Atlas of the Flora of New England

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Genera - O

Ocimum
Oclemena
Odontites
Oenothera
Oligoneuron (see Solidago)
Omaltheca
Onoclea
Onopordum
Onosmodium (see Lithospermum)
Ophioglossum
Opuntia
Orchis (see Amerorchis & Galearis)
Origanum
Ornithogalum
Ornithopus
Orobanche
Orontium
Orthilia
Oryzopsis (see also Patis and Piptatheropsis)
Osmorhiza
Osmunda (see also Osmundastrum)
Osmundastrum
Ostrya
Oxalis
Oxybasis
Oxycoccus (see Vaccinium)
Oxydendron
Oxyria
Oxytropis


OCIMUM (Family: Lamiaceae)


OCIMUM BASILICUM Linnaeus - Sweet Basil. 2n = (30), 48, 52, 72.


Waste places. Possibly from Africa.



OCLEMENA (Family: Asteraceae)


Oclemena acuminata (Michaux) Greene - Mountain Aster. 2n = 18.


Woods, often acidic. [Aster acuminatus Michaux]


Oclemena nemoralis (Aiton) Greene - Bog Aster. 2n = 18.


Sphagnum bogs and shores. [Aster nemoralis Aiton]


Oclemena hybrid

Oclemena X blakei (Porter) G.L. Nesom - .


[O. acuminata (Michaux) Greene X O. nemoralis (Aiton) Greene; Aster blakei (Porter) House]



ODONTITES (Family: Orobanchaceae)


ODONTITES VULGARIS Moench - Red Bartsia. 2n = 18, (20).


Dry fields, roadsides, waste places. From Eurasia. [O. SEROTINUS misapplied; O. VERNUS (Bellardi) Dumortier subsp. SEROTINUS misapplied]



OENOTHERA (Family: Onagraceae)


OENOTHERA AFFINIS Cambessèdes - . 2n = ?


Waste places. From South America.


Oenothera biennis Linnaeus - Common Evening-Primrose. 2n = 14.


Roadsides, fields, waste places, river thickets. [O. biennis var. pycnocarpa (G.F. Atkinson & Bartlett) Wiegand]


OENOTHERA CURTIFLORA W.L. Wagner & Hoch - . 2n = 14.


Waste places. From farther west. [GAURA PARVIFLORA Douglas ex Lehmann]


Oenothera fruticosa Linnaeus subsp. fruticosa - Southern Sundrops. 2n = 56.


Salt marsh margins, meadows, swamps, fields. [O. fruticosa var. eamesii (B.L. Robinson) S.F. Blake; O. fruticosa var. humifusa Allen; O. fruticosa var. linearis (Michaux) S. Watson; O. tetragona Roth var. longistipata (Pennell) Munz]


Oenothera fruticosa Linnaeus subsp. tetragona (Roth) W.L. Wagner - . 2n = 28.


Gravelly, sandy eskers, dry fields and banks, woodland margins, waste places. [O. fruticosa Linnaeus subsp. glauca (Michaux) Straley; O. tetragona Roth var. tetragona]


OENOTHERA GAURA W.L. Wagner & Hoch - . 2n = 14.


Roadsides, waste places, dry thickets. From farther south and west. [GAURA BIENNIS Linnaeus]


OENOTHERA GLAZIOVIANA Micheli - . 2n = 14.


Roadsides, waste places, fields. From farther south and west. [O. ERYTHROSEPALA Borbás]


OENOTHERA GRANDIFLORA L’Héritier - . 2n = 14.


Roadsides, waste places. From farther south. [O. BIENNIS Linnaeus var. GRANDIFLORA (L’Héritier ex Aiton) Torrey & A. Gray]


OENOTHERA GRANDIS (Britton) Smyth - . 2n = 14.


Fields. From farther west.


OENOTHERA LACINIATA Hill - . 2n = 14.


Waste places, roadsides, fields, usually in dry, sandy, open soil. From farther south and west.


Oenothera nutans G.F. Atkinson & Bartlett - . 2n = 14.


River thickets. [O. biennis Linnaeus var. nutans (G.F. Atkinson & Bartlett) Wiegand]


Oenothera oakesiana (A. Gray) J.W. Robbins ex S. Watson & J.M. Coulter - . 2n = 14.


Open, sandy areas of beaches, dunes, roadsides and fields. [O. cruciata Nuttall ex G. Don var. stenopetala (E.P. Bicknell) Fernald; O. parviflora Linnaeus var. angustissima (R.R. Gates) Wiegand; O. parviflora Linnaeus var. oakesiana (A. Gray) Fernald)]


Oenothera parviflora Linnaeus - . 2n = 14.


Streambanks, thickets, roadsides, railroads, fields, dry sand or gravel. [O. biennis Linnaeus var. cruciata (Nuttall ex G. Don) Torrey & A. Gray; O. cruciata Nuttall ex G. Don var. cruciata]


Oenothera perennis Linnaeus - Little Sundrops. 2n = 14.


