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Rosa

See list of 21 species in this genus

Prickle stature and density are important characters for Rosa identification. They must be assessed on normal shoots. Plants sometimes produce vigorous shoots with greatly elongated growth (identifiable by the absence of both abrupt color changes of the bark and annual scars normally found at the junction of year’s growth). These vigorous shoots are usually much more densely prickly than the normal shoots and are misleading for identification. Stipule morphology is also very important and should not be assessed on the apical-most one or two leaves, as these are sometimes different from those near the base and middle of the branchlet. Peduncle and pedicel bracts are frequently caducous and often are shed soon after flowering. They are best observed on peduncles supporting budding flowers. Species noted to have pinnatifid sepals actually bear flowers with 2 entire sepals, 2 sepals bearing slender lobes on both margins, and 1 sepal bearing slender lobes on only 1 margin. Many of the cultivated species from Europe that are naturalized in New England normally produce double corollas ( flore pleno; e.g., R. gallica [Fig. 859], R. cinnamomea). References: Lewis (1957), Graham and Primavesi (2005), Joly and Bruneau (2007).

  • 1a. Styles connate (though sometimes becoming distinct, in part, in age), the stigmas conspicuously exserted 3–6 mm from the orifice of the hypanthium and ± equaling the height of the stamens [Fig. 860]; inflorescences (1–) 3- to 30-flowered; stems climbing or scrambling
  • 1b. Styles distinct (though often closely connivent), the stigmas barely to slightly exserted beyond the orifice of the hypanthium (i.e., up to 2 mm) and shorter than the stamens; inflorescences 1- to 6 (–15)-flowered; stems erect to arched
    • 5a. Flowers solitary at the tips of branches (rarely in pairs or trios); peduncle borne from the axil of a leaf but without additional bracts; stems often provided with abundant prickles and bristles (i.e., prickles evidently varying in thickness)
    • 5b. Flowers solitary or 2–6 and arranged in a corymb; peduncle and/or pedicels bracteate [Fig. 861]; stems unarmed or provided with sparse to abundant prickles, when prickles abundant, then of relatively uniform thickness (except in R. rugosa, but then the prickle bases pubescent)
      • 7a. Branchlets, young prickles, and older prickle bases densely tomentose; fruiting hypanthia 20–30 mm wide, borne on outward-curved to down-curved pedicels; petals mostly (30–) 35–50 mm long; leaflets strongly rugose-veiny
      • 7b. Branchlets, young prickles, and older prickle bases glabrous or sparsely pubescent; fruiting hypanthia 7–20 mm wide, borne on straight to weakly curved pedicels (sometimes curved in R. acicularis); petals 9–28 mm long (up to 45 mm long in R. gallica, but that species with pinnatifid sepals); leaflets not or only somewhat rugose-veiny
        • 8a. Orifice of the hypanthium 1–2 mm wide, the stigmas exserted 1–2 mm beyond it (i.e.; the apical portion of the styles visible in intact flowers and fruits); sepals pinnatifid; achenes usually lining the inner wall of the hypanthium as well as the receptacle
          • 9a. Leaflets ± single serrate, lacking marginal stipitate glands and lacking glands on the surfaces; pedicels glabrous
          • 9b. Leaflets double serrate, stipitate-glandular on the margin and on one 
or both surfaces (usually lacking glands on the surfaces in R. gallica); pedicels stipitate-glandular
            • 10a. Pedicels (10–) 20–60 mm long, stout; petals 25–35 (–45) mm long 
 (in part)
            • 10b. Pedicels 6–20 mm long, moderately thick to slender; petals 8–25 mm long
              • 11a. Foliar glands subsessile, when fresh mostly less than 0.05 mm in diameter, brown-red to translucent, and with a resinous odor; leaflets tomentose abaxially (at least along the veins), sparsely tomentose adaxially
              • 11b. Foliar glands evidently stalked, when fresh mostly 0.05–0.1 mm in diameter, translucent, and with a sweet, fruity odor; leaflets pubescent along the major veins abaxially and glabrous to sparsely pubescent adaxially
                • 12a. Styles pubescent; sepals erect-ascending post anthesis, sometimes persisting in fruit; leaflets evidently glandular on the abaxial surface or on both surfaces, very aromatic; prickles of unequal sizes, ranging from acicular to stout; mature hypanthia 10–15 mm wide
                • 12b. Styles glabrous; sepals reflexed post anthesis, deciduous in fruit; leaflets glandular on only the abaxial surface, weakly aromatic; prickles of ± equal size, none of them acicular; mature hypanthia 7–10 mm wide
