One Thousand Magical Herbs and Fungi is a standard reference book about magical plants for potioneers.
This was on the list of required books for first years (PS5), and seems to be a required reference throughout a students' time at Hogwarts (GF10, OP17, HBP25). Some of the entries cross the line between plant and animal (e.g. flobberworm mucus) which emphasizes the fact that this book is essentially a potions manual.
Partial text of the book (Pm):
One Thousand Magical Herbs and Fungi
Dittany is a powerful healing herb and restorative and may be eaten raw to cure shallow wounds.
Flobberworm mucus is a popular potion thickener.
Aconite is sometimes called monkshood or wolfsbane.
Moly is a powerful plant that can be eaten to counteract enchantments. It is a black-stemmed plant with white flowers.
The cry of the Mandrake is fatal to anyone who hears it.
The Wiggentree is a magical rowan that will protect anyone touching its trunk from the attack of Dark creatures.
Never eat the leaves of the Alihotsy tree (also known as the Hyena tree). These leaves cause uncontrollable laughter.
The title of this book was given in error twice. In the first editions of Half-Blood Prince, the US version gave the title as A Thousand Magical Herbs and Fungi rather than One Thousand Magical Herbs and Fungi. In early British editions of Philosopher's Stone, the title is given correctly on Harry's "shopping list" in chapter five but given as One HUNDRED Magical Herbs and Fungi in chapter 14. Both of these errors have been corrected in later editions.