Dungeon fern

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The dungeon fern is an unassuming monster appearing originally in UnNetHack, though versions of it have also been incorporated into dNetHack, Slash'EM Extended, and SLASHTHEM. It is sessile and has no physical attacks. However, when approached, it creates dungeon fern spores, the more dangerous cousins of gas spores.

Dungeon fern spores attack their targets directly by bursting into stinking clouds. The explosion itself does no harm to the target, and the dangerous effects of the cloud are entirely mitigated by poison resistance or unbreathing. If you do not have either of these, standing at a diagonal to the spore when it bursts will give you a significant chance of being outside of the cloud when it forms. Attacking directly will cause the spore to explode properly, just like a gas spore.

Exploding dungeon fern spores have a 1 in 3 chance of creating a new fern. There is a 1 in 6 chance that it will be a full-grown dungeon fern[4]; otherwise, it will be a dungeon fern sprout, a lower level dungeon fern which produces spores at a lower rate. It is important to destroy both kinds of ferns quickly unless you possess the means to contain out-of-control growth.

Dungeon fern spores will target other monsters as well as the player, and in turn other monsters will attack fern spores on sight[5]. A careful player can take advantage of this and lure spores toward otherwise difficult monsters without poison resistance.


UnNetHack features four different species of fern: the regular dungeon fern, the arctic fern, the blazing fern, and the swamp fern. The main differences among the four species are the types of damage caused by their exploding spores, and the terrain in which they can reproduce[6].

Dungeon fern

The regular dungeon fern produces spores that deal physical damage when they explode. These spore explosions can produce new ferns and sprouts on floor and muddy swamp tiles.

Arctic fern

The arctic fern (F) resists cold damage, and its spores (e) deal cold damage when they explode. New arctic ferns and sprouts can only grow on water, ice, or swamp tiles.

Blazing fern

The blazing fern (F) resists fire damage, and its spores (e) deal fire damage when they explode. New blazing ferns and sprouts can only grow on lava tiles.

Swamp fern

The swamp fern (F) produces spores (e) that deal physical damage when they explode, like the dungeon fern. However, they will only produce new swamp ferns and sprouts on swamp tiles.

In the Ruins of Moria, there is a 25% chance that a fraction of the tiles on the Forest level will be swamp. If so, four swamp ferns will be generated throughout the level[7].

Fern spore

In UnNetHack, reading a blessed scroll of stinking cloud while confused will generate up to three nonspecific fern spores (e), which can produce any of the four species of ferns, on appropriate terrain. (Reading a non-blessed scroll produces gas spores instead[8].) These spores are not otherwise randomly generated.


In UnNetHack, ferns are part of the F monster class, which is defined (according to the what is and farlook commands) as "fungus, mold, or fern". In dNetHack they are part of the plant class, which uses the { glyph. In Slash'EM Extended and SLASHTHEM they use the % glyph, like the evil food monsters from SLASH'EM.

Two types of ferns appear as monsters in dNetHack, along with their respective spores and sprouts: the dungeon fern and the swamp fern (here {). The former is identical to its UnNetHack counterpart, but the explosion of the dNetHack swamp fern spore (e) deals 4d8 damage instead of 2d4, and causes fungal diseases.

A user has suggested improving this page or section as follows:

"Any other differences in Slash'EM Extended and SLASHTHEM?"

Real life

Ferns are a group of real plants with characteristic leaves. They are primitive, having neither seeds nor flowers, reproducing with spores. Hence the spore attack in the game.

Encyclopedia entry

These dreadful weeds have been driven to extinction on the
surface, yet deep within the dark and damp of the dungeon
they still flourish. When it detects the motion of nearby
creatures, the dungeon fern releases a deadly, poisonous
spore, which quickly detonates to propagate the species.

Residents of the dungeon have learned how not to disturb
the dungeon fern, and will attack its spores on sight to
keep them from overtaking their home.


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