Material of which there are fifty-nine varieties (5)

I believe the answer is:

linen

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'material of which there' is the definition.
'linen' can be an answer for 'material' (linen is a kind of material). I'm unsure of the remainder of the definition.

'fifty-nine varieties' is the wordplay.
'fifty' becomes 'l' (Roman numeral).
'varieties' indicates anagramming the letters (I've seen 'variety' mean this).
'nine' with letters rearranged gives 'inen'.
'l'+'inen'='LINEN'

'are' acts as a link.

Can you help me to learn more?

(Other definitions for linen that I've seen before include "Flax product" , "Flaxen cloth" , "Flax textile" , "Cloth woven flax fibres" , "Such paper" .)

I've seen this clue in the Evening Standard.

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