One leaving trail heading north to escort advanced climbers (6)

'advanced climbers' is the definition.
The definition and answer can be both plants as well as being plural nouns.
Perhaps there's an association between them I don't understand?

'one leaving trail heading north to escort' is the wordplay.
'one' becomes 'an' (an apple is one apple).
'leaving trail' becomes 'sail' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'heading north' says the letters should be written backwards (in a down clue, letters travel north).
'to escort' is an insertion indicator (one word carries or escorts another).
'sail' in reverse letter order is 'lias'.
'an' placed within 'lias' is 'LIANAS'.

Can you help me to learn more?