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Key to Rosa

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1 Stipules adnate to the petiole only basally, for < ½ their length; vigorous climbing vines, 3-5 (-10) m tall; petals white.
..2 Stems brown-tomentose, stipitate-glandular; terminal leaflet petiolules 3-5 mm; pedicels tomentose, 3-6 mm; hypanthia subglobose, white tomentose; [section Bracteatae]
..2 Stems glabrous, eglandular; terminal leaflet petiolules 9-13 mm; pedicels glabrous, 12-30 mm; hypanthia cupulate, densely setose [section Laevigatae]
1 Stipules adnate to the petiole > ½ their length; vigorous climbing vines or shrubs, 0.3-4 m tall; petals white, pink, rose-purple, or yellow.
....3 Styles connate into a column which protrudes from the orifice by 3-6 mm (sometimes separating in fruit); stipule margins and auricles deeply laciniate (or entire to ciliate in R. setigera); vines, climbing and scrambling to 4 m tall; [section Systylae].
......4 Leaflets 3-5; stipule margins and auricles mostly entire or ciliate; inflorescences laxly corymbose; flowers 3-5 cm in diameter, petals single, rose-purple to pink; carpels 20-25, styles glabrous, exserted 5-6 mm beyond the orifice; [native]
......4 Leaflets (5-) 7-9; stipule margins and auricles deeply laciniate; inflorescences paniculate; flowers 1.5-2.5 cm in diameter, petals single or double, white to shades of pink; carpels 6-20; styles glabrous or pubescent, exserted 3-5 mm beyond the orifice; [exotic].
........5 Pedicels 18-25 mm, glabrous, eglandular; flowers 2-2.5 cm in diameter, hypanthium elongate-ovoid, 4-6.5 mm x 2-3 mm, eglandular; carpels 12-20, styles pubescent, exserted 3.5-5 mm beyond orifices (1.5-2 mm in diameter) of flat discs (3-4 mm in diameter)
........5 Pedicels 5-12 mm, tomentose, stipitate glandular at least near the base; flowers 1.5-2.5 cm in diameter; hypanthium 2 mm × 1-1.5 mm, eglandular or stipitate-glandular; carpels 6-11, styles glabrous, exserted 3-4 mm beyond the orifice (0.5-1 mm in diameter) of conical discs (2-3 mm in diameter)
....3 Styles distinct or free, usually only the stigmas protruding from the orifice, by 0-4 mm; stipule margins and auricles entire to serrate, not laciniate; shrubs, erect or arching, to 0.3-5 m tall.
..........6 Sepals entire, tapering to apex, persistent on fruit and erect or nearly erect; flowers generally solitary, or with 1-3 laterals.
............ 7 Fruit dark red when ripe, 20-25 mm in diameter; petals 3-5 cm long; pedicel subtended by a clasping bract; [section Cassiorhodon]
............ 7 Fruit blackish when ripe, 8-16 mm in diameter; petals 1-2.5 cm long; pedicel lacking a clasping bract, though often with a modified 3-foliolate leaf; [section Pimpinellifoliae]
..........6 Sepals either lobed or with broadened apices, or if entire then spreading, reflexed, or deciduous from fruit; flowers solitary or corymbose.
............ ..8 Inflorescence of a solitary flower (rarely with a few laterals), the paired bracts on the pedicel caducous; [section Gallicae].
............ ....9 Leaves not glandular-ciliate (or only remotely so); leaves not rugose
............ ..8 Inflorescence either corymbose, or of a solitary flower and its pedicel subtended by persistent bracts.
............ ......10 Sepals disparate in size and shape, the outer pinnatifid with leafy segments; orifice of the hypanthium ca. 1 mm in diameter, the styles slightly exserted; [exotics]; [section Caninae].
............ ........11 Stems to 5 m tall, prickles all similar; leaflets abaxially glabrous or rarely pubescent on midveins, eglandular; bracts 6-18 mm × 4-5 mm, glabrous; sepals abaxially eglandular
............ ........11 Stems to 3 m tall, prickles of varying sizes; leaflets abaxially pubescent or tomentose, rarely glabrous, glandular; bracts 13-15 mm × 5-7 mm, tomentose; sepals abaxially densely stipitate-glandular.
............ ..........12 Stipules 10-16 (-20) mm × 3-4 mm, margins densely glandular-ciliate; leaflet blades 15-30 (-60) mm × 8-22 (-50) mm, abaxial surfaces tomentose; glands of the leaves resin-scented; bracts persistent, tomentose, margins ciliate-glandular; pedicels (11-) 20-35 mm long, densely stipitate-glandular; flowers 3.5-5 cm in diameter; hips dark red, 10-15 mm × 10-12 mm, sepals caducous before hips mature
............ ..........12 Stipules 6-10 mm × 2-4 mm, margins mostly stipitate-glandular; leaflet blades 10-22 mm × 8-15 mm, abaxial surfaces glabrous or pubescent; glands of the leaves apple-scented; bracts caducous, glabrous, margins stipitate-glandular; pedicels 6-9 mm long, densely stipitate- or setose-glandular; flowers 2.5-4 cm in diameter; hips red, 10-25 mm × 10-22 mm, sepals subpersistent.
