Queen Anne’s Lace
If brought into the house, snakes will follow it. In Yorkshire, this is known as Mother Die, or Stepmother's Blessing, since if it's brought into the house, your mother will die.
Bindweed
This was also known as Thunder Flower, since if you picked it, it would thunder before the day was out. This power was also ascribed to the poppy.
Hawthorn
Besides its association with fairies, this plant was considered bad luck in the house, since it either indicated a sore throat or a dead child.
May Flower
This back luck flower, if picked, meant you wouldn't get any apple crop, and that it would rain all summer long.
White Heather
This was considered unlucky by Scottish loyalists because of its connection with the banishment of Bonny Prince Charles.
Mimosa
In the house, it is considered a forewarning of disaster.
Herb Robrt
If picked, snakes emerged from the stem.
Primrose
It was considered unlucky to pick these if it was before the chicks hatched, since the number of primrose blossoms picked indicated the number of chicks that would be born from each clutch. So if you picked primroses, you had to pick a lot. Thirteen was considered the optimal number.
Blackthorn
This is unlucky to pick because a scratch will cause blood poisoning.
Stag's Horn Sumac
If this is growing in the garden, it brings marital strife. The same is said of Matrimony vine.
Ivy
Ivy is unlucky as a gift and a person who keeps ivy will always be poor. The saying in Ireland is: "The house where ivy grows will surely fall."
Ivy may be brought in as Christmas decorations, but if it is not removed by Candlemas, death will visit the household.
Blackberries
These cannot be picked after Michaelmas, since after that they 'have the devil in them'.
Elder
In Ireland, it was thought an Elder tree growing in the yard make the inhabitants prone to consumption.
Broom (the plant, not the cleaning implement)
If brought into the house, it 'sweeps someone out'.
Speedwell
If you pick the flowers, birds will come and pick your eyes out.
Privet
It was rumored that privet leaves were one of the sources of diphtheria.
Sassafras
If you burn the wood, and it cracks and sputters, then someone will die.
Gray Pine
This is called the "Unlucky Tree" because anyone who stands underneath it will misfortune befall them. It is supposed to affect women more.
Puff-Ball
These are thought to be poisonous to the touch, to give you the itch, or if the powder gets in your eyes, to blind you.
Bog Asphodel
This is considered unlucky because it 'softens the bones'.
Sundew
Also known as "Red Rot" because it 'rotteth sheep'.
Innocence
If you gather the flowers of this plant, it will make you wet the bed. The same is said of dandelions.
Moonwort
This plant had the country name of Unshoe-the-Horse, because it was thought that any horse that trod upon it would become unshod. This was also a property of Rest Harrow and Horseshoe Vetch.
Cuckoo Pint
If young girls touch it, they will become pregnant. The Cuckoo-flower, also known as Lady's Smock, was also considered unlucky because it was associated with the Devil.
There were many plants generally associated with ill luck or death, such as snowdrops, beefsteak geraniums, cacti (in Hungary), lilacs, and any flower usually associated with funerals, such as chrysanthemums or lilies. It is unlucky to pick up flowers which have dropped on the ground. And any flower that blooms out of season is considered 'touched by the devil'.