Variation
Allium cepa var. aggregatum
Aggregatum Group
This group includes shallots (potato onions, scallions).

Shallots 
Previous species name is Allium ascalonicum
Shallots are thought to originate in the Central or South-east Asia and now widely found from India to the eastern Mediterranean and have been cultivated for hundreds of years. 

They are biannual but are commonly grown as an annual for their bulbs. Shallots are commonly referred to the vegetable with edible green leaves and stems (spring onions) but these non-bulbing onions are not true shallots but are a variety of Allium cepa var. cepa.

This true shallots and its varieties grow from 300 mm (1 ft) to 1 m (3 ft) tall by 300 mm (1 ft) wide and a differ from onions by producing an aggregate cluster of several papery coated bulbs that are composed of multiple cloves. They varying colour from golden brown to rose red with off white flesh that may be tinged green or magenta. 

They have edible pale to mid green hollow basal leaves and produced a globular cluster (umbel) of a greenish white star-shaped flowers (stellate) high above the foliage on a tall scape during summer in their second year of growth. 

Under cultivation shallots prefer a cool mild to sub tropical winter and grow in an open sunny position but will tolerate some shade. They are planted a prepared deep well-drained organic rich moist clay loam that is the neutral tending acidic with a pH range from 6.5 to 7.5. They dislike fresh manure in the soil as it is too high in nitrogen and will reduce the keeping quality of the bulbs and acidic soils below pH 5.5 may require liming. 

They requiring a long growing season and can be planted during autumn and harvested in early summer of or planted in cooler regions during early spring and harvested during late summer when the leaves decline and become yellow. 

When planting out space the bulbs 150 mm (6 in) apart and 50 mm (2 in) deep with the pointy end up at soil level. Once harvested the bulbs should be dried in a shady well ventilated place for a week then they will store well for months.
There are many varieties some examples are;

'Atlantic'
This variety produces large bulbs that are crisp and tasty and stores will once harvested.

'Drittler White Nest'
This older variety produces variable size of bulbs that are crisp and tasty.

'Giant Yellow Improved'
This variety produces high yields of bulbs with yellow brown skin that a consistently large.

'Sante'
This variety produces high yields of large round brown skinned bulbs with pinkish white flesh and stores well.  This plant tends to go to seed (bolt) and should be planted from mid to late spring.

Onion Types
Short Day
Onions that require a short amount of daylight hours (10 - 12) are planted from late summer to autumn and are harvested during spring.  They produced bulbs (onions) that are normally sweet but do not store well.  In Australia they are commonly grown in the warmer regions of Queensland and New South Wales.

Long Day
Onions that require a long amount of daylight hours (14 - 16) are planted during early spring and are harvested during autumn. These varieties are best suited to cold regions (sub Arctic) where the day length is very long and produced pungent onions that store well.  This type of onion is not relevant to Australia where Short day and intermediate types are grown.

Intermediate
Onion varieties in this group require 13 to 14 hours of daylight per day and are planted from winter to early spring and harvested from mid to late summer. They are commonly grown in cooler regions and store moderately well.  In Australia they are grown in the southern states.

Opened Pollinated
These traditional varieties produce offspring that are similar to the mother and have been selected for their desirable traits.  Care must be taken when collecting seed that cross pollination with other varieties has not occurred and to maintain the integrity careful selection of the bulbs is required for each generation.

Hybrids
Hybrid plants are the result of crossing two parent lines and produce varieties that have a high yield and a greater disease resistance than opened pollinated varieties. The seeds that are produced cannot be re-sowen as they will not be true to type and fresh set must be obtained from the seed companies each year.

Varieties
Brown Onions
These onions have a brown to pale yellowish skin with creamy coloured flesh and a strong flavour. They are commonly used in cooking. Examples of the varieties are;

'Creamgold'
This variety is an opened pollinated intermediate type and is planted from autumn to winter then harvested from midsummer to autumn. In Australia it is grown in New South Wales, South Australia, Tasmania, Western Australia and Victoria.

'Murray Brown'
This long and day opened pollinated variety is planted from late winter to early spring and is harvested from late summer to autumn. It is commonly cultivated in South Australia.

Red Onion
These varieties are commonly misnamed Spanish onions and have a purplish red skinned with white flesh that may be tinged red.  They are available in medium to large sized with a mild to sweet flavour that becomes a more pungent after being stored for 3-4 months. They are commonly eaten raw or grilled and can be lightly cooked with other foods.  They are also used in salads adding colour and flavour. Examples of the varieties are;

'Redshine'
This open pollinated intermediate day variety is planted during early winter that is harvested from early to mid summer.  In Australia it is grown in New South Wales, South Australia, Western Australia, Victoria and Tasmania.

'Redwing'
This intermediate day hybrid variety is planted during early spring and harvested from late summer to autumn. In Australia it is grown in Victoria, South Australia and Western Australia.

'Red Emperor'
This intermediate day hybrid variety can be planted during late autumn and harvested during early summer all may be planted in cooler regions during late winter and harvested during mid-summer.  In Australia it is grown in New South Wales and Tasmania.

White onion
White onions have a flavour that is almost as strong as brown onions and are very variable in size and skin characteristics. Examples of the varieties are;

'Bianca'
This hybrid intermediate day variety is planted from autumn to winter and is harvested during mid-summer. In Australia it is grown in New South Wales, South Australia, Western Australia and Victoria.

'Gladalan White'
This open pollinated short day variety is planted during early winter and harvested from early to midsummer. In Australia it is grown in Queensland, New South Wales, South Australia, Western Australia and Northern and Victoria.

'White Spanish'
This open pollinated long day variety is planted during late winter and harvested in late summer. In Australia it is grown in South Australia.

'Mild Onions'
Varieties under this heading at a low pungency but retain their lingering sweet taste. They are commonly eaten raw in sandwiches or salads and have no burning aftertaste or bring tears to your eyes.