There are 163 trees that start with the letter O, from Oahu Alectryon to Ozark Witch Hazel. Below you will find them listed alphabetically along with some general information about each. Click the toggle view buttons in the top right corner to switch between the card and the table view.
For each item you will find the following information
Order: The subclass the trees belongs to
Habitat: The places or type of weather the trees lives in
Scientific name: The designation that scientists use to catalog the species
Name: Oahu Alectryon
Order: Sapindales
Habitat: Native to Hawaii
Scientific name: Alectryon macrococcus
Name: Oak
Order: Fagales
Habitat: Temperate forests
Scientific name: Quercus
Name: Oak Leaf Hydrangea
Order: Ericales
Habitat: Native to southeastern United States, often found in moist, well-drained soils in forests and along stream banks.
Scientific name: Hydrangea quercifolia
Name: Oaks and Pine
Order: Fagales
Habitat: Temperate forests
Scientific name: Quercus spp.
Name: Oaxacan Rosewood
Order: Fabales
Habitat: Central America
Scientific name: Dalbergia congestiflora
Name: Oban Pine
Order: Pinales
Habitat: Mexico
Scientific name: Pinus oaxacana
Name: Oblique-leaved Alangium
Order: Cornales
Habitat: Southeast Asia
Scientific name: Alangium obliquum
Name: Oblong Aralia
Order: Apiales
Habitat: East Asia
Scientific name: Aralia cordata
Name: Oblong Burr Oak
Order: Fagales
Habitat: Central United States
Scientific name: Quercus macrocarpa var. oliviformis
Name: Oblong-leaved Yellowwood
Order: Proteales
Habitat: Southern Africa
Scientific name: Podocarpus latifolius
Name: Ocania Myrtle
Order: Myrtales
Habitat: Peru
Scientific name: Eugenia ocaina
Name: Ocaña Oak
Order: Fagales
Habitat: Colombia
Scientific name: Quercus ocaneana
Name: Occidental Plane Tree
Order: Proteales
Habitat: Native to eastern North America
Scientific name: Platanus occidentalis
Name: Ochna
Order: Malpighiales
Habitat: Tropical Africa and Asia
Scientific name: Ochna spp.
Name: Ochrocarpos
Order: Malpighiales
Habitat: Africa
Scientific name: Ochrocarpos africanus
Name: Ochroma Pyramidale
Order: Malvales
Habitat: Central and South America
Scientific name: Ochroma pyramidale
Name: Ocoee Silverbell
Order: Ericales
Habitat: Southeastern United States
Scientific name: Halesia tetraptera var. monticola
Name: Ocotea
Order: Laurales
Habitat: Central and South America
Scientific name: Ocotea spp.
Name: Ocotea Cernua
Order: Laurales
Habitat: South America
Scientific name: Ocotea cernua
Name: Ocotea Cymbarum
Order: Laurales
Habitat: South America
Scientific name: Ocotea cymbarum
Name: Ocotea Foetens
Order: Laurales
Habitat: Canary Islands
Scientific name: Ocotea foetens
Name: Ocotea Martinicensis
Order: Laurales
Habitat: Lesser Antilles
Scientific name: Ocotea martinicensis
Name: Ocotea Oblonga
Order: Laurales
Habitat: Central America
Scientific name: Ocotea oblonga
Name: Ocotea Rubra
Order: Laurales
Habitat: South America
Scientific name: Ocotea rubra
Name: Ocotea Viridiflora
Order: Laurales
Habitat: South America
Scientific name: Ocotea viridiflora
Name: Ocotillo
Order: Caryophyllales
Habitat: Southwestern United States and Mexico
Scientific name: Fouquieria splendens
Name: Ocuba Palm
Order: Arecales
Habitat: South America
Scientific name: Oenocarpus bataua
Name: Odina Woodier
Order: Sapindales
Habitat: Asia
Scientific name: Lannea coromandelica
Name: Odoardo's Crab Apple
Order: Rosales
Habitat: China
Scientific name: Malus odoardi
Name: Odontadenia Macrantha
Order: Gentianales
Habitat: South America
Scientific name: Odontadenia macrantha
Name: Odontoglossum
Order: Asparagales
Habitat: Tropical America
Scientific name: Odontoglossum spp.