............ ............ 13 Upper branches with prickles of uniform length and no hairs or bristles; hips 10-12 mm long, 7-9 mm in diameter; sepals deciduous before or as the hip matures; styles usually glabrous; stylar orifices 2.5-4 mm in diameter (1/6-1/5 the diameter of the rim)
............ ............ 13 Upper branches with prickles of variable length and hairs or bristles present or absent; hips 10-25 mm long mm long, 10-22 mm in diameter; sepals deciduous as or after the hip matures; styles usually villous; stylar orifices ca. 4 mm in diameter (ca. 1/3 the diameter of the rim)
............ ......10 Sepals alike, all entire or with a few scarcely leafy teeth near the base; orifice of the hypanthium ca. 2-4 mm in diameter, the opening blocked by the stigmas; [natives and exotics]; [section Cinnamomeae].
............ ............ ..14 Petals 10 or more (flowers ‘doubled’); [exotic]
............ ............ ..14 Petals 5; [native to North America (some populations may be locally introduced)].
............ ............ ......16 Long and straight prickles present throughout the stems
............ ............ ......16 Prickles absent from the stems, or present and short or curved.
............ ............ ........17 Lower leaf surface with generally < 2 hairs per mm²; infrastipular prickles always absent on new stems; bristles always present on new stems; leaflets 7-9
............ ............ ........17 Lower leaf surface with generally >2 hairs per mm²; infrastipular prickles present or absent on new stems; bristles generally absent on new stems; leaflets 5-7
............ ............ ..........18 Bristles present on new branches.
............ ............ ............ ..20 Fertile branches armed with straight, thin or rarely stout, circular or somewhat flattened infrastipular prickles, lacking internodal prickles or aciculi (or if these present , few and scattered); stems mostly thin, pendent or upright; hypanthia (later hips) and pedicels stipitate-glandular (rarely eglandular)
............ ............ ............ ..20 Fertile branches armed with straight, thin or often stout, circular or flattened infrastipular prickles, with internodal prickles of small prickles, aciculi, or stipitate glands, usually densely covering branches and adjacent stems; stems mostly thick, or upright; hypanthia (later hips) and pedicels stipitate-glandular or eglandular
............ ............ ..........18 Bristles absent on new branches.
............ ............ ............ ....21 Leaflets 3.5-5× as long as wide; leaves with (5-) 7-9 (-11) leaflets; petals white; [c. MS westward]
............ ............ ............ ....21 Leaflets 1-3× as long as wide; leaves with (3-) 5-7 (-9) leaflets; petals pink; [collectively widespread].
............ ............ ............ ......22 Hypanthium typically with > 86 glands; terminal leaflet oblong, generally with 20-30 small teeth per side
............ ............ ............ ......22 Hypanthium typically with < 86 glands; terminal leaflet ovate, elliptic, or obovate, with 10-18 (-23) small teeth per side.
............ ............ ............ ........23 Bristles absent on new stems (except in ssp. minidentata, from NY northwards); auricles > 3.8 mm long; stipules > 1.1 mm wide; infrastipular prickles stout, broad-based, and often curved
............ ............ ............ ..........24 Lower stems and branches densely setigerous with aciculi and usually stipitate glands; teeth of leaflets small and ca. 12/cm of margin; [Long Island, NY northwards]
............ ............ ............ ..........24 Lower stems and branches not setigerous; teeth of leaflets larger, < 12/cm of margin; [VA and OH northwards]
............ ............ ............ ........23 Bristles present or absent on new stems; auricles < 3.8 mm long; stipules < 1.1 mm wide; infrastipular prickles slender and not especially broad-based or curved.
............ ............ ............ ............ 25 Fertile branches armed with straight, thin or rarely stout, circular or somewhat flattened infrastipular prickles, lacking internodal prickles or aciculi (or if these present , few and scattered); stems mostly thin, pendent or upright; hypanthia (later hips) and pedicels stipitate-glandular (rarely eglandular)
............ ............ ............ ............ 25 Fertile branches armed with straight, thin or often stout, circular or flattened infrastipular prickles, with internodal prickles of small prickles, aciculi, or stipitate glands, usually densely covering branches and adjacent stems; stems mostly thick, upright; hypanthia (later hips) and pedicels stipitate-glandular or eglandular
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