Aloe (Aloe barbadensis) common
name Aloe Vera. As with Aloe arborescens, ingestion of the latex
can cause a cathartic (purging) reaction by irritating the large intestine.
Aloe is a popular house plant due to its reputation as a healing plant for
burns, cuts and other skin problems but contact dermatitis can occur in sensitive
individuals. If you use Aloe, you should cut away the skin and inner
layer of yellow juice leaving only the actual gel. The yellow juice, especially
prominent in older plants, is the primary irritant in the cases of contact
dermatitis. You should test a small area of skin, such as the inner forearm,
for a reaction before more general use. Aloe is also an air purification
plant.
Amaryllis (Amaryllis sp.) Amaryllis is grown indoors for its showy Autumn/Winterblooms. The principal irritant (alkaloids) is present in small amounts so large quantities of the bulb must be eaten to cause symptoms which include diarrhoea, nausea and vomiting.
Apples People do not
realise that apples, as well as common fruits such as cherries, plums, almonds,
pears, peaches, and apricots, are related to roses. Fewer people still
realize that all the seeds of these plants & their wild relations are
poisonous, though children are traditionally warned to avoid eating apple
seeds - with good reason. The pulp of the fruits themselves is safe.
Greatest concentration of the toxin occurs in vigorous growth shoots, seeds
& wilted leaves. Main toxin: Glycoside, producing cyanide.
The seeds, bark & leaves contain a cyanide-producing compound called
amygdalin. In addition, wild cherries (chokecherries) produce prunasin, a
similar compound. Cyanide is associated with the smell of bitter almonds,
but commercial almond oil is always treated to remove the cyanide. Poisoning
can occur by consumption of young shoots, leaves, and/or quantities of seeds
by livestock or children. Wild cherries, the berries of the closely related
Mountain Ash, & rose hips are more likely causes than domestic fruits,
as the seeds, pits & stones of the latter are too large & unpalatable
to swallow. Wild cherry bark has been reportedly used to brew a stimulating
tea, but the potential for cyanide poisoning makes it a risky beverage. In
very small doses, the human digestive tract is capable of breaking down plant
cyanides into harmless compounds. Accidental ingestion of a single
apple seed or cherry pit, therefore, though not recommended, is unlikely
to cause any serious trouble. However, larger doses cause anxiety,
confusion, dizziness, headaches & vomiting. In severe poisoning,
breathing difficulty; increased blood pressure and heart rate; and kidney
failure are follwed by coma & convulsions. Death may then occur
rapidly from respiratory arrest.
Autumn Crocus (Colchicum
autumnale) - There is an old legend telling about a mystical land called
Colchis. It was where famous poisoners lived. In a secret garden, full of
poisonous plants and herbs, grew a magic plant, the favorite flower of the
most beautiful poisoner Medea. A thousand years later, Carl Linnaeus
named that plant after this wonderful place. Actually this plant is
widespread on the meadows and grasslands in Europe and the Middle East. The
autumn crocus looks like an ordinary crocus, only it has pink-violet blossoms
and up to 30 cm long leaves. It provoked interest even in ancient times
not only because it blooms in the autumn and its fruits appear in the spring,
in contrast to the other flowers. Four thousand years ago it was already
known to Egyptians, Indians, Greeks, and Arabians as a quite successful but,
unfortunately, dangerous means of treating gout and rheumatism.
All parts of the plant are deadly poisonous. The toxic effects appear slowly
and gradually within 3 to 6 hours. These are nausea, excessive vomiting and
bloody diarrhoea, abdominal pain, weak arrhythmic pulse, low body
temperature, shortage of breath and, eventually, death. The bulb of the plant
contains the alkaloid colchicin, which is still used in the treatment
of gout. It is also used in genetics because of its property to cause
polyploidia. Colchicin pre-treatment of seeds leads to numerous mutations
of plants and is used for selective purposes in agriculture. 
Azalea (Rhododendron
occidentale sp.) - Azalea, a bonsai favorite, is the common name for
the dwarf type Rhododendrons. Although a low toxicity plant it is best
to keep children and pets away. All Rhododendrons should be treated
as poisonous. All parts of the plant are poisonous and contain
Andromedotoxin and arbutin glucoside - which causes Nausea, salivation, vomiting,
weakness, dizziness, difficulty in breathing and loss of balance.
