Key to Native and Naturalized Roses in California

IMPORTANT NOTE: the distinctions between rose species are best understood as broad generalizations, with ample room for overlap, intergradation, and exceptions. See Historical Background and Taxonomic Decision-making for a general overview of the taxonomic challenges presented by roses. Note also that prickles are best observed on middle and upper parts of the stem; prickles at the base of the plant are often significantly denser, straighter, and/or thicker than described here.

1. Leaflets < 1 cm long, incised ± halfway to midvein; hips densely bristly; distinctive native of chaparral in extreme southern California and Baja California . . . Rosa minutifolia [subg. Hesperhodos]

1' Leaflets > 1 cm long, toothed < 1/4 to midvein; hips glabrous, hairy, or stalked-glandular [subg. Rosa]

2. Some sepals with perpendicular lateral lobes; styles protruding beyond hypanthial opening; stems generally ± olive-green; prickles strongly curved, thick-based, flattened; petals pink or white; non-natives in pastureland, etc.

3. Stipules fringed; styles few, ± fused, protruding 1.5--3 mm; petals mostly 1--1.5 cm long; flowers many . . . Rosa multiflora Thunb. [sect. Synstylae]

3. Stipules not fringed; styles many, brush-like, only protruding ca. 1 mm; petals 1--2.5 cm long; flowers few [Sect. Caninae]

4. Leaves and sepals glandless, not fragrant; terminal leaflet ± ovate . . . R. canina L.

4' Leaves and sepals glandular, fragrant; terminal leaflet generally elliptic to ± widely obovate . . . R. eglanteria L.

2' Sepals without prominent lateral lobes; styles not protruding, hypanthial opening filled with brushlike stigmas; stem generally ± grayish or brownish; prickles curved to straight, thick-based to slender; petals always pink (except for possible albinos); native species

5. Sepals and neck of hip cleanly detaching at fruit maturity; flowering hip small, generally only 2--3 mm wide; pedicel with prominent stalked glands (except often in Siskiyou Mountains), 1.5--3 cm long; flowers solitary or few; petals ± 10 mm long; pistils < 10; leaflets glabrous, double-toothed, often 4 per side; prickles slender, straight . . . Rosa gymnocarpa [Sect. Gymnocarpae p.p.]

5' Sepals persistent or only irregularly breaking off; flowering hip generally 3--7 mm wide; pedicel various (glabrous, hairy, or glandular), 0.5--3 cm wide; flowers solitary to several; petals generally 10--25 mm long; pistils generally > 10; leaflets variable, rarely more than 3 per side; prickles variable

6. Dwarf ± rhizomatous shrubs, often < 3 dm tall, rarely > 10 dm; leaflet-margins generally double-toothed, glandular; leaflet-apex often ± truncate; prickles straight [Sect. Gymnocarpae p.p.]

7. Hip with generally abundant stalked glands; prickles on stem often abundant, sometimes sparse, generally ± slender (except sometimes in San Luis Obispo Co.); flowers generally 2--5; Coast Ranges and Siskiyou Mountains of California and Oregon . . . Rosa spithamea

7' Hip generally glabrous, rarely with a few stalked glands at base; other features variable

8. Prickles few, paired at nodes, moderately slender; terminal leaflet generally widely obovate; flowers often solitary(--5); Sierra Nevada and Cascade Mountains of California and Oregon . . . Rosa bridgesii

8' Prickles generally abundant, both slender and thick-based intermixed; terminal leaflet generally ± elliptic; flowers general several; native stands of Monterey pine on central California coast . . . Rosa pinetorum

6' Open shrubs or thickets, generally > 5 dm tall, often > 10 dm; leaflet-margins single- or double-toothed, glandless or glandular; leaflet-apex not truncate; prickles variable [Sect. Cinnamomeae]

9. Prickles ± slender (except sometimes in southern California), straight or slightly curved, sparse to abundant; leaves and sepals glandless; hypanthium glabrous; flowers 1--5(10); mountains of southern California, including Mojave Desert, north mostly on the east side of the Sierra Nevada crest . . . Rosa woodsii var. ultramontana

9' Prickles generally ± thick-based and flattened, otherwise variable; other features variable; west side of the Sierra Nevada

10. Prickles generally strongly curved and flattened, generally few, not strongly contrasting with stem; pedicels generally ± hairy; hip sometimes hairy, most often ± ovoid; sepals often without glands, the tip generally no longer than sepal-body . . . Rosa californica

10' Prickles generally not curved, often only moderately flattened, few to many, often pale and contrasting with dark stem; pedicels glabrous to glandular but not hairy; hip glabrous or glandular but not hairy, most often globose; sepals generally with glands, the tip prominent, generally > sepal-body

11. Hip generally 5--7 mm wide at flowering, 10--15 mm wide at maturity; flowers most often solitary (to 4), relatively large; leaflets, pedicels, and hips sometimes glandular; prickles often abundant, especially near coast; most common in coastal marshes, but extending inland in a less prickly form . . . Rosa nutkana

11' Hip generally 3--6 mm wide at flowering, ± 10 mm wide at maturity; flowers generally clustered, 2--10; sepal-tips not toothed; leaflets, pedicels, and hips never glandular; prickles mostly paired at nodes, sometimes nearly absent; northwestern California . . . Rosa pisocarpa

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