Atlas of the Flora of New England

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Genera - O

Oligoneuron (see Solidago)
Onosmodium (see Lithospermum)
Orchis (see Amerorchis & Galearis)
Oryzopsis (see also Patis and Piptatheropsis)
Osmunda (see also Osmundastrum)
Oxycoccus (see Vaccinium)

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 - . 2n = 18.

[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 clelandii W. Dietrich, P.H. Raven, & W.L. Wagner - . 2n = 14.

Fields, sandy soil.

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

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

OENOTHERA FILIFORMIS (Small) W.L. Wagner & Hoch - . 2n = 14.

Waste places, roadsides, fields. From farther south and west. [GAURA BIENNIS Linnaeus var. PITCHERI Pickering]

Oenothera fruticosa Linnaeus subsp. fruticosa - Southern Sundrops. 2n = 28, 42, 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.


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, 28, 42.

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] CONN herbarium image

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] NEBC herbarium image

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

Rich wooded slopes, floodplain woods. PH herbarium image

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.   CONN herbarium image

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.   CONN herbarium image

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 subsp. uniflora - One-flowered Cancer-root. 2n = 18, 36, 48, 72.

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.   NEBC herbarium image

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. CONN herbarium image

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

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

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] CONN herbarium image

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. glauca - Oak-leaved Goosefoot. 2n = 18, (36).

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

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 March 16, 2023