Magnolia grandiflora, commonly known as the Southern magnolia or bull bay, is a magnolia native to the southeastern United States, from coastal Virginia south to central Florida, and west to East Texas. It is a medium to large tree 20-30 m tall with a striking appearance, both in leaf and in bloom.

The leaves are evergreen, simple and broadly ovate, 12-20 cm long and 6-12 cm broad, with smooth margins. They are dark green, stiff and leathery, and often scurfy underneath with yellow-brown pubescence. They will bronze, blotch, and burn in severe winters at the northern limits of cultivation, but most still cling until they are replaced by new foliage in the spring. In climates where the ground freezes, winter sun appears to do more damage than the cold itself. In the northern hemisphere the south side of the tree will experience more leaf damage than the north side of the tree. Two extremes are known, with leaves white underneath and with leaves brown underneath. The brown varieties are claimed to be more cold-hardy than the white varieties, but this does not appear to be proven as yet.

The large, showy, citronella-scented flowers are white, up to 30 cm across and fragrant, with 6-12 petals with a waxy texture, emerging from the tips of twigs on mature trees in late spring.

Cultivation and uses

Southern magnolia is a very popular ornamental tree throughout the southeastern United States, grown for its attractive foliage and flowers. On the east coast of the United States, cold-hardy cultivars have been seen planted up to and even north of the Ohio River, where large tree specimens become increasingly more rare and eventually are only found as shrubs before disappearing altogether from the landscape; for example, large mature trees are common in the Cincinnati, Ohio area but begin to taper off in size and occurrence until they are generally absent altogether in Columbus, Ohio. This "subtropical indicator" tree is seen in some gardens as far north as southern Connecticut; farther north it is extremely difficult to cultivate. Towards the northern limit of its cultivation, it may suffer dieback from very hard freezes, but weathers normal freezes well. On the west coast it is commonplace as far north as Vancouver, British Columbia.

As newer cultivars have been found to be more cold hardy, the cultivated range has continued to spread farther north with some being planted around Chicago. 'Bracken's Brown Beauty', 'Edith Bogue' and '24 Below' are some of the most cold hardy varieties.

A dwarf cultivar called: Magnolia 'Little Gem' is now available.

The southern magnolia is the state tree of Mississippi, and the state flower of Mississippi and Louisiana.