Hello Aspirant,

The best book for studying pharmacognosy is
C.K KOKATE ( Pharmacognosy) .
You can also study from theory and practicals written by J.S QADRY .
Some of the other books are :
1: Biren shah ( Pharmacognosy and phytochemistry)
2: Pharmacognosy fundamentals ,applications and strategy by Simone Nadal Mc.creath.
3: Pharmacognosy introduction by MS KOLHE ROHINI,

From all the above mentioned books i mostly used to prefer Pharmacognosy by C.K Kokate ,
The concepts in that book will be clear and easy to understand,

I hope the above information is useful to you ,

All the best !