        • 8b. Orifice of the hypanthium (1.5–) 2–4 mm wide, the stigmas barely exserted beyond it and closing off the opening (i.e., the styles not visible in intact flowers and fruits); sepals entire or with 1–4 linear appendages; achenes confined to the receptacle or also lining the walls of the hypanthium
          • 13a. Pedicels and hypanthium stipitate-glandular [Fig. 861]; sepals spreading or reflexed after anthesis, promptly deciduous in fruit; achenes confined to the receptacle
            • 14a. Leaflets with fine teeth, the teeth near the middle of the leaflet 
(0.3–) 0.4–0.7 mm long; plants of hydric soils
              • 15a. Stems with a pair of stout, broad-based, often curved prickles at most of the nodes, these prickles much larger than the few, slender ones of the internodes; leaflets dull or scarcely lustrous adaxially, the terminal one with (16–) 21–25 (–27) teeth per margin; hypanthium with (40–) 70–98 (–135) stipitate-glands; connate portion of the stipules with ± parallel margins, scarcely widened distally; inflorescence with usually 2 or more flowers
              • 15b. Stems with numerous internodal prickles that are slender, small-based, and straight, similar to the prickles found at the nodes; leaflets lustrous on the adaxial surface, the terminal one with (13–) 14–20 (–23) teeth per margin; hypanthium with (8–) 35–55 (–80) stipitate-glands; connate portion of the stipules without parallel margins, widened distally; inflorescence with usually 1 flower
            • 14b. Leaflets with coarse teeth, the teeth near the middle of the leaflet 
(0.4–) 0.7–0.9 (–1.3) mm long; plants of mesic to xeric soils (infrequently of hydric soils in R. virginiana)
              • 16a. Connate portion of the stipules without parallel margins, widened distally, each wider than 1.1 mm [Fig. 862, L]; nodal prickles usually relatively stout, sometimes curved; internodal prickles usually absent on branchlets; leaflets lustrous adaxially; inflorescence commonly with 3 or more flowers; petioles rarely bristly
              • 16b. Connate portion of the stipules with ± parallel margins, scarcely widened distally, each narrower than 1.1 mm [Fig. 862, R]; nodal prickles usually slender and straight; internodal prickles often present on branchlets; leaflets dull or scarcely lustrous adaxially; inflorescence commonly with 1 or 2 flowers; petioles commonly bristly
          • 13b. Pedicels and hypanthium glabrous (pedicels or both the pedicels and hypanthia stipitate-glandular in rare forms); sepals erect or connivent after anthesis (reflexed in R. blanda var. glabra), persistent in fruit (frequently deciduous at maturation of fruit in R. glauca); achenes usually lining the inner wall of the hypanthium as well as the receptacle
            • 17a. Stems with a pair of stout, broad-based, often curved prickles at most of the nodes [Fig. 858], these prickles much larger than the few slender ones of the internodes; corolla usually double [Fig. 859]
            • 17b. Stems without prickles or with few to numerous prickles, the prickles of the nodes not strongly differentiated from those of the internodes (i.e., all the prickles of ± similar dimension); corolla usually single
              • 18a. Leaflets softly tomentose on both surfaces, abaxially with tiny, red to red-brown, subsessile glands that present a resiny odor when bruised on living plants
              • 18b. Leaflets glabrous to pubescent, but not tomentose on both surfaces, lacking aromatic resin glands (but sometimes with subsessile glands in 
 R. acicularis)
                • 19a. Leaflets glaucous and/or stronged tinged with red to brown-purple, single-serrate on the margin; branchlets glaucous, the bloom usually persisting into fruit
                • 19b. Leaflets green, single or double-serrate on the margin; branchlets without bloom or glaucous only when young
                  • 20a. Leaves with (7–) 9 or 11 leaflets; leaflets obovate to oblong-obovate; inflorescence with (1–) 3 or 4 (–5) flowers, usually borne 
both on lateral branchlets from branches of the previous year and 
on terminal branchlets of the current season
                  • 20b. Leaves with 5 or 7 leaflets; leaflets elliptic or oblong to ovate or obovate; inflorescence with 1 or 2 (–3) flowers, usually borne only on lateral branchlets that are borne on branches of the previous year
                    • 21a. Branchlets with numerous prickles [Fig. 857]; usually the upper stipules, floral bracts, petioles, and/or leaf rachises stipitate-glandular, at least when young; fruiting hypanthium dark blue 
in drying
                    • 21b. Branchlets without prickles (rarely with a few prickles); upper stipules, floral bracts, petioles, and leaf rachises without stipitate glands (though often with sessile glands at the tips of the teeth of the stipules and/or floral bracts); fruiting hypanthium usually red 
to red-brown in drying

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