Dahl was a Swedish botanist and a student of pioneering taxonomist Carolus Linnaeus. After studying at the Uppsala University and the University of Kiel, Germany, he taught medicine and botany at the University of Helsinki, Finland. Dahl was a renowned botanist and publisher of Observationes botanicæ circa Systema vegetabilium divi a Linné.

The genus, Dahlia, is named after him although it is not clear exactly who made that choice.

French Father David, was sent to China as a missionary. He was a man of wide interests beyond his religion including botany, zoology, geology and ornithology.

While attending to his priestly duties, he also had time to collect and record about 250 new plant species including Davidia involucrata, Rodgersia aesculifolia, Photonia davidiana, Acer davidii, Rosa davidii, Astilbe chinensis var. davidii, Buddleja davidii, Chrysosplenum davidianum, Clematis armandii, Lilium davidii, Pinus armandii, Populus tremuloides var. davidiana.

From Seattle, Washington, Mr. Davidson was an author, gardener and botanist. His books include Lewisias and Portfolio: Oregon Iris Trek. Plants named in his honor include  Pulmonaria 'Roy Davidson'.

*Email comment from David: "Penstemon davidsonii was named in 1892 for George Davidson (1825-1911), not for B. Leroy Davidson."

A German physician, Dieffenbach was also a geologist and naturalist. He was one of the first to explore much of New Zealand and published a book titled, Travels in New Zealand in 1843. The genus, Dieffenbachia (Dumbcane), was named for him.

Irish plantswoman and garden writer known for her garden in Dublin. She has lectured and collected plants in several countries and is a regular on gardening television and in the news papers. Her books include Garden Artistry and Helen Dillon on Gardening.

Plants named in her honor include Heuchera 'Helen Dillion' and Scabiosa 'Helen Dillon'.

Pedanius Dioscorides was a Greek physician, pharmacologist, botanist, and author of De Materia Medica which was a 5-volume encyclopedia about herbal medicine and related medicinal substances, that was widely read for more than 1,500 years.

David Douglas from the village of Scone in Scotland was one of the best known plant explorers of the early to mid 19th century. His explorations of the North American continent along with others such as Pennsylvanian, John Bartram, the Swedish botanist, Peter Kalm and Englishman, Thomas Nuttall opened that part of the world to European gardeners.

In his youth, Douglas moved to Glasgow and became associated with the renowned Professor of Botany, William James Hooker of Glasgow University and later, the Royal Botanic Garden at Kew. Through this connection, Douglas became a plant collector for the Royal Horticultural Society (then the Horticultural Society of London) who sponsored his trips to America.

Douglas was known for his adventurous manner which, ironically, eventually led to his death in Hawaii. Perhaps tops on his list of discoveries was the tree that bears his name, the Douglas Fir (Pseudotsuga menziesii) which he found in the Cascade Mountain range of the Western part of North America. He named the plant for its resemblance to hemlock (which is in the genus, Tsuga, therefore Pseudtsuga) and for fellow Scottish explorer, Archibald Menzies. Menzies was actually the first to describe the species but Douglas was first to send seeds back to England.

During his career as a plant explorer, he made three trips to North America where he visited both the east and west coast. However, he seemed to be most attracted to the Northwest Territory and its mountainous regions. He was sponsored by various individuals and organizations and sent both live plants and preserved specimens back to London.

In 1834 after having a falling out with the Royal Horticultural Society and losing his funding, Douglas left North America but first made his way to the Hawaiian Islands. He spent several months exploring for plants there but, at least according to reports, he stumbled into a deep pit which was constructed to capture wild cattle on the island. They discovered his mangled, dead body and concluded that a wild bull also in the pit must have gorged him to death. Some people theorize that he was murdered but this was never proven.

Of course, local peoples were already familiar with their native plants, but Douglas "discovered" many species meaning that he found specimens unknown in Europe and sent them back to his sponsors. Among the more well-known plants he introduced include Oregon grape holly (Mahonia aquifolium), Western hemlock (Tsuga heterophylla), Balsam Fir (Abies balsamea), Yellow Fritillary or Mission Bell (Fritillaria pudica), Western White Pine (Pinus monticola), Ponderosa Pine (Pinus ponderosa), and the Sitka Spruce (Picea sitchensis).

Plants including Iris douglasiana, Limnanthes douglasii, Allium douglasii,  Phlox douglasii, Douglasia nivalis (mountain pink), Acer glabrum var. douglasii (Douglas’s maple), Cicuta douglasii (water-hemlock), Juniperus horizontalis 'Douglasii' and Polygonum douglasii (Douglas’s knot-weed) are named for him.

English pharmacist who was Mayor of Oxford, England in 1900. He collected about 200,000 plant specimens from the British Isles for the Oxford University Herbarium.

The species, Geranium x oxonianum ‘Claridge Druce’ is named for him.

Born in Scotland, Drummond worked as the curator of the Botanic Garden at Cork, Ireland. In 1829, he was appointed to develop a botanic garden in Western Australia. During his time in Australia, he explored the continent for plants to send back to England.

He is credited with introducing several plant species including Chorizema varium, Pimelia spectabilis and Leschenaultia biloba.

The species, Acacia drummondi was named after him and the genus Drummondita for both him and his brother Thomas Drummond.

French architect who specialized in restoration of classical French gardens such as the châteaux of Vaux-le-Vicomte, Courances and Corbeil Cerf in France and Schlosspark Nordkirchen in Germany. He was associated with the pools and Mermaid Fountain at Blenheim Palace in Oxfordshire, England.