Abyssinian shrivelfig
When peeled, shrivelfigs are used as an ingredient in Shrinking Solution.

Aconite(monkshood, wolfsbane)
An extremely poisonous plant (hence the name wolfsbane). The name monkshood comes from the shape of the flowers.
Ellis Peters’ medieval mystery Monk’s Hood, the third entry in the Brother Cadfael series, is recommended as both a very good story in its own right and as featuring both the positive and dangerous aspects of this plant. The herbalist Cadfael used the plant as part of an oil used to massage aching joints, but if swallowed or absorbed directly through any break in the skin, the oil could be deadly.

Alihotsy
Eating the leaves causes hysteria.

Asphodel
A key ingredient of the Draught of Living Death, this plant is traditionally associated with the afterlife and the underworld.

Belladonna
The essence of this poisonous plant is part of a student’s standard potion-making kit.

Bouncing bulbs
Repotted during Herbology class, one wriggled free from Harry’s grasp and banged him in the face.

Bubotuber
A bubotuber looks like a thick, black, giant slug (it even squirms slightly, although it sticks vertically out of the soil) with many large shiny swellings on it that are filled with yellow-green pus that smells like petrol. As Professor Sprout taught her fourth-year students, the pus reacts oddly with human skin. Undiluted, it will raise horribly painful boils on contact, but properly diluted and processed can be used to cure acne.

Cabbage
Hagrid maintains a cabbage patch for Hogwarts, presumably to supply the school kitchens. According to Hagrid, flesh-eating slugs have been known to get into them.

Daisy
Chopped, the roots are an ingredient in Shrinking Solution.

Devil’s Snare
Devil’s Snare is composed of a mass of soft, springy tendrils and vines that possess some sense of touch. Devil’s Snare uses its creepers and tendrils to ensnare anyone who touches it, binding their arms and legs and eventually choking them. The harder a person struggles against Devil’s Snare, the more faster and more tightly it binds them; if they relax, it will not kill them as quickly. Devil’s Snare prefers a dark, damp environment and shrinks away from fire, so a well-placed flame spell such as Bluebell Flames will drive it away from its victims.

Dittany
One of the plants found in One Thousand Magical Herbs and Fungi, and which historically has indeed been believed to have magic powers.

Fanged Geranium
This plant, which will bite humans, turned up on Harry’s Herbology O.W.L.

Flitterbloom
This plant apparently superficially resembles Devil’s Snare in appearance, but is non-violent; St. Mungo’s healer Miriam Strout mistook the Devil’s Snare that killed Broderick Bode for a Flitterbloom.

Flutterby Bush
This kind of bush quivers and shakes. The Flutterby bushes needed pruning in herbology class
“flutterby” is sometimes used in English as a play on the word “butterfly”

Fluxweed
An ingredient in Polyjuice potion, but has to be picked at the full moon to be effective therein.

Gillyweed
Native to the Mediterranean, this water plant looks like a bundle of slimy, greyish-green rat tails. When eaten, gives a person gills to breathe underwater and gives them webbed hands and feet for swimming. The duration of the gillyweed effect is approximately one hour. Snape keeps gillyweed in his private stores; it is not available to the students.

Ginger
The roots are an ingredient in Wit-Sharpening Potion.

Hellebore
A poisonous plant occuring in several varieties.

Holly
A species of tree that qualifies as a “wand tree”, in that its wood can be used in the making of magic wands. Holly is a traditional symbol of resurrection, but in a much more upbeat sense than yew (being associated with Christmas rather than cemeteries helps its image considerably).

Honking daffodil
Sprout has some, but Lavender Brown, for one, prefers mundane daffodils.

Hornbeam
A species of tree that qualifies as a “wand tree”, in that its wood can be used in the making of magic wands.

Knotgrass
An ingredient in Polyjuice potion.

Leaping toadstool
The second-year Herbology classes worked with these.

Lovage
Used in Confusing and Befuddlement Draughts.

Mallowsweet
Centaurs burn this, observing the fumes and flames to refine the results of their stargazing.

Mandrake(Mandragora)
The Mandrake root is a powerful restorative. It forms an essential part of most antidotes, including one for Petrification. The Mandrake Restorative Draft returns people who are transfigured or cursed to their original state. Mandrake seedlings are tufty little plants, purplish-green in color with what looks like tiny babies growing where the roots would be. These creatures grow and develop over the course of several months until they mature and can be harvested and used for potions. The cry of the Mandrake is fatal to humans, so special care must be taken when growing them. Even as a baby, the Mandrake’s howls can knock a person out for a couple of hours.
The Dugbog is particularly fond of eating Mandrakes.

Maple
A species of tree that qualifies as a “wand tree”, in that its wood can be used in the making of magic wands.

Mahogany
A species of tree that qualifies as a “wand tree”, in that its wood can be used in the making of magic wands.

Mimbulus Mimbletonia
Very rare, native to Assyria, this plant resembles a grey cactus, but with boils where the spines would have been. The boils are a defensive mechanism that spews Stinksap upon contact.

Nettle
An ingredient featured in a simple potion used to cure boils.

Monkshood
See aconite.

Oak
A species of tree that qualifies as a “wand tree”, in that its wood can be used in the making of magic wands. Oak is a common symbol of strength.

Privet
One of only two English representatives of the olive family, this very boring plant is often grown in Muggle suburbs to form hedges.

Puffapod
Fat pink pods with seeds that burst into flower if dropped.

Pumpkin
Hagrid maintains a pumpkin patch outside his hut, which produces the pumpkins used to decorate the Great Hall for the Halloween feast. Although the plants aren’t inherently magical, Hagrid gives them some “help” so that the pumpkins swell to the size of garden sheds by the time the feast rolls around.

Rosewood
A species of tree that qualifies as a “wand tree”, in that its wood can be used in the making of magic wands.

Sage
Centaurs burn this, observing the fumes and flames to refine the results of their stargazing.

Screechsnap seedlings
Semi-sentiant plants which wriggle and squeak uncomfortably when they are given too much dragon dung manure. The fifth years work with this plant in Herbology.

Scurvy-grass
Used in Confusing and Befuddlement Draughts.

Self-fertilising shrubs
Harry and other fifth years had to write an essay on self-fertilising shrubs for Professor Sprout.

Sneezewort
Used in Confusing and Befuddlement Draughts.

Umbrella-sized flowers
Hanging from the ceiling of greenhouse 3

Venomous tentacula
Spiky, dark red – teething, reaches out vines toward people

Willow
A species of tree that qualifies as a “wand tree”, in that its wood can be used in the making of magic wands.

Whomping Willow
A species superficially resembling the willow, this large, violent tree attacks anyone who gets too close.

Wolfsbane
See aconite.

Wormwood
A key ingredient of the Draught of Living Death (PS8). Interesting that this traditional symbol of bitterness featured prominently in the first question Snape ever set Harry in Potions.

Yew
A species of tree that qualifies as a “wand tree”, in that its wood can be used in the making of magic wands. Yew trees are symbolic of death and resurrection – the wood is particularly resistant to rotting – and were once a traditional feature of churchyards.