The following is by no means exhaustive. If in doubt, don't bother!  

Acacia.

Clematis (Traveller's Joy).

Hemlock.

Nightshades.

Aconite.

Columbine (Aquilegia).

Henbane.

Orchid.

Alder.

Cotoneaster.

Holly.

Peony.

Anemones

Cow Parsley.

Honeysuckle. Except Flowers

Pheasant's Eye.

Aquilegia.

Cowbane.

Horse-Chestnut.

Poppy.

Arum Lilies.

Crocus.

Hyacinth.

Potatoes. Foliage.

Azaleas.

Crowfoot.

Hydrangea.

Privet.

Bane.

Cuckoo-pint.

Iris.

Ragwort.

Baneberry.

Cyclamen.

Ivy.

Rhododendron.

Belladonna.

Daffodil.

Jasmine.

Rhubarb. Except Stalks

Berberis.

Dahlia.

Laburnum.

Snowdrop.

Bindweed.

Deadly Nightshade.

Laurel.

Soapwort.

Black Nightshade.

Delphinium.

Lilac.

Spearwort.

Bluebell.

Dried Broom.

Lilies.

Spindle Tree.

Box Tree.

Dwarf Elder.

Lily-Of-The-Valley.

Spindleberry.

Broom.

Ferns.

Lobelia.

Sweet Pea.

Bryony.

Figwort.

Lucerne.

Thorn Apple.

Buckthorns.

Fleawort.

Lupin.

Tomatoes. Except For Fruit

Buddleia.

Fool's Parsley,

Marsh Marigolds.

Traveller's Joy.

Bulbs.

Foxglove.

Meadow Rue.

Tulip.

Buttercup Family.

Fungi.

Meadow Saffron.

Wood Anemone.

Campion.

Geranium.

Mercury.

Woody Nightshade.

Celandine.

Green Potatoes.

Mezereon.

Yew.

Charlock.

Groundsel.

Mistletoe.

Christmas Rose (Hellebores).

Hellebore.

Monkshood.

Chrysanthemum.

Hemlock.

Narcissus.