Dry fields, clearings, roadsides, waste places, meadows.


OENOTHERA PILOSELLA Rafinesque - . 2n = 56.


Dry woodlands, fields, roadsides, rocky shores, waste places. From farther west and south.


OENOTHERA SERRULATA Nuttall - . 2n = 14.


Railroads. From farther west. [CALYLOPHUS SERRULATUS (Nuttall) P.H. Raven]


OENOTHERA SPECIOSA Nuttall - White Evening-Primrose. 2n = 14.


Waste places, roadsides. From farther west and south.


OENOTHERA VILLOSA Thunberg subsp. VILLOSA - . 2n = 14.


Fields, roadsides, waste places, beaches. From farther west. [O. DEPRESSA Greene]



OMALTHECA (Family: Asteraceae)


Omalotheca supina (Linnaeus) de Candolle - Alpine Cudweed. 2n = 28.


Granitic alpine areas. [Gnaphalium supinum Linnaeus]


Omalotheca sylvatica (Linnaeus) Schultz-Bipontinus & F.W. Schultz - Heath Cudweed. 2n = 56.


Clearings, rocky slopes, woods borders. [Gnaphalium sylvaticum Linnaeus]



ONOCLEA (Family: Onocleaceae)


Onoclea sensibilis Linnaeus - Sensitive Fern. 2n = 74.


Swamps, low woods, alluvial thickets, meadows, in neutral to slightly acid soils. [O. sensibilis var. obtusilobata (Schkuhr) Torrey]



ONOPORDUM (Family: Asteraceae)


ONOPORDUM ACANTHIUM Linnaeus subsp. ACANTHIUM - Cotton Thistle. 2n = 34.


Waste places, roadsides, gravelly, sandy tidal shores. From Eurasia.



OPHIOGLOSSUM (Family: Ophioglossaceae)


Ophioglossum pusillum Rafinesque - Northern Adder's Tongue. 2n = 960.


Peaty or grassy swales, meadows, damp thickets, damp sands. [O. vulgatum Linnaeus var. pseudopodum (S.F. Blake) Farwell]


Ophioglossum vulgatum Linnaeus - Southern Adder's Tongue. 2n = 240, 480, ca. 486, ca. 540.


Rich wooded slopes, floodplain woods.



OPUNTIA (Family: Cactaceae)


Opuntia humifusa (Rafinesque) Rafinesque var. humifusa - Eastern Prickly-pear. 2n = 22, 44.


Dry, exposed ledges and sandy fields.



ORIGANUM (Family: Lamiaceae)


ORIGANUM VULGARE Linnaeus subsp. VULGARE - Wild Marjoram. 2n = 30, 32.


Waste places, roadsides, railroads, fields, woodlands, brooksides, meadows. From Eurasia, northwestern Africa.



ORNITHOGALUM (Family: Asparagaceae)


ORNITHOGALUM NUTANS Linnaeus - . 2n = 14, 18, 19, 35, 45.


Low meadows, fields. From western Asia.


ORNITHOGALUM UMBELLATUM Linnaeus - Star-of-Bethlehem. 2n = 16, 18, 27, 36, 45, 52, 54, 72, 90.


Old house sites, roadsides, thickets, fields, meadows. From Europe.



ORNITHOPUS (Family: Fabaceae)


ORNITHOPUS SATIVUS Brotero subsp. SATIVUS - Serradella. 2n = 14.


Sandy, open, disturbed soil. From southwestern Europe, northern Africa.



OROBANCHE (Family: Orobanchaceae)


Orobanche uniflora Linnaeus - One-flowered Cancer-root. 2n = 18.


Damp woods and thickets, streambanks, parasitic on roots of various plants.



ORONTIUM (Family: Araceae)


Orontium aquaticum Linnaeus - Golden Club. 2n = 26.


Shallow water of ponds, sandy, muddy or sphagnous shores.



ORTHILIA (Family: Ericaceae)


Orthilia secunda (Linnaeus) House - One-sided Pyrola. 2n = 38.


Rich woods. [Pyrola secunda Linnaeus; P. secunda var. obtusata Turczaninow]



ORYZOPSIS (Family: Poaceae)


Oryzopsis asperifolia Michaux - . 2n = 46, 48.


Dry woods.



OSMORHIZA (Family: Apiaceae)


Osmorhiza berteroi de Candolle - Mountain Sweet Cicely. 2n = 22.


Rich woodlands. [O. chilensis Hooker & Arnott]


Osmorhiza claytonii (Michaux) C.B. Clarke - Hairy Sweet Cicely. 2n = 22.


Rich woodlands.


Osmorhiza depauperata Philippi - . 2n = 22.


