Who were they named after?

Magnolias were named after Pierre Magnol.

 

Buddleja davidii, after two priests Rev Buddle and Pere David.
Bougainvillea after Admiral Bougainville.

 

But why did they change the spelling of buddleja?

 

I really don't no, though a lot of people use buddleia.

 

Lilium henryi after Ernest Henry Wilson also Clematis henryi and Lonicera henryi.
Lilium davidi after Pere David.
Douglas fir (Pseudotsuga menziesii) after David Douglas and Archibald Menzies.
Lilium mackliniea after the partner of Frank Kingdom Ward.

 

Note a lot of plants are named after dead white people, generally male.

 

The forsythia plant is named after William Forsyth, the great-great-grandfather of entertainer Bruce Forsyth

 

Viburnum forrestii after George Forrest. He also has an Abies, a Pieris, a Hedychium, a Sorbus, an Acer and a Buddleja plus quite a few others.
By the way @LouisFerdinand do you grow any of these?

 

Berberis darwinii, discovered during his journey on the Beagle in 1835.

 

The Romans didn't have J either so Julius Caesar would have been Iulius Caesar.

 

I read a very good book about plant hunters this year. Can't remember what it was called now, but most of them were white male and had plants named after them.
An exception- Miss Willmott's Ghost.

 

Genus Fuchsia named after botanist Leonhart Fuchs.
Fuchsia hatschbachii after Gert Hatschbach.
Lophora williamsii
Leuchtenbergia principis after Maximillian Eugen Joseph Duke of Leuchtenberg.
Strelitzia reginae after Charlotte of Mecklenburg-Strelitz Queen of George III of Great Britain and England.

 

Ah but Miss Will Mott's Ghost was apparently named because she used to scatter seed of the eryngium in gardens she visited - leaving a ghost ie new plants

 

Drimys winterii named after Captain Wynters, second in command on Drake's voyage around the world, who discovered that its leaves/bark cured scurvy on board his ship.

From Wikipedia: When Sir Francis Drake sailed round the world in 1577-80, of the four ships accompanying the Golden Hind at the outset, the only ship that successfully reached the entrance to the Strait of Magellan was the Elizabeth, captained by John Wynter. Before entering the Strait, in July 1578, Drake sent Wynter ashore where he learned indigenous people ate the astringent bark.[8] The Elizabeth transversed the Strait. A week later the two ships were separated in a storm and Wynter turned back. Wynter returned in 1580[9] with a supply of Drimys bark, and for centuries before vitamin C was isolated, "Winter's Bark" was esteemed as a preventive and remedy for scurvy— correctly so, for an infusion of D. winteri sustained Captain James Cook and his crew in the South Pacific, and the naturalist accompanying his voyage of exploration, Johann Reinhold Forster, was the first to officially describe and name D. winteri.[10]