Seed plants

Ocimum tenuiflorum

Ocimum tenuiflorum, holy basil or tulsi (तुलसी), synonym Ocimum sanctum, is a Lamiaceae perennial herb native to tropical Asia, sacred in Hinduism, rich in eugenol and ursolic acid, and studied in stress and metabolic clinical trials.

Oenothera

Oenothera (evening primroses) is a New World genus of about 140-156 herbaceous species in Onagraceae, famous as de Vries's mutation-theory plant, with biparental chloroplast inheritance, Renner complexes, and seed oil rich in gamma-linolenic acid.

Oenothera biennis

Oenothera biennis, the common evening primrose, is a biennial herb native to North America with bright yellow flowers that open at night, grown as the source of evening primrose oil.

Olacaceae

Olacaceae (R.Br. 1818, nom. cons.) is a pantropical family of Santalales with trees, shrubs, and climbers, about 25-29 genera and roughly 250 species; traditionally circumscribed Olacaceae is paraphyletic and has been split into narrower families including Erythropalaceae and Strombosiaceae.

Old Tjikko

Old Tjikko is a Norway spruce (Picea abies) located on Fulufjället, Dalarna Province, Sweden. Its root system is dated to about 9,500 years, making it a notable living clone.

Olea

Olea is a genus of about 32 evergreen Oleaceae trees and shrubs of the Old World, including the olive Olea europaea with six subspecies, over 1,000 cultivars, and the wild oleaster var. sylvestris.

Oleaceae

Oleaceae, the olive family (Hoffmanns. & Link, 1809), is a family of Lamiales with 25-27 genera and c. 600-615 species of trees, shrubs, and woody climbers, including Olea europaea, Fraxinus, Jasminum, and Syringa, recognized by opposite estipulate leaves and 4-merous flowers with 2 stamens.

Olearia

Olearia (daisy bush), genus of evergreen Asteraceae shrubs and small trees, about 180 species in Australia, New Zealand, and New Guinea; shown polyphyletic since 2002 and being split into Shawia and other genera.

Olein

Olein is the liquid fraction obtained when palm oil or another vegetable oil is fractionated from its solid stearin, used in cooking oils and margarine.

Olive

Olive (Olea europaea), Mediterranean evergreen tree of Oleaceae cultivated for table fruit and olive oil; wild form is the oleaster. Levant domestication from Chalcolithic times, alternate bearing, oleuropein bitterness, Xylella threat.

Olive oil

Olive oil, the oil pressed from Olea europaea fruit, graded extra virgin (free acidity ≤0.8%), virgin, refined, or pomace by IOC and USDA standards; EU produces ~67% of world supply; UC Davis studies found many imported "extra virgin" oils fail standards.

Oliveriana

Oliveriana Rchb.f. is a genus of 15 accepted Oncidiinae orchid species native from western South America to Guyana, named for botanist Daniel Oliver; type species O. egregia, described 1876.

Omacetaxine mepesuccinate

Omacetaxine mepesuccinate (Synribo), formerly homoharringtonine, is a semisynthetic cephalotaxine protein synthesis inhibitor binding the 80S ribosome, FDA-approved October 26, 2012 for CML resistant or intolerant to two or more tyrosine kinase inhibitors, including T315I-mutant disease.

Omurice (オムライス)

Omurice (オムライス, omuraisu) is Japanese yoshoku comfort food: ketchup-seasoned chicken rice wrapped in a thin omelette. Origin claimed by Rengatei (Tokyo, c. 1900) and Hokkyokusei (Osaka, 1925); styles include ganso, fuwatoro, and Kichi Kichi's viral sliced-open version.

Onagraceae

Onagraceae, the evening primrose family (Onagraceae Juss., nom. cons., 1789), a Myrtales family of about 650 species in 22-23 genera, mostly New World herbs and shrubs with 4-merous flowers, inferior ovaries, and viscin-threaded pollen; includes Oenothera, Fuchsia, Clarkia, Epilobium, Ludwigia.

Oncidium

Oncidium (dancing ladies, butterfly orchid) is a neotropical orchid genus of about 339 accepted species with pseudobulbs and showy sprays; DNA studies merged Odontoglossum and other genera into it, and it is widely grown as a cut-flower and pot orchid.

Onigiri (おにぎり)

Onigiri (おにぎり), also omusubi, is the Japanese hand-pressed rice ball, typically triangular, salted, nori-wrapped, and filled with umeboshi, salmon, or tuna mayo; a staple of bento and convenience stores with a history from Yayoi-era carbonized rice to the 1978 film-packaging era.

Onion

Onion (Allium cepa), bulb crop of the amaryllis family from central Asia, cultivated over 4,700 years; bulbing is day-length controlled; second only to tomato in global production.

Onobrychis

Onobrychis (sainfoins), Fabaceae genus published by Miller in 1754, native Europe to Mongolia, Arabia, Ethiopia; about 130–208 species; includes forage legume sainfoin O. viciifolia, non-bloating, tannin-rich.

Onobrychis viciifolia

Onobrychis viciifolia (common sainfoin) is a perennial Fabaceae forage legume native to Central and SE Europe, non-bloating due to condensed tannins, drought tolerant via a deep taproot, and under study as a protein-rich perennial pulse crop.

Ononis

Ononis (restharrow), Fabaceae genus of about 88 annual/perennial herbs and shrubs, Mediterranean-centered, monadelphous stamens, dimorphic anthers, used in medicine and as forage.

Operculina

Operculina Silva Manso is a pantropical genus of climbing vines in Convolvulaceae, type species O. turpethum, defined by an operculate capsule; includes medicinal jalapa and turpeth species.

Ophrys

Ophrys (bee orchids) is a Mediterranean-centered orchid genus pollinated by sexual deception: flowers mimic female insects' looks and sex pheromones, inducing pseudocopulation by males; species counts range from nine to 400+.

Ophrys apifera

Ophrys apifera, known as the bee orchid, is a European orchid whose flower mimics a female bee; unlike most of its genus, it pollinates itself by wind.

Opuntia

Opuntia (prickly pear, cactus pear) is a genus of about 150 American cacti with jointed cladodes, glochids, and edible fruits, used for food, forage, and cochineal dye, and invasive in many regions.

Opuntia decumbens

Opuntia decumbens Salm-Dyck is a prickly pear cactus in the family Cactaceae, native from Mexico to Central America, first published in 1834 in the Hortus Dyckensis.

Opuntia leucotricha

Opuntia leucotricha, called nopal duraznillo in Spanish and Aaron's-beard prickly-pear in English, is a prickly pear cactus from the Altiplano of central Mexico that grows 3 to 4 m tall with white hair-like spines.

Orbea

Orbea Haw. (1812) is a genus of about 60 stem-succulent stapeliads in Apocynaceae, native to Africa and the Arabian Peninsula, with carrion-scented fly-pollinated flowers; type species Orbea variegata.

Orchid

Orchid (Orchidaceae): one of the largest flowering-plant families, over 700 genera and roughly 30,000 species on all continents except Antarctica; defined by bilateral flowers, dust-like mycorrhiza-dependent seeds, deceptive pollination, CITES protection, and major horticultural trade.