100 to 225 grams of azalea leaves must be eaten to seriously poison a 55
lb (25 kg) child.
Calla Lily (Zantedeschia aethiopica). Smooth-edged arrowhead-shaped leaves which grow on long stalks. Flower may be white or green. Toxic Part: Leaves are injurious. When ingested, causes intense burning of the lips and mouth. Also direct irritant dermatitis.
Castor oil plant (Ricinus
communis) Castor bean fruit has been found in ancient Egyptian sarcophagi
among the objects that should accompany the dead in their voyage through
the Land of Death. The castor oil plant has large palm-shaped leaves with
7-9 portions, cluster-like blossoms and prickly fruits, each carrying 3 seeds.
All parts are poisonous, especially the beans. Castor beans affect
all animals and humans. Even one of them may be sufficient to cause
death. They contain some of the strongest toxins of our planet’s flora: the
alkaloid ricinin and the toxalbumin ricin, the latter being a plant
lectin, or protein, more toxic even than strychnos and cyanides. What is
more, it has the ability to accumulate in the organism until the lethal dose
is reached. The symptoms then are nausea and vomiting, stomach ache, bloody
diarrhoea, headache, cold sweat, sleepiness, disorientation, fever, shortage
of breath, seizures, followed by a collapse and death. It is also cultivated
in many other countries as an ornamental annual plant 1-2 m high. In the
U.S.A., it also grows in waste areas and roadsides. 50-70% of
its seed content is thick fatty oil, which contains vitamins A and D–the
so-called castor oil. It has been used as a purgative in medicine since ancient
times. 
Daffodil, Narcissus
(Narcissus pseudonarcissus). Many peple do not even suspect
that this seemingly innocuous plant actually contains poisonous alkaloids!
According to ancient Greek mythology, once there was a handsome slender
lad called Narcissus. Many beautiful nymphs were in love with him but he
was haughty and rejected their love. One day, he saw his face in the clear
water of a mountain brook and fell so deeply in love with his own reflection
that he couldn’t leave that place any more. He died there and a beautiful
flower –“the flower of death”– grew from the place where his head had dropped.
Consequently, it was named after the self-enamored Narcissus. The number
of the varieties has already exceeded 12,000. Most people are familiar
only with the aesthetic value of the daffodil and are completely unaware
of the fact that these wonderful blossoms – yellow or white with a red brim
– and the bulbs contain the poisonous alkaloids narcitine and narcicysteine.
They have no application in modern medicine.
DATURA (Datura ssp)
Coarse weedy herbs with stout stems and foul-smelling herbage. Leaves
are large and oval with wavy margins. Flowers are fragrant, white,
large, tubular, and showy. Toxic Part: All parts, particularly
the seeds and leaves. Symptoms: On ingestion: dry mouth, thirst,
redness of skin, disturbed vision, pupil dilation, nausea, vomiting, headache,
hallucination, excitement, rapid pulse, delirium, incoherent speech, apparent
insanity, convulsions, elevated temperature, high blood pressure, and coma.
In severe cases, death may result. On the other hand, natives in Brazil
smoke the leaves for the strong narcotic affect that is said to relieve asthma.
Delphinium (Delphinium spp.) Common Name: Delphiniums and Larkspurs. Tall or short herbs with usually blue showy flowers. Seeds are enclosed in a 3-celled capsule. Toxic Part: Entire plant. Symptoms: Burning sensation of the mouth and skin, nervousness, headache, weakness, prickling of the skin, low blood pressure, nausea, vomiting, depression, weak pulse, and convulsions. If eaten in large quantities, death may occur in less than 6 hours. Primary Poisons: alkaloids delphinine, ajacine and others.
Dieffenbachia (Dieffenbachia
sp.) - common name Dumbcane. The distinctive leaf pattern of the very
popular Dieffenbachia sp. is seen in many homes. All Parts of the plant
contain non soluble crystals that cause irritation and swelling of the mouth
and tongue which can result in death through asphyxiation. Painful and immediate
swelling of the mouth and throat occurs after chewing on dumbcane. Speech
impediment can occur, sometimes lasting for several days. This
plant however, is useful for purifying our indoor air.