Name: Oecus
Order: Sapindales
Habitat: Southeast Asia
Scientific name: Oecus dipsaceus
Name: Oenocarpus Bacaba
Order: Arecales
Habitat: South America
Scientific name: Oenocarpus bacaba
Name: Oenocarpus Bataua
Order: Arecales
Habitat: South America
Scientific name: Oenocarpus bataua
Name: Oenocarpus Distichus
Order: Arecales
Habitat: South America
Scientific name: Oenocarpus distichus
Name: Offa Palm
Order: Arecales
Habitat: Brazil
Scientific name: Syagrus coronata
Name: Officier Tree
Order: Myrtales
Habitat: Australia
Scientific name: Xanthostemon chrysanthus
Name: Ogeechee Lime
Order: Malvales
Habitat: Southeastern United States
Scientific name: Nyssa ogeche
Name: Ogeechee Tupelo
Order: Ericales
Habitat: Southeastern United States
Scientific name: Nyssa ogeche
Name: Ogham Tree
Order: Coniferales
Habitat: Europe and Asia
Scientific name: Juniperus communis
Name: Ogier Nut
Order: Malpighiales
Habitat: Brazil
Scientific name: Couepia longipendula
Name: Ogonori
Order: Caryophyllales
Habitat: Western North America
Scientific name: Sarcobatus vermiculatus
Name: Ohai
Order: Fabales
Habitat: Easter Island
Scientific name: Sophora toromiro
Name: Ohi'a Lehua
Order: Myrtales
Habitat: Hawaii
Scientific name: Metrosideros polymorpha
Name: Ohio Buckeye
Order: Sapindales
Habitat: Eastern United States
Scientific name: Aesculus glabra
Name: Ohio Pine
Order: Pinales
Habitat: Eastern United States
Scientific name: Pinus strobus
Name: Oho
Order: Pittosporales
Habitat: Southern Africa
Scientific name: Ptaeroxylon obliquum
Name: Oiao
Order: Proteales
Habitat: Philippines
Scientific name: Helicia obovatifolia
Name: Okame Cherry
Order: Rosales
Habitat: Ornamental cultivar
Scientific name: Prunus x incamp 'Okame'
Name: Okari Nut
Order: Proteales
Habitat: New Guinea
Scientific name: Terminalia kaernbachii
Name: Okina
Order: Apiales
Habitat: Caribbean
Scientific name: Dendropanax arboreus
Name: Oklahoma Redbud
Order: Fabales
Habitat: Central United States
Scientific name: Cercis canadensis var. texensis
Name: Okume
Order: Sapindales
Habitat: West Africa
Scientific name: Aucoumea klaineana
Name: Okuta Palm
Order: Arecales
Habitat: Indonesia
Scientific name: Livistona okmueensis
Name: Okwango Quinine Tree
Order: Gentianales
Habitat: Southern Africa
Scientific name: Rauvolfia caffra
Name: Olacaceae
Order: Santalales
Habitat: Tropical regions
Scientific name: Olacaceae
Name: Olallie Berry
Order: Rosales
Habitat: Native to western North America, often found in moist, shaded areas in forests and along streams.
