# Lichen

F lichen 

Difficulty

1

Attacks

Touch sticky

F lichen 

Difficulty

1

Attacks

Touch sticky

Base level

0

Base experience

4

Speed

1

Base AC

9

Base MR

0

Alignment

0 (neutral)

Frequency (by normal means)

4 (Uncommon)

Genocidable

Yes

Weight

20

Nutritional value

200

Size

Small

Resistances

None

Resistances conveyed

None

A lichen:

 does not breathe.
 cannot pick up items.
 has no eyes.

 has no limbs.
 has no head.
 is mindless.

 does not eat. (*)
 is neither male nor female.
 is normally generated hostile.

Reference

monst.c#line1292

A lichen is a fungus-based monster that appears in Nethack, and is one of the easiest monsters to kill in the game. Their only attack is a sticky attack that holds the player in place briefly, but otherwise does no damage.
A "master lichen" is one of the many monsters that the player can see while hallucinating.

Contents

1 Strategy
2 History
3 Variants
4 Origin
5 Encyclopedia entry
6 References

Strategy
Lichen are extremely slow and easily beaten even by beginning characters; however, their sticky attack does prevent you from attacking any other target except the lichen, which wastes that turn ("You cannot escape from the lichen!") and forces you to focus on killing it first.
Unlike most corpses, lichen corpses never rot (though they do become old for the purposes of sacrifice), and can be carried indefinitely as normal comestibles which are always safe to eat. They provide 200 nutrition, but weigh the same as a food ration, so they should ideally be eaten first to free up carrying capacity. Lichen corpses are also valid food choices for vegans and vegetarians, and can be used to tame horses.
Dipping a lichen corpse into a potion of acid causes it to 'turn red around the edges', or orange if the potion is somehow diluted. This does not consume the potion.[1]

History
Lichen were added in NetHack 3.3.0.
NetHack 3.6.0 added messages when a lichen corpse is dipped in acid.

Variants
The arch-lichen patch by Nodey for NetHack 3.4.3 allows the variant known as the arch-lichen (based off the arch-lich) to be patched into a game. 

Origin

Wikipedia has an article about:
Lichen

Wikipedia has an article about:
Edible lichen

Lichen are composite organisms that arise from algae or cyanobacteria living among filaments of multiple fungi species. They can occur in many environmental conditions, including several extreme ones, and can grow on almost any surface. They also have a history of being used in real life as food, hence their potential use as sources of long-term food in NetHack. Real-life litmus tests use dyes extracted from lichens as a pH indicator, which is why lichen corpses in NetHack turn red when dipped into potions of acid.

Encyclopedia entry

The chamber was of unhewn rock, round, as near as might
be, eighteen or twenty feet across, and gay with rich
variety of fern and moss and lichen.  The fern was in
its winter still, or coiling for the spring-tide; but
moss was in abundant life, some feathering, and some
gobleted, and some with fringe of red to it.

[ Lorna Doone, by R.D. Blackmore ] 

References

↑ src/potion.c in NetHack 3.6.0, line 1949