Foxglove (Digitalis purpurea):
These familiar biennial plants are members of the Snapdragon Family native
to southern Europe and Asia, but highly prized in North American gardens
for their tall spikes of beautiful, bell-like flowers, in pink, blue, or
mauve, with dark spots inside the lip. Foxgloves are the pharmaceutical
source of the heart drug digitalis, which is poisonous in overdose. The plants
are also helpful in preserving other species of cut flowers with which they
may be arranged in a vase, or in stimulating the growth & endurance of
garden root vegetables, especially potatoes, with which they may be planted.
Poison is located in the sap, flowers, seeds, and leaves of Foxgloves, but
the greatest concentration of the toxin occurs in the leaves, even dried
ones. Poison type: Digitoxin, a glycoside which stimulates the heart.
A carefully prescribed dose often has miraculous effects on people
with heart conditions, but an overdoes may be fatal. Poisoning can occur
accidentally from consumption of the leaves or flowers by livestock,
or children who are attracted by the showy flowers, or the nectar, both of
which contain the glycoside poison. The sugar in the glycoside breaks down
during digestion, releasing the active chemical. Adults are occasionally
poisoned by the misuse of herbal preparations- tea from dried Foxglove leaves
is traditionally a diuretic- or by overdoses of prescribed digitalis. Another
possible cause of is misidentification. The leaves of Foxgloves
are easily mistaken for those of Comfrey, which are traditionally brewed
for tea; both share the same general form and a coasely hairy surface. Additional
confusion occurs because, in its first year, Foxgloves produce only leaves,
no flowers. Foxglove leaves, however, have finely toothed edges, whereas
Comfrey leaves are smooth. Digitoxin is dangerous, so Foxgloves must
be treated with caution. Symptoms of poisoning are increased heart
rate, leading to heart failure in the case of overdose. Other symptoms include
stomach upset, mental confusion, and convulsions. 
Horse Chestnut is a
familiar hardwood tree, well-known for its large compound leaves and colourful
fruit in their spiky cases. Though this fruit is similar to the edible, Sweet
Chestnut, the two trees are unrelated. Horse Chestnut is toxic. Children
are especially attracted by the luster of Horse Chestnuts, which are
traditionally strung and struck against one another in the game of "conkers."
All parts of Horse Chestnut contain toxins, especially the fruit. The
toxin is Aesculin, a bitter, poisonous glycoside which breaks down blood
proteins. This property has led to the development of the common rat
poison, warfarin, extracted from clovers, which contain a similar toxin.
Most poisonings occur from people roasting & eating the fruit in the
mistaken belief that they are the same as Sweet Chesnuts; they aren't! Some
people claim you can boil the toxins out of Horse Chestnuts then dry them
& grind them into a coarse flour, but you'd have to be pretty desperate,
and is not recommended. There is no risk in handling the tree or its
fruit. Chesnut poisoning is rarely fatal, but typically causes vomiting,
loss of coordination, stupor and occasionally paralysis.
Iris (Iris Ssp.) Lily-like with leaves which are long and narrow. Flowers are large with pink, blue, lilac, and purple to white, brown, yellow, orange and almost black flowers. Toxic Part: Leaves and rootstock. Burning and severe pain in the intestinal tract; nausea and severe diarrhoea. Skin irritation may result from the sap and seeds in some species. Primary Poisons: irisin, iridin or irisine .
Laburnum: (Laburnum anagyroides)
Other names for Laburnum include Golden Chain Tree and Golden Rain Tree.
The yellow flowers of early summer produce the pods and pea-like fruit which
are highly toxic. Symptoms may include Abdominal pain, elevated temperature,
tremors, unsteady gate and convulsions. Fatal poisoning in horses has been
reported, mostly involving high consumption of seeds and pods eaten from
trees to which they had been tied. Even the roots contain a poisonous alkaloid.
The bark and seeds do more damage than the leaves. 
Lily of The Valley (Convallaria
majalis) - This is one of the most beautiful flowers that appear in
wet forests in Europe, Asia, and North America from April till June.