Scientific name: Rubus ursinus
Name: Olax Scandens
Order: Olacales
Habitat: Southeast Asia
Scientific name: Olax scandens
Name: Old Alder
Order: Fagales
Habitat: Europe and West Asia
Scientific name: Alnus glutinosa
Name: Old Field Pine
Order: Pinales
Habitat: Southeastern United States
Scientific name: Pinus palustris
Name: Old Man Cactus
Order: Caryophyllales
Habitat: Mexico
Scientific name: Cephalocereus senilis
Name: Old Man Pine
Order: Pinales
Habitat: Western Himalayas
Scientific name: Pinus gerardiana
Name: Old World Ebony
Order: Rosales
Habitat: South Asia
Scientific name: Diospyros ebenum
Name: Oleander
Order: Gentianales
Habitat: Mediterranean region
Scientific name: Nerium oleander
Name: Oleaster
Order: Rosales
Habitat: Temperate regions of Europe and Asia
Scientific name: Elaeagnus angustifolia
Name: Oleerod
Order: Rosales
Habitat: Central America
Scientific name: Amyris oleifera
Name: Olive
Order: Lamiales
Habitat: Mediterranean climate regions
Scientific name: Olea europaea
Name: Olive Bark Tree
Order: Laurales
Habitat: Southeast Asia
Scientific name: Terminalia oliveri
Name: Olive Buckthorn
Order: Rosales
Habitat: Mediterranean region
Scientific name: Rhamnus oleoides
Name: Olive Daphne
Order: Laureales
Habitat: Asia
Scientific name: Daphniphyllum orientale
Name: Olive Hawthorn
Order: Rosales
Habitat: Eastern United States
Scientific name: Crataegus olivacea
Name: Olive Plum
Order: Rosales
Habitat: Cultivated
Scientific name: Prunus amygdalus
Name: Olive Tortoise Shell
Order: Rosales
Habitat: Cultivated
Scientific name: Blepharocaly x olea
Name: Oliver's Aspen
Order: Malpighiales
Habitat: Western United States
Scientific name: Populus tremuloides var. oliveri
Name: Olivo
Order: Laurales
Habitat: Mediterranean region
Scientific name: Olea europaea
Name: Olneya
Order: Fabales
Habitat: Southwestern United States and Mexico
Scientific name: Olneya tesota
Name: Olohua
Order: Proteales
Habitat: Philippines
Scientific name: Helicia obovatifolia
Name: Olong Tree
Order: Laurales
Habitat: Southeast Asia
Scientific name: Cryptocarya obovata
Name: Olympia Serviceberry
Order: Rosales
Habitat: Northwestern United States
Scientific name: Amelanchier alnifolia var. semiintegrifolia
Name: Oma Oma Nut
Order: Malpighiales
Habitat: Indonesia
Scientific name: Barringtonia procera
Name: Omalanthus Populifolius
Order: Malpighiales
Habitat: Australia
Scientific name: Homalanthus populneus
Name: Omanine
Order: Myrtales
Habitat: Sri Lanka
Scientific name: Syzygium caryophyllatum
Name: Omanite
Order: Pinales
Habitat: Middle East
Scientific name: Juniperus excelsa
Name: Omanite Pine
Order: Pinales
Habitat: Oman
Scientific name: Pinus omanensis
Name: Ombu
Order: Asterales
Habitat: South America
Scientific name: Phytolacca dioica
Name: Ombu Tree
Order: Caryophyllales
Habitat: South America
Scientific name: Phytolacca dioica
Name: Omoana
Order: Malvales
Habitat: West Africa
Scientific name: Mansonia altissima
Name: Omurana
Order: Laurales
Habitat: Hawaii
Scientific name: Cryptocarya omurana
Name: Oncoba Spinosa
Order: Malpighiales
Habitat: Africa
Scientific name: Oncoba spinosa
Name: Onderste Bosch
Order: Ericales
Habitat: South Africa
Scientific name: Blumea cylindrica
Name: Ondina
Order: Laurales
Habitat: Chile
Scientific name: Persea lingue
Name: One-Seed Juniper
Order: Pinales
Habitat: Southwestern United States
Scientific name: Juniperus monosperma
Name: Oneida Serviceberry
Order: Rosales
Habitat: Northeastern United States
Scientific name: Amelanchier interior
Name: Onion Cedar
Order: Cupressales
Habitat: Japan
Scientific name: Juniperus procumbens
Name: Onobrychis montana
Order: Fabales
Habitat: Europe
Scientific name: Onobrychis montana
Name: Onondaga Oak
Order: Fagales
Habitat: Eastern United States
Scientific name: Quercus prinoides
Name: Ontari Palm
Order: Arecales
Habitat: South America
Scientific name: Euterpe oleracea
Name: Ooah Tree
Order: Caryophyllales
Habitat: Central Africa
Scientific name: Tessmannia africana
Name: Oolampia
Order: Myrtales
Habitat: Australia
Scientific name: Syzygium oleosum
Name: Oolooman Ash
Order: Lamiales
Habitat: Mexico
Scientific name: Fraxinus uhdei
Name: Ooltewah Juniper
Order: Pinales
Habitat: Southeastern United States
Scientific name: Juniperus x ashei
Name: Ootanga
Order: Apiales
Habitat: Coastal regions of northern Europe
Scientific name: Ligusticum scoticum
Name: Opah
Order: Proteales
Habitat: Philippines
Scientific name: Helicia philippinensis
Name: Opalo
Order: Sapindales
Habitat: South America
Scientific name: Jessenia bataua
Name: Opangi Nut
Order: Malvales
Habitat: Central America
Scientific name: Pachira aquatica
Name: Opangia
Order: Malvales
Habitat: Central America
Scientific name: Pachira aquatica
Name: Opauca
Order: Laurales
Habitat: Brazil
Scientific name: Ocotea opaca
Name: Opham
Order: Fagales
Habitat: Middle East
Scientific name: Quercus libani
Name: Opichti
Order: Pinales
Habitat: Central America
Scientific name: Pinus oocarpa
Name: Opium Poppy
Order: Ranunculales
Habitat: Native to the Mediterranean region, often cultivated for its medicinal properties.
