The lower mountain forests of Kyushu boast some of the largest fern species. In this discussion we’ll look at the four largest types of fern in the area around Fukuoka Prefecture. These include two species of Pteris, as well as two species of Woodwardia.
Pteris excelsa is a tall evergreen fern with two frond types that are morphologically distinct: the sterile fronds (the trophophylls) and the fertile fronds (the sporophylls). The sterile fronds are twice pinnate with the end of each pinna ending in a spear-like pinnule that occur in an irregular pattern. They are up to 150 cm long and around 60 cm wide. These tend to grow horizontal to the ground or arch downwards. The fertile fronds are much taller and stand nearly erect, sometimes as high as 240 cm long. They lack the spear-like terminal pinnules of the sterile frond, and each pinnule tends to be much more narrow as well.
The emerging crosiers and stipe are covered in a light white pubescence, but this is lost once the frond is mature. The sori are born on the outer margins of the pinnules, covered by the folding in of the margins. This fern is most commonly found in lose small groups, often growing on wet seepy slopes and relatively bright forests, but occasionally next to stream sides. It occurs at fairly low elevations, 50-600 meters.
This is a big fern, in fact taller than Woodwardia orientalis, the most massive and impressive fern in Fukuoka. The growing crosier is a sight to behold with each pinna all curled up, ready to unfurl. Furthermore it is covered in a light white pubescence which is stunning to see in person. This is definitely one of Fukuoka’s more spectacular ferns.
A fern that looks more like a true bracken, Pteris wallichiana, is large, evergreen, and clumping. Both sterile and fertile fronds have nearly the identical look and dimensions. The stipe stands almost vertical, is completely smooth and scale less, and accounts for over 2/3 of the frond length growing up to 130 cm high. At the highest point of the stipe the frond branches out in three directions. The outer branches divide once more to form two forked branches. The center branch grows the longest and doesn’t divide again. The result is a palmate blade forming a lopsided circle ranging from 60-80 cm wide.
The fronds are twice pinnate and the pinnules are slightly lobed. As in the former species, sori are born on the margins of the pinnules and are protected by false indusia that are in fact the pinnule margins folding in and over the sori. Plants can form large clumps in time. This species seems to like moist to wet slopes in bright woods, tree plantations, and also along streams. It is found at low to mid elevations, 300-500 meters.
Here’s another one of Fukuoka’s oversized ferns. The frond can measure nearly 2 meters in length, stand up to 1.3 meters high, and be nearly a meter wide. Now that’s a nice big fern! The bulk of its range lies in southeast Asia in decidedly subtropical to tropical regions, although it can be found up to the central coast of Honshu. While it appears to be evergreen here, I’ve heard that it is deciduous in winter further north.
Here’s a video showing not only Pteris excelsa and P. wallichiana, but also four other Pteris species common to northern Kyushu: P. multifida, P. cretica, P. nipponica, and P. dispar.
Woodwardia japonica is another large evergreen fern with long, broad fronds up to 150 cm long and 40 cm wide at the broadest point of the blade. The blade is once pinnate, and each pinna is deeply lobbed, nearly forming a second set of pinnules. The emerging croziers and stipe are covered in reddish-brown scales, a feature the stipe retains after fully grown. The sori are linear and arranged in parallel lines on both sides of the costule of each lobe. This arrangement is very tight, thus belying the chain-like pattern common to this genus.
While this plant grows from a single crown, it occurs in loose colonies. It is found in moist woods in deep to bright shade, and prefers well drained slopes at low altitudes, 50-200m. Japan is the northernmost limit of this species which is more broadly distributed throughout southeast Asia. Visually it is a magnificent fern, and worthy of a place in the garden.
The so called oriental chain fern, Woodwardia orientalis, is the largest fern in the Fukuoka area. The rhizome is massive and the fronds are equally so, up to 200 cm long and 60 cm wide, making it a tree fern wannabe. The fronds are twice pinnate and each pinnule is unlobed. The pinnule surface is marked with elongated bumps created by the deeply set sori on the underside of the pinnules. Pinnae also can produce asexual buds that can form into many young plants (hence another common name, the mother fern). These buds grow into little bulbs that in turn produce a tiny triangular frond. The stipes are covered in large red-brown scales and are thick and fleshy.
Plants usually occur in small colonies, but occasionally can form massive ones with hundreds of plants covering a rock face. It has a preference for moist hillsides on almost vertical slopes, particularly next to cuts made for roads. It can be found in low to mid elevations in Kyushu, 50-400 meters.
This is indeed the grand daddy of all ferns locally with fronds up to two meters in length. When growing on a vertical slope the huge, broad fronds arch gracefully downward giving a very tropical look. The emerging and elongating croziers are no less spectacular. Each pinna unfurls in an elegant downward arch and is covered in reddish brown scales. Furthermore, the recently grown frond often has a nice light bronze color showing this species’ alliance to the genus Blechnum. This color however quickly fades to a rich bright green. Truly a remarkable fern.
Of the four ferns mentioned, I’ve grown all but one, P. excelsa. The main limiting factor for these is cold hardiness, especially W. japonica, which probably isn’t reliably hardy below – 5 C (24 F). Pteris wallichiana has been grown successfully in the UK and Holland however, which is quite surprising. W. orientalis likely isn’t hardy much past USDA cold hardiness zone 8b.
They all need similar growing conditions, though the Woodwardia are decidedly woodland plants, requiring shade, while the Pteris like brighter conditions. P. wallichiana in fact can take quite a bit of sunshine. All like wetter sites in nature except W. japonica, which is never seen growing near water or on seepy ground. It needs well drained soil. The others can handle wet roots, but grow fine in evenly moist ground. None seem particularly fussy about the type of soil – any good woods loam with acidic reaction will do.
The fascinating habit of making asexual bulbs sets W. orientalis apart from most ferns. Once these develop triangular fronds they can be separated from the parent plant and put into trays of peat to grow on – a nifty way to propagate this one. P. wallichiana has proven to be easy from spore. The specimen in my garden spores freely and quite a few volunteer sporlings show up each year.
None are quite tree ferns, but all are large and lovely nonetheless. Both W. orientalis and P. wallichiana are available in the nursery trade, though the other two are likely to be quite rare outside their native range.