Photo of olives.

List of Plants that start with O

The most well-known plants and fungi, listed by their common names.

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Oak tree

Scientific name: quercus robur

Oaks are a group of trees and shrubs from the Northern hemisphere. There are both deciduous and evergreen oaks. Most people are familiar with the common oak trees that grow acorns.
Oak wood is used for making furniture, and was once used for making houses. It is still used for making wine barrels.

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Oats

Scientific name: avena sativa

Oats are a cereal crop grown mainly for turning into rolled oats and oatmeal for making porridge. It is also used as animal feed, particularly for horses.

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Oleander

Photo of oleander flowers.
Photo by The Equinest
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Scientific name: nerium oleander

Oleanders, also known as rose laurel, are a pretty, evergreen flowering shrub. They usually have pink or white flowers.
Oleanders are one of the most poisonous plants known. Their sap is toxic, and even the dead, dried plant is dangerous. Horses have been known to die from eating oleander leaves. Even a single leaf might be enough to kill a small child.

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Olive

Photo of olives
Photo by Simon and You
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Scientific name: olea europaea

Olives are the fruit of a small, slow-growing tree. They are originally from the Mediterranean region and grow best in poor soils in Mediterranean climates. Olives can be grown easily from both seeds and cuttings, but trees grown from seed don't always grow good fruit.
Olives can't be eaten fresh from the tree, they are too bitter. Olives need to be prepared by soaking them in salty water or otherwise preparing them to be eaten. Some types of olive can be pressed and oil made from them.

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Onion

Scientific name: allium cepa

Onions are a vegetable. There are many different kinds of onions, ranging in size and colour from purple to red to white to green.
Onions are used in almost every kind of food, raw or cooked. They can be very sharp when they are raw and many children do not like raw onions, but when they are cooked they are quite sweet.

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Orange

Photo of orange fruit
Photo by Kyle McDonald
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Scientific name: citrus sinensis

An orange is the name for both a colour and a citrus fruit. Oranges are similar to lemons but are very sweet and can be eaten raw, squeezed to make juice, and can be made into marmalade. The colour orange can be made by mixing red and yellow paint.

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Orchid

Photo of orchid flowers
Photo by Louise Docker
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Scientific name: family: orchidaceae

Orchids are a very big plant family. There are more different kinds of orchid than there are different kinds of bird. Orchids are found everywhere except deserts and glaciers. Orchids are grown for their pretty flowers. You can tell an orchid mainly by one of its petals being somehow different to all the others.

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Oregano

Photo of oregano
Photo by Sonja Pieper
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Scientific name: origanum vulgare

Oragano is a herb often used in Greek, Spanish and Italian cooking. It comes from the Mediterranean region. Oregano is very commonly used on pizza.