The common names for this fern are the ‘Fishbone Water Fern’ (although sometimes this gets shortened to simply the ‘Fishbone Fern’) and the ‘Black-stemmed water fern’. The species gets the common name ‘fishbone water fern’ from its fronds, inparticular the fertile fronds which look like fish bones. The species is native to Australia and is one of the most common ferns growing abundantly across all states apart from the Northern Territory and Western Australia. As its common name the ‘Fishbone Water Fern’ would suggest the fern likes water and is often found growing along streams and creeks. The picture below was taken at Badgers Creek in the Yarra Valley in Victoria, where Blechnum nudum can be seen growing alongside the creek.
Blechnum nudum has bright-green fronds that can grow up to a metre long in length. The species can grow trunk up to 1 metre tall with multiple trunks or growth points on the same plant. This species is dimorphic as with many of the other Blechnum species and the sterile fronds appear erect growing from the centre of the crown in spring. Blechnum nudum can be identified from the fertile fronds will grow from a deep black stem. Blechnum nudum will often spread and develop large colonies in the under story of its larger cousins Dicksonia antarctica and Cyathea australis. The picture below is another shot from Badgers creek this time if you look carefully you can see Blechnum nudum growing almost in the creek with larger Dicksonia antarctica and Cyathea australis tree ferns surrounding it and large Eucalyptus regnans tree in the background.
Until the harsh winter of 2011 experiences in England I would have said this fern is hardy to around -4°C (25°F) however we experienced temperatures down to around -10°C (14°F) and the fern showed no ill effects. Maybe the area of my fernery this specimen was in has its own micro climate but I would say that once established it should be hardy to at least -4°C (25°F) and if you mulch plants in the autumn as mine where it may take a few degrees more frost.
This fern does like a good amount of water and is even happy to be sat in water unlike many ferns that need moisture and drainage. Therefore this Blechnum nudum is always a good specimen to plant up against more established tree ferns. If planting larger trunked tree ferns I wouldn’t be scared to plant Blechnum nudum in the same hole, I often find that the dense roots Dicksonia antarctica produces help a colony of these to fill in the undergrowth quickly ensuring that ‘just planted’ look of bare earth soon disappears into a well established planting scene.