodlands from near sea-level to over a 1000 meters. This is one of the most commonly seen woodland ferns in Fukuoka and indeed much of the warmer parts of Japan. One of its most distinguishing characteristics are the large cinnamon colored scales that cover the stipe and rachis. They are particularly noticeable when the croziers just emerge.
The half grown fronds hang down as they elongate, giving this fern its English common name, the tassel fern. The overall visual impression of this species is very pleasant since it forms perfectly circular rosettes of fronds up to 2 meters across in vigorous specimens, but more commonly half that size.
The upper surface of the pinnae are a beautiful, glossy green that gives off a bluish sheen. A multitude of white hairy scales cover the lower pinnae surfaces and give the plant its Latin name, polyblepharum, meaning “many eyelashes”, however they are not easily seen by the naked eye.
In truth there are a number of near look alike species from this genus, and to tell them apart you have to closely examine their scales and pinnae. If that weren’t bad enough, members of this genus hybridize readily, thus compounding identification. I have decided to avoid all that and simply lump them all under this species. A lazy approach, but one has to be careful how time is spent in life!
Nearly as common, but more confined to higher elevations on Kyushu is P. tripteron. It too is evergreen with a short creeping rhizome, however it is a much smaller species. The fronds are unique in that they have three pinnae; a basal pair and a much longer apical pinna (perhaps 4 times longer than the basal pair), thus forming a cross or trident shape. Each pinna is divided once again and the total frond length is between 25-60 cm long. The fronds grow in whorl such that they sometimes form a perfect circle with the smaller basal pinnae pair making an odd inner circular pattern. The pinnules are sickle or boot shaped and have toothed margins. The round sori are in long rows along the costa. The stipe is covered in dark brown scales and accounts for about one third the length of the frond. The unfurling croziers hang down at their tips, in a tassel-like manner (certainly one of the easiest ways to identify a Polystichum). This is a clumping fern and often creates offsets from the rhizome.
P. tripteron is widespread on all the mainland Japanese islands, and also eastern Siberia, northeast China, and Korea. Locally it is a fern of moist valleys, especially near streams and on seepage slopes, preferring the cooler mid to high elevations, 500-1000 meters.
This is a northern fern more typical of a Manchurian forest that has straggled south all the way to the mountains of Kyushu. It is found throughout the higher elevations here, but not any further south. Most often you’ll see it growing very close to streams, almost in them sometimes. This perhaps is due to the evaporative cooling that mountain streams afford. On a hot August day if you get in the vicinity of a one you can feel the temperature drop 5 C or perhaps more. In one valley I have found ones growing nearly epiphytically on moss covered trees. This plant is one of Kyushu’s more unique looking ferns. It grows its trident shaped fronds in a perfect little circle and even has a short trunk-like stem. The pinnae are typical of this genus in that they are sickle shaped.
The Latin name, Polystichum, is from the Greek words poly meaning much or many and stichus meang row or line. This is in reference to the sori being in multiple rows. Polyblepharum in turn is from the Greek words poly meaning much or many and blephar meaning eyelash – definitely a reference to the multitude of whitish hairs found all over the bottom sides of the fronds. Tripternon is the combination of the Latin word tri meaning three and, the Greek word pteron meaning wing or feather – again, the reference is straightforward: the trident shaped fronds.
The Japanese name for P. tripteron is juumonjishida, meaning “cross fern” from the words juumonji (“cross” or “cruciform”) and shida (“fern”), another reference to the cross shaped fronds. P. polyblepharum is called inode, meaning “boar hand” from the words inoshishi (“wild boar”) and te (“hand”) – for the life of me, I cannot figure that one out! Perhaps the whorl of emerging scale covered croziers reminded someone of a wild boar’s hoof?
While these ferns have different temperature tolerances, both seem easy garden subjects requiring no special care, at least my house. They happy grow in the native soil (a woodsy loam) with no amendments whatsoever in bright to moderate shade. Being ferns of moist woodlands, they don’t like drying out. Both are evergreen in Fukuoka, however, I would imagine in colder climates they could lose their fronds in winter.
Since it is more suited to warmer climates, I’d guess that P. polyblepharum should be fully hardy to USDA cold hardiness zone 7 and perhaps lower with mulch. P. tripteron is found in Siberia and Manchuria, and so should be hardy at least to zone 5.
While both seem tolerant of hot conditions in summer, they very likely need a “real” winter, that is, they are true temperate species. The mountains and foothills of southern Appalachia would be perfect for both no doubt. Unassuming, but lovely, and easy to cultivate – not a bad combination, and both of these tassel ferns fit the bill.