Blechnum

The genus Blechnum has recently been split into multiple related genera, including Diploblechnum, Austroblechnum, Parablechnum and Cranfillia. For the medium term, we will keep them aggregated within Blechnum for the sake of these plant profiles, as it is interesting to be able to compare the differing growth forms of these related plants, and for consistency with the manner in which they are likely to continue to be referred to by horticulturists.

Within the landscape, flashes of bright colour are most commonly associated with the presence of flowers. However, there are other ‘events’ in the life of plants during which they produce vibrant tints – the most spectacular being the autumn leaves exhibited by many deciduous trees, before they fall (mostly in cold climates).

Such seasonal highlights can even be found amongst some unlikely candidates, our native ferns – a number of whom send forth new fronds that are emblazoned in bright red. This characteristic is particularly marked in members of the genus Blechnum (including B. montanum, pictured below), several of which are common fixtures in a variety of New Zealand’s ecologies.

The most commonplace of these, Blechnum novae-zelandiae, is perhaps the species that exhibits the most saturated hues (in a pinkish-red shade). It is one of the most willing colonisers of denuded banks, and its hanging fronds can be seen adorning many roadside cuttings throughout the country. Another species that used to be classified together with B. novae-zelandiae, Blechnum procerum, is worthy of special mention – for its new fronds assume an intriguing bronzish colour that lends it a distinguished appearance.

The genus Blechnum contains several fine plants for the garden – due both to their attractive appearance and their adaptability to a wide range of conditions. Traditionally, the most commonly-planted species (within general cultivation) are probably crown fern, Blechnum discolor, and water fern, Blechnum fluviatile. Ironically, both these species lack the distinctive colouration that is such a feature of the genus.

Blechnum novae-zelandiae is also familiar to many native gardeners, especially for sites where its enthusiastic growth habit can be used to best effect. For situations where a low-growing groundcover is required, B. penna-marina is also frequently used – particularly within the gardens of native plant enthusiasts. Of the remaining species, Blechnum minus, B. norfolkianum, B. procerum and B. vulcanicum are especially deserving of greater attention.

The name, Blechnum, is derived from the Greek word for a species of fern. Subsequently, it became a more general term for ‘fern’, within Latin¹. Blechnum spp. are often referred to by the common name, ‘hard ferns’. It is a large genus (with in excess of 150 species) which is mostly centred in the Southern Hemisphere.

We are so accustomed to the look of grass or creeping herbs (like thyme) as groundcovers that there is something quite unexpected (and a little magical) about the sight of a carpet of ferns. In New Zealand, we have a number of fern species that conform to this growth habit; and amongst these, Blechnum penna-marina is the most compact and uniform.

This lovely little fern grows in a wide range of mostly open habitats, throughout much of the country (although it is more common in southern parts of the country). It is by no means confined to New Zealand – for it also occurs in Australia and at the cooler, southern end of South America.

At this point, I will diverge from the specific matter of B. penna-marina, to explain a related story regarding the cultivation of native plants. The botanist, Leonard Cockayne (one of New Zealand’s great historical figures), had a very interesting experimental garden, called Tarata, next to the coastline at Christchurch. At Tarata, Cockayne made a point of sometimes growing plants in spots that differ from their normal growing stations; such as planting a swamp plant at the top of a sand dune.

This does not mean that he ignored the valid lessons that can be gleaned from accurate observation of the way in which plants grow in the wild. Cockayne was interested in looking into the full range of tolerances of certain plants, and avoiding assumption (albeit in an informed manner). In all likelihood, he expected himself to be proven wrong in a great number of cases – but it must be remembered that Tarata primarily performed an experimental function.

What is the point of this little story ? That we can sometimes assume that a plant will not grow in a particular place or climate (based on its wild habitats), and be proven completely wrong. Early on in my gardening life, I had assumed that a plant called alpine hard fern, with a low, spreading system, would struggle in the humid north. I was wrong (of course, if I’d just listened to Terry Hatch in the first place, I would have known that).

One of the most endearing features of B. penna-marina is the appearance of the pinkish-red new foliage early in the growing season. It forms beautiful carpets of upright fronds, usually to about 10cm tall, in a subtle olive-green hue.

Despite the name, alpine hard fern, it grows to sea level in parts of its natural range, and occurs in environments ranging from boggy ground to relatively dry conditions. Although it thrives in a variety of habitats, it achieves its thickest growth in comparatively open conditions; and one of the few provisoes regarding its use in gardens is that it is least suited to planting in heavy shade.

As noted in the profile on B. penna-marina, innovation often requires casting aside supposedly logical assumptions, and testing things for yourself. This is demonstrated by several nurserypeople, such as Terry and Lindsey Hatch, who explore the real versatility of species by growing forms from different areas and habitats. Such observation and experimentation serves as a reminder that species are a conceptual group that we define, rather than a uniform product, and can contain a significant amount of diversity (and therefore, tolerances) within them².

Another nurseryman who refuses to accept conventional wisdom as rote is Jeff McCauley, who has developed an intense knowledge of Auckland’s regional flora over the last decade (in addition to an already considerable fascination with NZ’s overall flora).

This creeping fern, Blechnum procerum, is a perfect example of the benefit that can be derived from such an approach. Although it is mostly associated with areas south of Auckland (or higher altitudes where it occurs in the north), Jeff has propagated several forms that have proven to be excellent garden plants for normal situations within Auckland. It also defies some descriptions of the species by growing equally well within open aspects as it does in the shade³, as well as tolerating a range of moisture regimes.

In the Waitakeres, Blechnum procerum is found in a number of localities, notably at higher points or colder areas – such as the track near Nihotupu Dam where the photographs above were taken. Taxonomically, the species has had a confused history, as it and several other species were previously lumped in with each other in a large, ill-defined species complex.

Upon viewing B. procerum in the wild, this seemed a much more understandable state of affairs, as there exists a spectrum of hybrids (with B. novae-zelandiae) along the track (that make it hard to discern where the limits of the species begin and end⁴). Some of these hybrids have the potential to be horticulturally valuable, as they combine desirable characteristics of both species.

The bronze colour that the new fronds exhibit is particularly beautiful, and achieves its most intense colouration within an open spot. As a creeping fern, this is one of a number of species that interests us for the establishment of fern ‘meadows’ as a groundcover type within gardens.

To maintain a lush cover, it is a good idea to regularly apply nitrogen-based fertiliser, even though B. procerum seems reasonably tolerant of low fertility in its natural growing stations.

B. procerum is found throughout most of the botanical province of New Zealand (with the exception of the Kermadec Islands and the northern tip of Northland), and is only found upon our shores. It is found in a wide range of habitats, from swamp forest to subalpine grassland. Although it can grow as high as 90cm (especially the fertile fronds), it more typically attains a height of 30 to 50cm – hence, the common name, small kiokio.