(2018)  
 
Rosa gymnocarpa Nuttall var. serpentina Ertter & W. H. Lewis, Madroño. 55: 174, fig. 2. 2008.
Gasquet rose
Stems (1–)3–6(–13) dm. Leaves 2–6(–8) × 1.5–3(–4) cm; stipules 5–11 mm; leaflets 5(–7), often bluish green or red-tinged, ± leathery, terminal: petiolule 2–10 mm, blade broadly elliptic to obovate or ovate to nearly orbiculate, 4–20 × 4–20 mm, apex usually broadly obtuse to rounded, sometimes nearly truncate. Pedicels 10–15 mm, eglandular or stipitate-glandular (in same inflorescence). Flowers 2 cm diam.; petals 8–10 × 6–10 mm. Hips irregularly ovoid to elongate-ellipsoid. Achenes 1–4.
Flowering Apr–Jun. Full sun in roadsides, ridges, and other openings in chaparral and stunted forests on ultramafic substrates; of conservation concern; 400–1500(–2300) m; Calif., Oreg.
Variety serpentina is the form that usually occurs in full sun on ultramafic substrates in the Siskiyou Mountains of northwestern California and southwestern Oregon.

(2018)  
 
Rosa nutkana C. Presl subsp. macdougalii (Holzinger) Piper, Contr. U.S. Natl. Herb. 11: 335. 1906.
Macdougal’s or Spalding rose
Rosa macdougalii Holzinger, Bot. Gaz. 21: 36. 1896 (as macdougali); R. nutkana var. hispida Fernald; R. rainierensis G. N. Jones; R. spaldingii Crépin ex Rydberg
Description

(2018)  
 
Rosa minutifolia Engelmann, Bull. Torrey Bot. Club. 9: 97. 1882.
Ensenada or small-leaved rose
Hesperhodos minutifolius (Engelmann) Hurst
Decription

(2018)  
 
Rosa nitida Willdenow, Enum. Pl. 544. 1809.
Red-spined or shining rose, rosier brillant
Description...
Rosa nitida is typical of the eastern Canadian Provincial Element (S. P. McLaughlin 2007) and is often found near or intermixed with R. virginiana. Putative hybrids between R. nitida (2x) and both R. palustris (2x) and R. virginiana (4x) are reported from Nova Scotia and New England. Because the armature of both R. palustris and R. virginiana is predominately or exclusively of infrastipular prickles, hybridity might explain the infrequent occurrences of R. nitida with infrastipular prickles. In a sample of 23 sheets of R. nitida having abundant prickles, two possess infrastipular prickles.

(2018)  
 
Rosa nutkana C. Presl, Abh. Königl. Böhm. Ges. Wiss., ser. 5. 6: 563. 1851.
Description...
A presumed hybrid between subsp. nutkana (6x) and Rosa rugosa (2x) has been reported from Washington state

Rosa nutkana C. Presl subsp. nutkana
Nootka rose
Rosa aleutensis Crépin; R. durandii Crépin; R. nutkana var. muriculata (Greene) G. N. Jones; R. nutkana var. setosa G. N. Jones
Description

(2018)  
 
Rosa nutkana C. Presl subsp. melina (Greene) W. H. Lewis & B. Ertter, Novon. 17: 345. 2007.
Rocky Mountain rose
Rosa melina Greene, Pittonia 4: 10. 1899; R. oreophila Rydberg; R. pandorana Greene; R. underwoodii Rydberg
Description...
Subspecies melina [6x (DNA)] is endemic to high elevations of the Rocky Mountains Biogeographic Province, where it is often associated with Populus tremuloides Michaux. Curved prickles, glandular sepals, and 2- or 3-serrate leaflets help distinguish subsp. melina where it overlaps with subsp. macdougalii in southeastern Idaho and northern Utah. Significant distributional overlap occurs also with Rosa woodsii subsp. manca, which can occur in mixed or adjacent populations. Subspecies melina is generally at higher elevations, flowers somewhat earlier than subsp. manca, and is hexaploid (the latter is diploid).

(2018)  
 
