The most common and most likely answer to this crossword clue is the 6 letter word ALPINE
I've seen this crossword clue in The Guardian
A
L
P
I
N
E
More clues leading to the result ALPINE
- A large tree growing on high mountains
- Porter maybe carrying small drink up mountain
- Mountain elder in Massif Central holding record
- A large tree or small plant
- Pineal shaped plant of upland regions
- Almost all wood furniture is from the mountains
- A large tree, or a small plant
- Plant tree beyond outskirts of Arundel
- Clip opens beer from Germany, Austria etc
- Mountain of metal and wood
Buddy explains!

The straight part
We know that "Mountain" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case mountain = alpine.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ALPINE mean?
ALPINE noun- Any of several plants, native to mountain habitats, often grown in a rock garden
- Of, relating to, or inhabiting mountains, especially above the timber line
- Of or relating to slalom and downhill skiing. (Compare Nordic.)