Every part of the plant is poisonous because it contains about 20
poisonous glycosides such as convalatoxin, convalarin, and convalamarin,
as well as saponins. They cause poisoning characterized by strong headache,
nausea and vomiting, slow pulse and excessive urination. The victims are
often domesticated animals because the may lily is a widely distributed cultivated
plant. 
Oleander (Nerium oleander) The poisonous effect of the oleander has been well known for centuries. There are data relating to its having poisoned Napoleon soldiers during one of their campaigns. The oleander contains the toxic glycoside oleandrin. The latter can be considered a cardiac glycoside and is very similar to those found in •foxglove• (Digitalis) and •pheasant's eye• (Adonis vernalis). The characteristic poisoning symptoms are nausea, vomiting, accelerated or retarded heartbeat and cardiac arrest.
Peony (Paeonia peregrina) According to the
famous Roman writer and scholar Gaius Plinius Secundus (23-79BC), peony is
the oldest cultivated flower. It has beautiful blossoms, reaching 13 cm in
diameter and colored in all shades of red in its natural state. People in
the past were very fond of it and much charmed by its beauty. The plant is
cultivated in many countries throughout the world and still grows naturally
in South and Southeast Europe as well as in Southwest Asia to a height of
60-70 cm. Peony is a herb but all parts of the plant, when taken in
high doses, are poisonous and cause vomiting, paresthesias, accelerated heartbeat.
It is proved that a small dose provokes excessive menstrual bleeding, which
leads to abortion and, at the same time, makes the clotting of blood easier.
The substances extracted from the roots and the seeds have no application
in medicine. 
Potato
(Solanum tuberosum). Once upon a time, someone brought
to Europe a plant which had been cultivated by South American Indians for
centuries before the European expansion to the West. It was
about 60-80 cm high; had white, pink or violet blossoms; and generated in
its subterranean part up to 50-60 tubers whose weight varied from 2-3 g to
2-3 kg. The one who brought it surely didn’t have the slightest idea
of its forthcoming expansion across fields in Europe and, subsequently the
whole world. This plant was the potato, which contains the poisonous
glycoalkaloid solanine in all its parts but mostly in the blossoms and in
the fruit. Its content is extremely high when tubers are unripe or green
as a result of incorrect storage but they cannot cause poisoning because
solanin decomposes when boiled. Only the fruit, blossoms, seeds,
sprouts, and sun-greened tubers may be dangerous. They can bring about
stomach ache, nausea and vomiting, dizziness, psychic depression, breathing
disruptions, irregular pulse and even coma in the case of high dose intake
and lack of therapy.
Pyrethrum (Tanacetum (Chrysanthemum) cinerariifolium) - Pyrethrum is a perennial plant which has been commercialised and many variants, and colours, are now available for the gardener. The concentration of the active constituents, pyrethrins, increase at higher altitude, and flower production decreases with shade. Pyrethrins are produced in the flowers and are commonly used as insecticides. These compounds work directly on the nervous systems of aphids, mites, leafhoppers, and other insects without harming fish, waterfowl, plants or mammals. Symptoms include Headaches, gastroenteritis, dizziness and psychotic changes.
Wisteria (Wisteria Ssp.) - -poisonous Parts: all, flowers, seeds, leaves Primary Poisons: wistarine seeds, pods and entire plant. digestive upset caused by alkaloid toxins. Nausea, repeated vomiting, stomach pains, severe diarrhoea, dehydration and collapse
Yew (Taxus baccata).
Yew is highly valued in furniture industry for its hard reddish timber resistant
to the damage of insects and fungi. Yew is an evergreen tree, up to
32m high. Its treetop is thick and oval, its leaves are dark green
and shiny above; beneath they are matt and milky green. The plant grows very
slowly; therefore, it can reach an age of about 4000 years. Yew is also cultivated
as a decorative plant in many countries. In fact, all parts of the
plant are poisonous which is due mostly to the alkaloid taxin. Symptoms
include nausea and vomiting, increased salivation, stomach ache, diarrhoea,
sleepiness, shortage of breath, trembling, spasms, malfunction of the cardiovascular
system which leads to collapse and death. The bark of the Yew
is used to produce Taxol, used in the treatment of certain cancers.