Rosa palustris Marshall, Arbust. Amer. 135. 1785.
Swamp rose, rosier palustre
Rosa floridana Rydberg; R. gemella Willdenow; R. lancifolia Small; R. obtusiuscula Rydberg; R. palustris var. dasistema (Rafinesque) E. J. Palmer & Steyermark
Shrubs, forming thickets. Stems erect, 10–25(–30) dm, sparsely branched; bark reddish brown, glabrous; infrastipular prickles paired, curved, rarely erect, stout, 3.5–8 × 2–5(–10) mm, ˂base glabrous˃, internodal prickles and aciculi rare, sometimes absent. Leaves 8–11 cm; stipules ˂narrow˃, 10–22(–35) × 2.5–4 mm, auricles erect, rarely flared, 2.5–4.5(–8) mm, margins serrulate, eglandular or stipitate-glandular, surfaces glabrous, eglandular; petiole and rachis usually with pricklets, puberulent to pubescent, sometimes glabrous, eglandular or sparsely stipitate-glandular; leaflets 5–7, terminal: petiolule 5–10 mm, blade ovate-lanceolate, rarely broadly lanceolate or narrowly elliptic, 23–45 × 10–18 mm, membranous, base cuneate, margins 1–2-serrulate, ˂eglandular˃, teeth 20–30 per side, acute to ± obtuse, eglandular, apex acute to subacute, abaxial surfaces pale green, glabrous or pubescent, eglandular, adaxial green, dull, glabrous. Inflorescences corymbs, (1 or)2–10(–40)-flowered. Pedicels erect, slender, 6–15 mm, glabrous, densely stipitate-glandular; bracts 2, lanceolate, 6–15 × 3–4 mm, ˂margins and central veins pubescent˃, eglandular, surfaces pubescent, eglandular. Flowers 2.5–5 cm diam.; hypanthium cupulate, 2–4 × 2–4 mm, glabrous, sparsely to densely stipitate-glandular, neck absent or 1–3 mm; sepals spreading to reflexed, rarely erect, lanceolate to narrowly ovate-lanceolate, 15–30(–40) × 2–3.5 mm, tip 2.5–3.5 × 0.5–1 mm, margins entire, rarely pinnate, abaxial surfaces glabrous, densely, sometimes sparsely, stipitate-glandular; petals single, pink to deep pink, 14–28 × 13–28 mm; ˂stamens 200˃; carpels 24–50, styles exsert 0.5–1 m beyond stylar orifice (1.5 mm diam.) of hypanthial disc (3.5–4.5 mm diam.). Hips deep red, usually globose to subglobose, rarely elongate, 7–11 × 7–11 mm, fleshy, glabrous, sparsely or densely stipitate-glandular, neck absent or 3 × 1 mm; sepals deciduous, spreading. Achenes basal, 26, tan, 3 × 1.5–2 mm. 2n = 14.
Flowering (Jun–)Jul(–Aug). Swampy woods and pastures, marshes, edges of ponds, springs, lakes, backwaters, sloughs, streams, ditches; 0–700 m; N.B., N.S., Ont., Que.; Ala., Ark., Conn., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Ky., Maine, Md., Mass., Mich., Miss., Mo., N.H., N.J., N.Y., N.C., Ohio, Pa., R.I., S.C., Tenn., Vt., Va., W.Va., Wis.; introduced in Europe.
The single 1952 collection of Rosa palustris from Lake of Three Fires State Park (ISC), Taylor County, southwestern Iowa, is about 430 km northwest of the nearest known collection of the species, in Missouri. The species was probably introduced. It has the most serrulate leaflet margins of all roses in North America; the stems usually have short, stout, curved infrastipular prickles, rarely without armature.
Rosa ×palustriformis (Rydberg) Voss (R. carolina var. aculeata Schuette, R. michiganensis Erlanson, R. schuetteana Erlanson) refers to putative hybrids between R. blanda × R. palustris from Maine, Michigan, Ohio, and Wisconsin. Rosa schuetteana is morphologically intermediate between the parental species; R. ×palustriformis is more similar to R. palustris. Rosa blanda and R. palustris differ by: branch armature (R. blanda unarmed or with sparse prickles or aciculi, R. palustris with stout, curved infrastipular prickles or unarmed); length of each auricle (R. blanda average 4.8 mm, R. palustris average 2.6 mm); petioles and rachises with pricklets (R. blanda rare, R. palustris common); leaflet serrations (R. blanda serrate, acute, teeth 10–26 per blade side, R. palustris serrulate, slightly blunt, teeth 20–30 per blade side); pedicels stipitate-glandular (R. blanda eglandular, R. palustris almost always); hypanthia stipitate-glandular (R. blanda eglandular, R. palustris almost always); inflorescences corymbs (R. blanda rare, R. palustris common).
Root decoctions of Rosa palustris were drunk by Cherokee to treat diarrhea (W. H. Lewis and M. P. F. Elvin-Lewis 2003). In Maine, R. palustris hips, including their achenes, are gathered about February, flattened, dried, and ground into flour for use with ground wheat to make leavened bread. The bread has a red color and a fine taste reminiscent of tomatoes (Arthur Haines, pers. comm.).

(2018)  
 
Rosa pinetorum A. Heller, Muhlenbergia. 1: 53. 1904.
Pine rose
Rosa gymnocarpa Nuttall var. pinetorum (A. Heller) Jepson
Description...
Based on pollen size and shape from the type specimen of Rosa pinetorum, E. W. Erlanson (1931) concluded that it is tetraploid (2n = 28). This is consistent with flow cytometry data, which indicated either triploid or tetraploid status (A. Bruneau et al., unpubl.), but not with chromosome counts using the same plant, which clearly showed a diploid 2n = 14 (D. Zlesak and W. H. Lewis, unpubl.).

(2018)  
 
Rosa pisocarpa A. Gray, Proc. Amer. Acad. Arts. 8: 382. 1872.

Rosa pisocarpa A. Gray subsp. pisocarpa
Cluster or pea rose
Rosa rivalis Eastwood
Description

(2018)  
 
Rosa pisocarpa A. Gray subsp. ahartii Ertter & W. H. Lewis, Madroño. 55: 171, fig. 1. 2008.
Ahart's rose
Plants rarely forming thickets. Stems usually solitary or loosely clustered, (2–)4–14(–18) dm; infrastipular prickles 0 or 1(or 2), 2–5 mm. Leaves (5–)6–11(–13) cm; leaflets 5–7, most commonly 5, terminal blade 20–45(–60) mm. Inflorescences 1–3(–10+)-flowered. Flowers: sepal tip to 7 mm, abaxial surfaces usually eglandular, rarely stipitate-glandular; carpels 32–34. Hips subglobose to ovoid, 8–13 mm diam., gradually to abruptly narrowed to neck 2.5–3.5 mm diam. Achenes 5–20. 2n = 28.
Flowering Jun–Aug. Streamsides, meadow margins, roadsides in woodlands, seasonally moist areas in openings of midmontane forests; 100–1700 m; Calif., Oreg.
Subspecies ahartii comprises populations from the northern Sierra Nevada and southern Cascade Range (B. Ertter and W. H. Lewis 2008). Stems tend to have relatively few (or no) prickles, relatively large ovate leaves, and relatively few flowers.