http://www.oxforddictionaries.com/definition/english/lichen says 'lichen' has two pronunciations: /ˈlʌɪk(ə)n/, /ˈlɪtʃ(ə)n/. In contrast, Oxford English Dictionary only registers the former. What is the history and distribution of these two pronunciations? (Which one do you use and where are you from?)
The /ˈlʌɪk(ə)n/ pronunciation is completely normal for how Latin words are pronounced in English. When an "i" is in a position where it would be pronounced as a long i in English, it often is: compare item, saliva, sinus, virus. And "ch" in Latin words (which is only found in originally-Greek words) is usually pronounced /k/ in English. Compare echo.
The /ˈlɪtʃ(ə)n/ pronunciation is probably a spelling pronunciation. Somebody reading lichen and never having heard it would be quite likely to pronounce it this way.
I can't find any data as to how these pronunciations are distributed geographically; one could look at the comments and see if there is any pattern. Living in the U.S. Northeast, I almost always hear /ˈlaɪk(ə)n/.
The OED has a note:
The pronunciation /ˈlɪtʃən/ is given in Smart without alternative, and most of the later Dicts. allow it a second place; but it is now rare in educated use.
The word is in origin Greek, not in use in English before the 18th century, although Philemon Holland’s translation of Pliny, of 1601, rather charmingly mentions that there is ‘a certain skinny gum, in Greek called Lichen, which hath a wonderfull operation to cure the rhagadies or chaps’. But in Benjamin Smart’s Grammar of English Pronunciation (1810), the "kitchen" pronunciation is the only one given.
Later, there came an alternative pronunciation (Li-Ken) based on the misconception that it was of Latin origin - such as "lichen simplex" or "lichen planus" - which are skin diseases.
So while pronouncing it to rhyme with KITCHEN is correct - the battle seems lost with LIKEN in common use.