4,295 articles
Orchids of Madagascar
The orchids of Madagascar are a highly endemic flora of about 1,000 species in 53 genera, famous for Darwin's 1862 prediction of a long-tongued hawkmoth pollinator.
Orchids of New Zealand
The orchids of New Zealand comprise about 117 species in 24 to 27 genera, mostly small terrestrial ground orchids, with greenhoods (Pterostylis) the largest genus.
Orchids of North America
The orchids of North America are the roughly 210 orchid species native north of Mexico plus about 2,670 Mesoamerican species, with richness rising steeply toward the tropics.
Orchids of South America
Orchids of South America covers the continent's orchid diversity: Colombia, Ecuador, and Brazil lead with thousands of species each, concentrated in the Andes and Atlantic Forest.
Orchids of subantarctic and oceanic islands
The orchids of subantarctic and oceanic islands are the exceptionally sparse orchid floras of remote islands, with Macquarie Island at 55°S marking the family's southernmost limit.
Orchids of the Caribbean
The orchids of the Caribbean are the roughly 600 to 728 orchid species native to the West Indies, where 42 to 72 percent of species grow nowhere else.
Orchids of the Pacific Islands
The orchids of the Pacific Islands are the orchid floras of Melanesia, Micronesia, and Polynesia in Oceania, where a survey of 63 islands found 552 species in 110 genera.
Orchis
Orchis (Tourn. ex L., 1753) is a genus of about 20 terrestrial Eurasian orchids in Orchidaceae, subtribe Orchidinae, type species O. militaris; formerly broader, now excluding Anacamptis and Neotinea, growing on calcareous soils.
Oregano
Oregano, chiefly Origanum vulgare (wild marjoram), a Lamiaceae perennial herb of the Mediterranean; flavor from carvacrol and thymol; Mexican oregano is Lippia graveolens; world trade exceeds 15,000 tonnes.
Origanum
Origanum is a Lamiaceae genus of about 40-44 aromatic species native from Macaronesia and Europe to Central China, 90% Mediterranean. Includes oregano (O. vulgare, cymyl/carvacrol chemotype) and sweet marjoram (O. majorana, sabinyl chemotype).
Ornamental alliums
Ornamental alliums are bulbous members of the genus Allium, grown in gardens for their spherical flower heads in late spring and early summer, with about 250 ornamental species and 240 cultivars in the trade.
Ornamental plant
Ornamental plant: a plant grown for decoration rather than food or raw materials, spanning cut flowers, houseplants, bedding plants, and trees and shrubs; a roughly 27 billion USD (2021) industry led by the Netherlands and dominated by roses, chrysanthemums, carnations, gerberas, tulips, and lilies.
Ornithogalum
Ornithogalum is a genus of bulbous flowering plants in the asparagus family, native from Europe to Afghanistan and southern Africa, known in gardens as star of Bethlehem.
Ornithopus
Ornithopus (bird's-foot, serradella) is a genus of six annual legume species in Fabaceae, tribe Loteae, native from Macaronesia and Europe to Iran and disjunctly to South America; O. sativus is a widely sown forage legume on acidic sandy soils.
Ornithopus sativus
Ornithopus sativus, known as French serradella or pink serradella, is an annual legume in the pea family, native to southwestern Europe and northwestern Africa and grown as forage.
Orobanchaceae
Orobanchaceae (broomrape family), Ventenat 1799, is the largest family of parasitic flowering plants in Lamiales, with over 2,000 species in about 90-115 genera, spanning non-parasitic, hemiparasitic, and holoparasitic members including Striga and Orobanche crop pests.
Orobanche
Orobanche (broomrapes), holoparasitic Orobanchaceae genus published 1753; chlorophyll-free root parasites on Asteraceae and other hosts; 174 species in 2025 broad circumscription; crop pests like O. crenata and O. cumana.
Orris root
Orris root: dried, aged rhizomes of Iris germanica, I. pallida, and I. florentina, source of violet-scented irones for perfume (orris butter) and gin flavoring; irones form only after 3–5 years of curing.
Orthosiphon
Orthosiphon (syn. Clerodendranthus) is a genus of 45 accepted Lamiaceae species native from Colombia and Africa to northeast Australia; its best-known species, O. aristatus or O. stamineus (cat's whiskers, misai kucing), is a Southeast Asian medicinal plant used as a diuretic and studied for antidiabetic effects.
Orthotrichales
Orthotrichales is an order of mosses (Bryophyta, Bryopsida) centered on the Orthotrichaceae, about 900 epiphytic species; includes yoke-, bristle-mosses, and pincushions; rbcL data suggest the order is polyphyletic.
Oryza
Oryza is a genus of grasses containing the two domesticated rices, Asian rice and African rice, plus wild relatives, native to the tropics and subtropics.
Oryza glaberrima
Oryza glaberrima, African rice, one of only two cultivated rice species, independently domesticated in West Africa from Oryza barthii about 2,000–3,000 years ago; hardy but low-yielding, displaced by O. sativa and used in NERICA hybrids.
Oryza sativa
Oryza sativa, Asian rice, staple cereal domesticated from Oryza rufipogon in the Yangtze valley (japonica) with indica formed by introgression; feeds over half the world's population.
Osmanthus
Osmanthus (sweet olive, tea olive; 桂花 for O. fragrans) is a genus of about 26–30 fragrant evergreen Oleaceae shrubs from Türkiye to Japan and Indo-China, used in tea, food, and perfumery.
Osmanthus fragrans
Osmanthus fragrans (桂花, guìhuā), sweet osmanthus or tea olive, is an Oleaceae tree native from the Himalaya to southern Japan, cultivated in China for 2,500 years for fragrant flowers used in tea, sweets, medicine, and perfumery.
Osmunda
Osmunda, royal ferns of Osmundaceae, a cosmopolitan genus of 13 wetland fern species published by Linnaeus in 1753, known as fossils since the Late Triassic about 220 million years ago.
Osmunda japonica
Osmunda japonica (zenmai, ゼンマイ; 紫萁; 고비), the Japanese royal fern, is an Osmundaceae fern from Pakistan to Sakhalin and Indochina with dimorphic 2-pinnate fronds, 2n=44, edible spring fiddleheads, and hybrids O. hybrida, O. × intermedia, O. × nipponica, and O. × mildei.
Osmunda regalis
Osmunda regalis, the royal fern, is an Old World Osmundaceae fern native from Europe and Macaronesia to Africa and Madagascar, hemidimorphic with apical fertile pinnae, IUCN least concern, and distinct from American O. spectabilis.
Osmundaceae
Osmundaceae (royal ferns), order Osmundales, a family of leptosporangiate ferns sister to all other leptosporangiates; fewer than 20 species in four to six genera but the richest fossil record of any extant fern group, from the Permian onward.
Osmundastrum
Osmundastrum, cinnamon fern (formerly Osmunda cinnamomea), a monotypic royal-fern genus (Osmundaceae) split from Osmunda on molecular evidence; its single species is an eastern Asia–eastern North America disjunct wetland fern with dimorphic fronds.