Scientific name: Papaver somniferum
Name: Opopanax
Order: Apiales
Habitat: Middle East
Scientific name: Commiphora gileadensis
Name: Opuntia gosseliniana
Order: Caryophyllales
Habitat: Mexico
Scientific name: Opuntia gosseliniana
Name: Orange Bloodwood
Order: Myrtales
Habitat: Native to eastern Australia, often found in subtropical rainforests.
Scientific name: Baloghia inophylla
Name: Orange Boxwood
Order: Buxales
Habitat: China
Scientific name: Buxus harlandii
Name: Orange Jasmine
Order: Sapindales
Habitat: Tropical Asia
Scientific name: Murraya paniculata
Name: Orange Jessamine
Order: Sapindales
Habitat: Asia
Scientific name: Murraya paniculata
Name: Orange-Barked Acacia
Order: Fabales
Habitat: Native to eastern Africa, often found in savanna and woodland habitats.
Scientific name: Acacia xanthophloea
Name: Oraon Teak
Order: Lamiales
Habitat: India
Scientific name: Tectona grandis var. rubra
Name: Orchard Myrtle
Order: Myrtales
Habitat: Asia
Scientific name: Syzygium jambos
Name: Orchid Tree
Order: Fabales
Habitat: Tropics worldwide
Scientific name: Bauhinia spp.
Name: Oregon Ash
Order: Lamiales
Habitat: Pacific Northwest
Scientific name: Fraxinus latifolia
Name: Oregon Boxwood
Order: Buxales
Habitat: Western North America
Scientific name: Pachystima myrsinites
Name: Oregon Crabapple
Order: Rosales
Habitat: Pacific Northwest
Scientific name: Malus fusca
Name: Oregon Douglas Fir
Order: Pinales
Habitat: Western North America
Scientific name: Pseudotsuga menziesii var. menziesii
Name: Oregon Myrtle
Order: Laurales
Habitat: Western United States
Scientific name: Umbellularia californica
Name: Oregon Oak
Order: Fagales
Habitat: Western United States
Scientific name: Quercus garryana var. breweri
Name: Oreomunnea Mexicana
Order: Juglandales
Habitat: Mexico
Scientific name: Oreomunnea mexicana
Name: Oriental Arborvitae
Order: Pinales
Habitat: Northeast Asia
Scientific name: Platycladus orientalis
Name: Oriental Cherry
Order: Rosales
Habitat: East Asia
Scientific name: Prunus serrulata
Name: Oriental Persimmon
Order: Ericales
Habitat: East Asia
Scientific name: Diospyros kaki
Name: Orihuela Oak
Order: Fagales
Habitat: Spain
Scientific name: Quercus orihuelensis
Name: Orinoco Ebony
Order: Fabales
Habitat: Venezuela
Scientific name: Caesalpinia ebano
Name: Ornamental Pear
Order: Rosales
Habitat: Native to China, often cultivated as an ornamental tree in urban areas.
Scientific name: Pyrus calleryana
Name: Oro Blanco
Order: Sapindales
Habitat: Mexico
Scientific name: Casimiroa tetrameria
Name: Orothamnus Zeyheri
Order: Proteales
Habitat: South Africa
Scientific name: Orothamnus zeyheri
Name: Osadhara
Order: Proteales
Habitat: India
Scientific name: Helicia robusta
Name: Osage Orange
Order: Rosales
Habitat: Central United States
Scientific name: Maclura pomifera
Name: Osage-Orange
Order: Rosales
Habitat: Central United States
Scientific name: Maclura pomifera
Name: Osceola Pine
Order: Pinales
Habitat: Southeastern United States
Scientific name: Pinus clausa
Name: Osha
Order: Apiales
Habitat: Native to western North America, often found in alpine and subalpine habitats.
