Within the nearly sopping wet subtropical low elevation forests of southern Japan one can easily find ferns growing not only in the ground, but also on every imaginable perch. This article focuses on four species that are found either growing on rocks (lithophytic habit) or on trees (epiphytic habit), but that can also colonize soils, in particular the moist or even wet ground near mountain streams.
As one might expect, such places give the impression of the lushness of a tropical rain forest, however such forests are in fact temperate, albeit with a strong influence of subtropical flora. First, we’ll look at the genus Neocheiropteris, represented in the forests of Fukuoka Prefecture by two species, N. enstata, and N. subhastata, the former being a conspicuous ground and rock fern in many forests while the latter showing itself to be a shy cousin with great flexibility in habitat choice.
N. enstata at first glance might be mistaken to be a species of Pyrrosia. That is what I thought it was the first time I saw it. It grows either as a lithophyte or terrestrially, but always in a place with abundant water (one thing that sets it apart from Pyrrosia which like drier sites).
Along streams it can form lush mats on top of flat rocks, however, it is just as happy to grow in the ground. I’ve not seen it growing as an epiphyte in the Fukuoka area, but in exceptionally wet climates it could possibly grow in trees. Occasionally colonies can be continuous carpets of fronds. Another place you sometimes find it is on rocks on seepage slopes. Here the plants never dry out and in fact the roots are nearly under water much of the growing season. The large, broad shiny leaves are deeply ribbed making it an attractive plant. The round, naked sori are in lose pairs on either side of the midrib of the frond, a diagnostic feature. It is usually seen at low elevations, not more than 400 meters high in the Fukuoka area.
A far rarer fern than its common relative, N. subhastata can be found growing low on trees, on rocks, and also in the ground. I first found it growing low on trees next to a stream, and even growing on dead bamboo canes. At first I thought it was Microsorium buergerianum, a fern it closely resembles, although when seen side by side the differences are obvious. These plants had simple elongate fronds with undulating margins and sori resembling both Microsorium and N. enstata. Further upstream from these was a colony of very small ferns with distinctly triangular fronds growing over a mossy rock surface and terrestrially. I immediately remembered seeing this fern in a picture and guessed it to be N. subhastata.
I returned time and again to look for spore on these plants, but I could never find any. One day, a little further downstream, I saw some of this same triangular frond fern growing in humus on a huge boulder. I followed its trailing rhizome and remarkably as it grew out of the humus and became a true lithophyte on the rock surface, the fronds “turned into” the elongate frond fern I found downstream. I immediately saw my mistake and realized that this was indeed one species with two distinct frond types.
The terrestrially growing fronds are short, triangular, and sterile while the lithophytic or epiphytic fronds are elongate and fertile and have a small auricle on one side of the base of the frond. Like E. enstata, the sori are in round and naked in lose pairs on either side of the midrib of the frond. This is a much smaller species than N. enstata, so the two cannot be confused. This species seems to require high humidity to survive. I’ve only seen it at low elevation, ~300 meters or less.
The next species, Microsorium buergerianum, can easily be confused with N. subhastata, which it resembles closely. The differences between this plant and N. subhastata include: its fronds are generally much longer and broader, it has no auricles at the base of the fronds, the blade ends completely at the joining of the stipe (the blade in N. subhastata grows wing-like down the stipe), the stipe is relatively long, the frond’s surface is more glossy, and the margins of the fronds are completely even with no undulations. One key diagnostic feature are the sori, which are round and naked like N. subhastata, but occur in a random pattern over much of the frond rather than in pairs.
This fern seems to require a very moist habitat next to flowing water and grows low to the ground, no more than a meter or two up a tree or bush. It is an uncommon species in the Fukuoka area in my experience since to date I have found just two small colonies in separate valleys. Here it is locally abundant and grows sprawling over the ground and rocks, clinging onto the branches of shrubs, and on the trunks of large trees. No doubt this is a plant of tropical origin at the northern edge of its range in Japan. It is a rare fern of relatively warm, humid forests in the vicinity of streams, ~ 0-200 meters elevation.
The last fern, Diplazium subsinuatum, always seems associated with running water. It loves to grow in ravines cut by small streams where it commonly forms large colonies carpeting these nearly vertical banks. At first glance one can be tricked into thinking it to be a species of Pyrossia or Neocheiropteris, but an examination of the sori pattern will immediately dispel that idea, since they grow in distinct, even rows at a 45 degree angle to the frond’s midrib. The top of the fronds have an uncanny ability to look blue due to their intense sheen. This plant is neither common or rare in the Fukuoka area, but widely distributed. It is always found along water courses or seeps growing either terrestrially or as a lithophte. In particular it seems to like the steep banks and rocks around water falls. In short, this fern is a water lover. In Fukuoka it is found at fairly low elevations, ~100-300 meters.
I have grown each of these species with ease at my house. N. enstata will grow well perched on a rock as long as you keep it moist and humid, otherwise it will desiccate. Unlike true epiphytes, this species is not tolerant of drying out much. The same can be said of N. subhasta, in fact I have not been successful growing it mounted in my urban garden. It grows nicely however in the ground, or better yet in pot of peat moss perlite. M. buergerianum seems to do just find mounted or potted, as long as the medium doesn’t stay perennially sopping wet. This is definitely the most epiphytic in nature of the four ferns discussed here. D. subsinuatum is of course another water lover, but grows happily in an evenly moist mix of peat, perlite, and loam. Another compost ingredient is kanuma, a volcanic material that looks somewhat like pumice, but is much softer and has a yellow-orange color. It is acidic in reaction, a thing most ferns like. When mixed with peat moss, virtually any fern’s roots go bananas, so that is my basic compost for all types of fern.
See many of these species in the wild in this video:
Given their tropical origins, these ferns probably have relatively little cold tolerance. In my garden temperatures can go to – 5 C (24 F) on occasion, and this doesn’t seem to bother them. In their mountain homes they probably see a degree or two colder than that, but none want to have crystalline frost develop on their fronds. Average winter temperatures should remain above freezing, however warm winter conditions are not needed. As long as the average is above 3 C (37 F), they will be fine. Using the USDA cold hardiness zones, I would guess that zone 9 would be optimal, and 8b acceptable with protection during hard freezes. One thing they all demand is frequent watering and high humidity. All are interesting plants that can add tropical flavor to subtropical or warm temperate gardens.