Blechnum fluviatile - Ray water fern

Blechnum fluviatile is an exceptionally ornamental New Zealand fern. Nicknamed the star fern, it displays rosettes of elongated fronds with ovate to almost round pinnae, giving it a truly unique appearance. The rich green sterile fronds open elegantly to create a spreading effect, while the fertile brown fronds rise almost vertically from the centre. Thriving in humid climates, in humus-bearing, slightly acidic soil and partial shade, it shows decent hardiness, down to -10°C.

Blechnum lends its name to the small Blechnaceae family, which includes 23 other genera of ferns naturally distributed across much of the Earth's surface. Several family members are prized in gardens, such as Woodwardia fimbriata, with its lush, deeply divided foliage. The Blechnum genus comprises around 200 species, mostly native to the Southern Hemisphere (New Zealand, Australia, Chile). Their growth consists of evergreen, pinnate fronds, meaning they are divided on a single level, with the central vein of the frond supporting pinnae equivalent to leaflets in compound leaves (e.g., Black Locusts). Some ferns, like the ostrich fern or Matteuccia pensylvanica, are bipinnate, as their pinnae are further divided into pinnules, giving these plants a very feathery appearance. In the Blechnum genus, erect fertile fronds with narrow pinnae contrast with more spreading sterile fronds featuring broader pinnae.
Blechnum fluviatile (synonym Cranfillia fluviatilis) was identified relatively recently, in 1979, by a New Zealand botanist specialising in ferns. However, the species is not exclusive to New Zealand, as it is also found in southeastern Australia, Tasmania, Borneo, Papua New Guinea, and Sumatra. In New Zealand, it grows up to 1,150 metres in altitude across lowland and mountainous regions, except in dry areas. It particularly favours beech forests, Agathis (a conifer endemic to the North Island), Podocarpus, and occasionally pine or willow stands. It thrives in moist, shaded forest soils, along waterways, lakes, or marshes, and in damp meadows. It spreads gradually via a network of rootstocks.
In gardens, Blechnum fluviatile grows slowly, forming a rosette 50 cm tall and 80–100 cm wide. Dimorphism is pronounced in this species: the sterile fronds are a vibrant green and flexible, while the dark brown fertile fronds are stiff, rising almost vertically from the plant's centre. Measuring roughly 50 cm long, the sterile fronds are very narrow, no more than 5–6 cm wide. The frond's rachis (central vein) is a reddish-brown shade, covered in hairs, and lined with ovate to rounded, slightly crinkled pinnae. The fern's striking appearance vividly evokes distant subtropical landscapes.

Blechnum fluviatile is well-suited to Atlantic coastal areas, where it will find the humid conditions it loves, along with mild winters. You can easily create an exotic display by pairing it with other distinctive plants, such as Fatsia, a small bush with stunning palmate foliage that also thrives in shade and cool conditions. A few clumps of Farfugium, a perennial with remarkable foliage, will enhance the scene beautifully. For a splash of colour, consider Hedychiums or ornamental gingers, whose lush green leaves and vibrant flower spikes evoke the Tropics.