Scientific name: Ligusticum porteri
Name: Oshá
Order: Apiales
Habitat: Southwestern United States
Scientific name: Ligusticum porteri
Name: Osmananthus
Order: Lamiales
Habitat: Asia
Scientific name: Osmanthus spp.
Name: Osmanthus
Order: Lamiales
Habitat: Asia
Scientific name: Osmanthus spp.
Name: Osmaronia cerasiformis
Order: Rosales
Habitat: Western United States
Scientific name: Oemleria cerasiformis
Name: Ostrich Plume Tree
Order: Proteales
Habitat: Australia
Scientific name: Grevillea robusta
Name: Ostrya
Order: Betulales
Habitat: Native to temperate regions of the Northern Hemisphere, often found in moist, well-drained soils in forests.
Scientific name: Ostrya spp.
Name: Ostrya Japonica
Order: Betulales
Habitat: Japan
Scientific name: Ostrya japonica
Name: Ostrya Virginia
Order: Betulales
Habitat: Eastern North America
Scientific name: Ostrya virginiana
Name: Otaheite Apple
Order: Myrtales
Habitat: Polynesia
Scientific name: Syzygium malaccense
Name: Ottawa Oak
Order: Fagales
Habitat: North America
Scientific name: Quercus ellipsoidalis
Name: Ottoschulzia
Order: Aquifoliales
Habitat: Caribbean
Scientific name: Ottoschulzia rhodoxylon
Name: Ouabain Tree
Order: Apocynales
Habitat: Africa
Scientific name: Strophanthus gratus
Name: Ouazaizait
Order: Fagales
Habitat: North Africa
Scientific name: Quercus afares
Name: Ougi
Order: Rosales
Habitat: Asia
Scientific name: Kalopanax septemlobus
Name: Oumafou
Order: Fabales
Habitat: Central Africa
Scientific name: Millettia laurentii
Name: Oumandjou
Order: Proteales
Habitat: India
Scientific name: Helicia robusta
Name: Ourea
Order: Sapindales
Habitat: Brazil and Guyana
Scientific name: Tapirira obtusa
Name: Ourolho
Order: Sapindales
Habitat: South America
Scientific name: Myrcianthes pungens
Name: Outeniqua Yellowwood
Order: Podocarpales
Habitat: South Africa
Scientific name: Podocarpus falcatus
Name: Overland Blackbead
Order: Fabales
Habitat: Mexico and Central America
Scientific name: Pithecellobium dulce
Name: Oyama Magnolia
Order: Magnoliales
Habitat: Asia
Scientific name: Magnolia obovata
Name: Ozark Chinkapin
Order: Fagales
Habitat: Central United States
Scientific name: Castanea ozarkensis
Name: Ozark Witch Hazel
Order: Saxifragales
Habitat: Central United States
Scientific name: Hamamelis vernalis
| Name | Order | Habitat | Scientific name |
|---|---|---|---|
| Oahu Alectryon | Sapindales | Native to Hawaii | Alectryon macrococcus |
| Oak | Fagales | Temperate forests | Quercus |
| Oak Leaf Hydrangea | Ericales | Native to southeastern United States, often found in moist, well-drained soils in forests and along stream banks. | Hydrangea quercifolia |
| Oaks and Pine | Fagales | Temperate forests | Quercus spp. |
| Oaxacan Rosewood | Fabales | Central America | Dalbergia congestiflora |
| Oban Pine | Pinales | Mexico | Pinus oaxacana |
| Oblique-leaved Alangium | Cornales | Southeast Asia | Alangium obliquum |
| Oblong Aralia | Apiales | East Asia | Aralia cordata |
| Oblong Burr Oak | Fagales | Central United States | Quercus macrocarpa var. oliviformis |
| Oblong-leaved Yellowwood | Proteales | Southern Africa | Podocarpus latifolius |
| Ocania Myrtle | Myrtales | Peru | Eugenia ocaina |
| Ocaña Oak | Fagales | Colombia | Quercus ocaneana |
| Occidental Plane Tree | Proteales | Native to eastern North America | Platanus occidentalis |
| Ochna | Malpighiales | Tropical Africa and Asia | Ochna spp. |
| Ochrocarpos | Malpighiales | Africa | Ochrocarpos africanus |
