Bird sitting on spike, tall flower (8)

I believe the answer is:

larkspur

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'tall flower' is the definition.
'larkspur' can be an answer for 'flower' (larkspur is a kind of flower). I'm not sure about the 'tall' bit.

'bird sitting on spike' is the wordplay.
'bird' becomes 'lark' (lark is a kind of bird).
'sitting on spike' becomes 'spur' (I can't explain this - if you can you should give a lot more credence to this answer).
'lark'+'spur'='LARKSPUR'

Can you help me to learn more?

(Other definitions for larkspur that I've seen before include "Blue flower" , "Plant with flower spikes" , "Delphinium-like plant" , "Mediterranean plant of the buttercup family" , "in bed!" .)

I've seen this clue in The Telegraph.

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