Moist, deciduous woodlands. [O. obtusa (J.M. Coulter & Rose) Fernald]


Osmorhiza longistylis (Torrey) de Candolle - Anise-root. 2n = 22.


Rich, moist woodlands. [O. longistylis var. brachycoma S.F. Blake; O. longistylis var. villicaulis Fernald]



OSMUNDA (Family: Osmundaceae)


Osmunda claytoniana Linnaeus - Interrupted Fern. 2n = 44.


Moist woods, margins of swamps, moist thickets, occasionally in the open, in acid or neutral soils.


Osmunda regalis Linnaeus var. spectabilis (Willdenow) A. Gray - Royal Fern. 2n = 44.


Swamps, peaty thickets, shores, meadows, bogs, mostly in acid soils.

Osmunda hybrid

Osmunda X ruggii R.M. Tryon.


[O. claytoniana Linnaeus X O. regalis Linnaeus var. spectabilis (Willdenow) A. Gray]



OSMUNDASTRUM (Family: Osmundaceae)


Osmundastrum cinnamomeum (Linnaeus) C. Presl - Cinnamon Fern. 2n = 44.


Swamps, damp thickets, stream banks, and other moist, shaded places in acid soils. [Osmunda cinnamomea Linnaeus; O. cinnamomea var. glandulosa Waters]



OSTRYA (Family: Betulaceae)


Ostrya virginiana (Miller) K. Koch - American Hop-Hornbeam. 2n = 16.


Rich, dry woods. [O. virginiana var. lasia Fernald]



OXALIS (Family: Oxalidaceae)


OXALIS CORNICULATA Linnaeus - Creeping Wood-Sorrel. 2n = (12), (16), 24, (28), (32), 44, 48.


Waste places, roadsides, fields. From unknown origin.


Oxalis dillenii Jacquin - . 2n = 18, 20, 22, 24.


Dry fields, sandy thickets, woodland margins, roadsides, waste areas. [O. stricta misapplied]


Oxalis florida Salisbury - . 2n = 16.


Fields, woodland margins, sandy thickets, roadsides, waste areas. [O. filipes Small]


Oxalis montana Rafinesque - Mountain Wood-Sorrel. 2n = 22.


Rich, damp woodlands. [O. acetosella misapplied]


Oxalis stricta Linnaeus - . 2n = 18, 24.


Waste places, roadsides, fields. [O. europaea Jordan var. europaea; O. europaea var. bushii (Small) Wiegand]


Oxalis violacea Linnaeus - Violet Wood-Sorrel. 2n = 28.


Rich, moist woodlands, rocky slopes. [O. violacea var. trichophora Fassett]

Oxalis hybrid

Oxalis dillenii Jacquin X O. stricta Linnaeus.




OXYBASIS (Family: Amaranthaceae)


Oxybasis glauca (Linnaeus) S. Fuentes, Uotila & Borsch var. glaucum - Oak-leaved Goosefoot. 2n = 18, (36).


Waste places, roadsides, railroads. [Chenopodium glaucum Linnaeus var. glaucum]


OXYBASIS GLAUCA (Linnaeus) S. Fuentes, Uotila & Borsch var. SALINA (Standley) Verloove - Rocky Mountain Goosefoot. 2n = 18.


Waste places. From farther west. [CHENOPODIUM GLAUCUM Linnaeus var. SALINUM (Standley) B. Boivin; C. SALINUM Standley]


Oxybasis rubra (Linnaeus) S. Fuentes, Uotila & Borsch var. rubra - Coast Blite. 2n = (18), 36.


Salt marshes. [Chenopodium rubrum Linnaeus var. rubrum]


Oxybasis rubra (Linnaeus) S. Fuentes, Uotila & Borsch var. humilis (Hooker) Mosyakin - . 2n = 36.


Saline or brackish soil. [Chenopodium humile Hooker; C. rubrum Linnaeus var. humile (Hooker) S. Watson]


OXYBASIS URBICA (Linnaeus) S. Fuentes, Uotila & Borsch - Upright Goosefoot. 2n = 18, (36).


Waste places, wool waste. From Eurasia. [CHENOPODIUM URBICUM Linnaeus]



OXYDENDRON (Family: Ericaceae)


OXYDENDRUM ARBOREUM (Linnaeus) de Candolle - Sourwood. 2n = 24.


Woods. From farther south and west.



OXYRIA (Family: Polygonaceae)


Oxyria digyna (Linnaeus) Hill - Alpine Mountain-sorrel. 2n = 14, 42.


Alpine areas.



OXYTROPIS (Family: Fabaceae)


Oxytropis campestris (Linnaeus) de Candolle var. johannensis Fernald - 2n = 32, 48.


Rocky or gravelly river shores. [O. johannensis (Fernald) Fernald]





Designed by Ray Angelo. Revised Dec. 9, 2016