| Ochroma Pyramidale | Malvales | Central and South America | Ochroma pyramidale |
| Ocoee Silverbell | Ericales | Southeastern United States | Halesia tetraptera var. monticola |
| Ocotea | Laurales | Central and South America | Ocotea spp. |
| Ocotea Cernua | Laurales | South America | Ocotea cernua |
| Ocotea Cymbarum | Laurales | South America | Ocotea cymbarum |
| Ocotea Foetens | Laurales | Canary Islands | Ocotea foetens |
| Ocotea Martinicensis | Laurales | Lesser Antilles | Ocotea martinicensis |
| Ocotea Oblonga | Laurales | Central America | Ocotea oblonga |
| Ocotea Rubra | Laurales | South America | Ocotea rubra |
| Ocotea Viridiflora | Laurales | South America | Ocotea viridiflora |
| Ocotillo | Caryophyllales | Southwestern United States and Mexico | Fouquieria splendens |
| Ocuba Palm | Arecales | South America | Oenocarpus bataua |
| Odina Woodier | Sapindales | Asia | Lannea coromandelica |
| Odoardo's Crab Apple | Rosales | China | Malus odoardi |
| Odontadenia Macrantha | Gentianales | South America | Odontadenia macrantha |
| Odontoglossum | Asparagales | Tropical America | Odontoglossum spp. |
| Oecus | Sapindales | Southeast Asia | Oecus dipsaceus |
| Oenocarpus Bacaba | Arecales | South America | Oenocarpus bacaba |
| Oenocarpus Bataua | Arecales | South America | Oenocarpus bataua |
| Oenocarpus Distichus | Arecales | South America | Oenocarpus distichus |
| Offa Palm | Arecales | Brazil | Syagrus coronata |
| Officier Tree | Myrtales | Australia | Xanthostemon chrysanthus |
| Ogeechee Lime | Malvales | Southeastern United States | Nyssa ogeche |
| Ogeechee Tupelo | Ericales | Southeastern United States | Nyssa ogeche |
| Ogham Tree | Coniferales | Europe and Asia | Juniperus communis |
| Ogier Nut | Malpighiales | Brazil | Couepia longipendula |
| Ogonori | Caryophyllales | Western North America | Sarcobatus vermiculatus |
| Ohai | Fabales | Easter Island | Sophora toromiro |
| Ohi'a Lehua | Myrtales | Hawaii | Metrosideros polymorpha |
| Ohio Buckeye | Sapindales | Eastern United States | Aesculus glabra |
| Ohio Pine | Pinales | Eastern United States | Pinus strobus |
| Oho | Pittosporales | Southern Africa | Ptaeroxylon obliquum |
| Oiao | Proteales | Philippines | Helicia obovatifolia |
| Okame Cherry | Rosales | Ornamental cultivar | Prunus x incamp 'Okame' |
| Okari Nut | Proteales | New Guinea | Terminalia kaernbachii |
| Okina | Apiales | Caribbean | Dendropanax arboreus |
| Oklahoma Redbud | Fabales | Central United States | Cercis canadensis var. texensis |
| Okume | Sapindales | West Africa | Aucoumea klaineana |
| Okuta Palm | Arecales | Indonesia | Livistona okmueensis |
| Okwango Quinine Tree | Gentianales | Southern Africa | Rauvolfia caffra |
| Olacaceae | Santalales | Tropical regions | Olacaceae |
| Olallie Berry | Rosales | Native to western North America, often found in moist, shaded areas in forests and along streams. | Rubus ursinus |
| Olax Scandens | Olacales | Southeast Asia | Olax scandens |
| Old Alder | Fagales | Europe and West Asia | Alnus glutinosa |
| Old Field Pine | Pinales | Southeastern United States | Pinus palustris |
| Old Man Cactus | Caryophyllales | Mexico | Cephalocereus senilis |
| Old Man Pine | Pinales | Western Himalayas | Pinus gerardiana |
| Old World Ebony | Rosales | South Asia | Diospyros ebenum |
| Oleander | Gentianales | Mediterranean region | Nerium oleander |
