There's nothing in manuscripts of botanical interest (4)
I believe the answer is:
moss
'manuscripts of botanical interest' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'there's nothing' is the wordplay.
I cannot quite see how this works, but
'nothing' could be 'o' (looks like zero - 0) and 'o' is found in the answer.
The remaining letters 'mss' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'in' acts as a link.
Can you help me to learn more?
(Other definitions for moss that I've seen before include "Shape of pointed arch" , "Plant forming most of my lawn!" , "Plant reproducing by spores" , "Former racing driver" , "Small flowerless plant(s)" .)