The autumn fern, Dryopteris erythrosora

Japan and much of southeast Asia’s broad leaf evergreen forests are home the autumn fern, Dryopteris erythrosora, who’s claim to fame is the brilliant red of its newly grown fronds.  This is one of the most commonly grown Japanese ferns due to its beauty and ease of cultivation.  In the woods near my home on Kyushu, it is a near weed.

Dryopteris erythrosora habitat
The autumn fern is at home in just about any forest type on Kyushu, and ventures out to roadsides as well. Here it is growing in a hinoki plantation forest.

Dryopteris erythrosora is a medium to large sized evergreen fern with a short, creeping rhizome.  The glossy fronds are twice pinnate with the pinnules ending in a pointed tooth and are 30-130cm long and 20-40cm wide.  The emerging croziers are bright brick red, and the newly grown frond retains this color for a short time before assuming the dark green of a mature frond.  The stipe is covered with many brown scales and accounts for 1/3 of the frond length.  The brick red sori are round and numerous, occurring in pairs on the pinnae’s lobes on opposite sides of the costa. The indusia are kidney shaped.

Dryopteris erythrosora new frond
As the new frond of Dryopteris erythrosora expands it has a deep, brick red color. This is why the Japanese call it benishia, meaning “red fern”.

In Japan D. erthrosora is found in the broad leaf evergreen forests of Honshu, Shikoku, and Kyushu.  It is also native to China, Korea, and the Philippines.  On Kyushu it is a common fern at almost any altitude being seen in moist forests, tree plantations, cut over hillsides, growing in rock walls, and roadsides, from 0 to 1000+ meters.  It is a clumping fern found in loose colonies.

Dryopteris erythrosora sori
The sori of Dryopteris erythrosora are bright brown-red. In fact, erythrosora means “red heap”, no doubt in reference to these.

This is certainly one of Japan’s better known ferns often sold under the name autumn fern because of the rich red color of the new fronds.  The Japanese name literally means “red fern”, alluding not only to the emerging crosiers and newly grown fronds, but also to the young ripe sori that too are bright red-brown.  This plant is common throughout my local area in just about any woodland or roadside.  In time it can grow into large clumps with fronds over a meter long, but most often is it more modest in size.  Without a doubt, the most striking feature of this plant are the newly emerged fronds starting out a rich red color, then turning lime green, and finally dark green with maturity.

Dryopteris erythrosora half grown frond
The newly grown fronds of Dryopteris erythrosora retain much of their red color for several weeks after flushing.

Its Japanese name is benishida, meaning “red fern” from the words beni (crimson or red) and shida (fern).  The Latin species epithet, erythrosora, comes from the Greek words “erythros” meaning red and “sori” meaning “a heap”, no doubt a reference to the round, red sori of this species.

Autumn fern is easily grown in just about any garden setting except full blazing sun.  It seems to adapt well to just about any soil as long as it is free draining and not too basic in reaction.  It should be fully cold hardy from UDSA zones 5-10, though it may defoliate in colder zones.  This is not a picky species and worth growing for the spring fronds alone.

Dryopteris erythrosora crozier
Even the crozier of Dryopteris erythrosora shows off red color – this will deepen as it expands.


Leave a Reply

Your email address will not be published. Required fields are marked *