| Oleaster | Rosales | Temperate regions of Europe and Asia | Elaeagnus angustifolia |
| Oleerod | Rosales | Central America | Amyris oleifera |
| Olive | Lamiales | Mediterranean climate regions | Olea europaea |
| Olive Bark Tree | Laurales | Southeast Asia | Terminalia oliveri |
| Olive Buckthorn | Rosales | Mediterranean region | Rhamnus oleoides |
| Olive Daphne | Laureales | Asia | Daphniphyllum orientale |
| Olive Hawthorn | Rosales | Eastern United States | Crataegus olivacea |
| Olive Plum | Rosales | Cultivated | Prunus amygdalus |
| Olive Tortoise Shell | Rosales | Cultivated | Blepharocaly x olea |
| Oliver's Aspen | Malpighiales | Western United States | Populus tremuloides var. oliveri |
| Olivo | Laurales | Mediterranean region | Olea europaea |
| Olneya | Fabales | Southwestern United States and Mexico | Olneya tesota |
| Olohua | Proteales | Philippines | Helicia obovatifolia |
| Olong Tree | Laurales | Southeast Asia | Cryptocarya obovata |
| Olympia Serviceberry | Rosales | Northwestern United States | Amelanchier alnifolia var. semiintegrifolia |
| Oma Oma Nut | Malpighiales | Indonesia | Barringtonia procera |
| Omalanthus Populifolius | Malpighiales | Australia | Homalanthus populneus |
| Omanine | Myrtales | Sri Lanka | Syzygium caryophyllatum |
| Omanite | Pinales | Middle East | Juniperus excelsa |
| Omanite Pine | Pinales | Oman | Pinus omanensis |
| Ombu | Asterales | South America | Phytolacca dioica |
| Ombu Tree | Caryophyllales | South America | Phytolacca dioica |
| Omoana | Malvales | West Africa | Mansonia altissima |
| Omurana | Laurales | Hawaii | Cryptocarya omurana |
| Oncoba Spinosa | Malpighiales | Africa | Oncoba spinosa |
| Onderste Bosch | Ericales | South Africa | Blumea cylindrica |
| Ondina | Laurales | Chile | Persea lingue |
| One-Seed Juniper | Pinales | Southwestern United States | Juniperus monosperma |
| Oneida Serviceberry | Rosales | Northeastern United States | Amelanchier interior |
| Onion Cedar | Cupressales | Japan | Juniperus procumbens |
| Onobrychis montana | Fabales | Europe | Onobrychis montana |
| Onondaga Oak | Fagales | Eastern United States | Quercus prinoides |
| Ontari Palm | Arecales | South America | Euterpe oleracea |
| Ooah Tree | Caryophyllales | Central Africa | Tessmannia africana |
| Oolampia | Myrtales | Australia | Syzygium oleosum |
| Oolooman Ash | Lamiales | Mexico | Fraxinus uhdei |
| Ooltewah Juniper | Pinales | Southeastern United States | Juniperus x ashei |
| Ootanga | Apiales | Coastal regions of northern Europe | Ligusticum scoticum |
| Opah | Proteales | Philippines | Helicia philippinensis |
| Opalo | Sapindales | South America | Jessenia bataua |
| Opangi Nut | Malvales | Central America | Pachira aquatica |
| Opangia | Malvales | Central America | Pachira aquatica |
| Opauca | Laurales | Brazil | Ocotea opaca |
| Opham | Fagales | Middle East | Quercus libani |
| Opichti | Pinales | Central America | Pinus oocarpa |
| Opium Poppy | Ranunculales | Native to the Mediterranean region, often cultivated for its medicinal properties. | Papaver somniferum |
| Opopanax | Apiales | Middle East | Commiphora gileadensis |
| Opuntia gosseliniana | Caryophyllales | Mexico | Opuntia gosseliniana |
| Orange Bloodwood | Myrtales | Native to eastern Australia, often found in subtropical rainforests. | Baloghia inophylla |
| Orange Boxwood | Buxales | China | Buxus harlandii |
| Orange Jasmine | Sapindales | Tropical Asia | Murraya paniculata |
| Orange Jessamine | Sapindales | Asia | Murraya paniculata |
| Orange-Barked Acacia | Fabales | Native to eastern Africa, often found in savanna and woodland habitats. | Acacia xanthophloea |
| Oraon Teak | Lamiales | India | Tectona grandis var. rubra |
| Orchard Myrtle | Myrtales | Asia | Syzygium jambos |
| Orchid Tree | Fabales | Tropics worldwide | Bauhinia spp. |
| Oregon Ash | Lamiales | Pacific Northwest | Fraxinus latifolia |
| Oregon Boxwood | Buxales | Western North America | Pachystima myrsinites |
| Oregon Crabapple | Rosales | Pacific Northwest | Malus fusca |
| Oregon Douglas Fir | Pinales | Western North America | Pseudotsuga menziesii var. menziesii |
| Oregon Myrtle | Laurales | Western United States | Umbellularia californica |
| Oregon Oak | Fagales | Western United States | Quercus garryana var. breweri |
| Oreomunnea Mexicana | Juglandales | Mexico | Oreomunnea mexicana |
| Oriental Arborvitae | Pinales | Northeast Asia | Platycladus orientalis |
| Oriental Cherry | Rosales | East Asia | Prunus serrulata |
| Oriental Persimmon | Ericales | East Asia | Diospyros kaki |
| Orihuela Oak | Fagales | Spain | Quercus orihuelensis |
| Orinoco Ebony | Fabales | Venezuela | Caesalpinia ebano |
| Ornamental Pear | Rosales | Native to China, often cultivated as an ornamental tree in urban areas. | Pyrus calleryana |
| Oro Blanco | Sapindales | Mexico | Casimiroa tetrameria |
| Orothamnus Zeyheri | Proteales | South Africa | Orothamnus zeyheri |
| Osadhara | Proteales | India | Helicia robusta |
| Osage Orange | Rosales | Central United States | Maclura pomifera |
| Osage-Orange | Rosales | Central United States | Maclura pomifera |
| Osceola Pine | Pinales | Southeastern United States | Pinus clausa |
| Osha | Apiales | Native to western North America, often found in alpine and subalpine habitats. | Ligusticum porteri |
| Oshá | Apiales | Southwestern United States | Ligusticum porteri |
| Osmananthus | Lamiales | Asia | Osmanthus spp. |
| Osmanthus | Lamiales | Asia | Osmanthus spp. |
| Osmaronia cerasiformis | Rosales | Western United States | Oemleria cerasiformis |
| Ostrich Plume Tree | Proteales | Australia | Grevillea robusta |
| Ostrya | Betulales | Native to temperate regions of the Northern Hemisphere, often found in moist, well-drained soils in forests. | Ostrya spp. |
| Ostrya Japonica | Betulales | Japan | Ostrya japonica |
| Ostrya Virginia | Betulales | Eastern North America | Ostrya virginiana |
| Otaheite Apple | Myrtales | Polynesia | Syzygium malaccense |
| Ottawa Oak | Fagales | North America | Quercus ellipsoidalis |
| Ottoschulzia | Aquifoliales | Caribbean | Ottoschulzia rhodoxylon |
| Ouabain Tree | Apocynales | Africa | Strophanthus gratus |
| Ouazaizait | Fagales | North Africa | Quercus afares |
| Ougi | Rosales | Asia | Kalopanax septemlobus |
| Oumafou | Fabales | Central Africa | Millettia laurentii |
| Oumandjou | Proteales | India | Helicia robusta |
| Ourea | Sapindales | Brazil and Guyana | Tapirira obtusa |
| Ourolho | Sapindales | South America | Myrcianthes pungens |
| Outeniqua Yellowwood | Podocarpales | South Africa | Podocarpus falcatus |
| Overland Blackbead | Fabales | Mexico and Central America | Pithecellobium dulce |
| Oyama Magnolia | Magnoliales | Asia | Magnolia obovata |
| Ozark Chinkapin | Fagales | Central United States | Castanea ozarkensis |
| Ozark Witch Hazel | Saxifragales | Central United States | Hamamelis vernalis |