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Rosa

Most of the cultivated roses, which seldom escape, are “double,” i.e., some or all of the stamens are converted into extra petals. Our native wild roses are “single,” with 5 petals, usually pink but sometimes a deep purplish and rarely albino. Following widespread usage, the floral tube, which ripens into the fruit, a bright red or orange ± fleshy “hip,” is here termed the hypanthium; it closely resembles an inferior ovary from a superficial external view. The calyx lobes are then simply termed sepals; these are ± pinnately lobed or pinnatifid in many of the cultivated species and also frequently in several of our native ones.

Rosa damascena Mill. was collected by Farwell (No. 7415) in Wayne Co., and reported by him (Am. Midl. Nat. 10: 33. 1926) as “Near the cellar remains of an old residence at Nankin. Probably once cultivated but now persistent.” There is no evidence that this was spreading beyond where it was planted. It would key here perhaps best to Rosa gallica, from which it differs in having only the young stems, peduncles, and hypanthium strongly stalked-glandular, with the stipules, petioles, and leaf rachis glandless or only sparsely glandular. Rosa gallica has stipules, petioles, leaf rachis, and even midveins of the leaflets (though not the leaf undersurface) conspicuously glandular. 

Some Rosa sp., especially R. multiflora, have long arching canes that may scramble through shrubs and occasionally into the lower branches of small trees in thickets. These are sometimes called "climbing roses" but as their habit is mostly that of shrubs, they are here considered shrubs rather than vines.

 

1. Sepals (3 outer ones) pinnatifid or at least with narrow lateral lobes; local escapes from cultivation (except for 3 native species keyed here as well as under the alternative because they often have lobed sepals).

2. Inflorescence several to many-flowered; styles glabrous; stipules deeply pinnatifid.

R. multiflora

2. Inflorescence 1–4-flowered (rarely more); styles villous; stipules entire (or with stalked glands on the margins).

3. Leaflets on most if not all leaves 9–11; pedicels and hypanthium smooth and glabrous.

R. arkansana (in part)

3. Leaflets 5–7; pedicels and usually hypanthium ± glandular-hispid (except in R. canina).

4. Flowers densely double, ± nodding.

R. centifolia

4. Flowers usually single, not nodding.

5. Petals less than 2 cm long; stalked glands more conspicuous than the pubescence on lower surface of leaflets and ± dense on pedicels, sepals, and stipules.

R. rubiginosa

5. Petals usually longer than 2 cm; stalked glands absent or less conspicuous than dense pubescence on lower surface of leaflets, and absent to dense elsewhere.

6. Leaflets densely pubescent beneath and also glandular; mature fruit ca. 12–18 mm in diameter.

R. villosa

6. Leaflets (except on midvein) glabrous or sparsely pubescent and glandular beneath, the leaf surface clearly visible; mature fruit less than 12 mm in diameter.

7. Leaflets sparsely pubescent beneath; young stems with stalked glands.

R. gallica

7. Leaflets essentially glabrous beneath; young stems without stalked glands.

8. Pedicels and hypanthium glabrous; uncommon alien species with long, arching canes.

R. canina

8. Pedicels and hypanthium glandular-hispid; species with upright stem, native except for R. virginiana.

9. Leaflets with ± 20 or more fine teeth on a side; nodal prickles stout, down-curved; wet habitats.

R. palustris (in part)

9. Leaflets with ± 15 or fewer primary teeth on a side (sometimes doubly serrate); nodal prickles stout or slender, straight (or ± down-curved in the rare introduction R. virginiana); dry habitats.

10. Nodal prickles usually slender, not clearly reflexed, internodal prickles present and similar to nodal ones in form if not size.

R. carolina (in part)

10. Nodal prickles stout, expanded and flattened near the base, reflexed; internodal prickles usually absent.

R. virginiana (in part)

1. Sepals entire; escaped or native species (all native species are included here).

11. Styles glabrous, united into a single column (stigmas ± separate) protruding from the hypanthium nearly or quite as far as the stamens; leaflets only 3 (–5) on fertile shoots.

R. setigera

11. Styles villous, separate but forming a dense head in the throat of the hypanthium, much shorter than the stamens; leaflets mostly 5–11.

12. Leaflets ± rugose, densely soft-pubescent beneath; young branchlets, prickles, leaf rachises, and pedicels densely pubescent.

R. rugosa

12. Leaflets not rugose, glabrous or lightly pubescent beneath; young branchlets and prickles, and often other parts, glabrous or with stalked glands.

13. Stems with strong, slightly down-curved or reflexed prickles immediately below most branchlets and petioles but few if any other prickles (except sometimes at base of plant).

14. Pedicels and hypanthia smooth, glabrous; sepals erect on the mature fruit; rare escapes from cultivation along roadsides and fields.

R. cinnamomea

14. Pedicels and hypanthia glandular-hispid; sepals widely spreading on mature fruit.

15. Leaflets with ± 20 or more fine teeth on a side; wet habitats.

R. palustris (in part)

15. Leaflets with ± 15 or fewer teeth on a side; dry habitats.

R. virginiana (in part)

13. Stems with prickles, if any, below the nodes straight and internodal prickles often of similar size and shape.

16. Leaflets mostly 6–12 mm long, glabrous beneath; flowers solitary; stems ± well armed with slender broad-based prickles and more slender needle-like prickles; uncommon escapes from cultivation.

R. spinosissima

16. Leaflets mostly ca. (15–) 18 mm or more long, usually pubescent at least on midvein beneath; flowers 1–several in an inflorescence; stems variously smooth or armed; native shrubs.

17. Pedicels and hypanthia glandular-hispid; sepals ± widely spreading and usually deciduous from mature fruit; native species in dry ground in southern Lower Peninsula, with straight narrowly tapered prickles, especially below the nodes [hybrids of R. blanda × R. palustris with glandular hypanthia would also run here; see text].

R. carolina (in part)

17. Pedicels and hypanthia smooth and glabrous; sepals ± erect and persistent on fruit; various distributions and habitats.

18. Leaflets (7–) 9–11, usually ± soft-pubescent beneath and obovate; flowers mostly clustered at the ends of long, ± strongly glaucous, at least sparsely prickly new shoots; stipule margins mostly glandless or irregularly glandular.

R. arkansana (in part)

18. Leaflets 5–7 (rarely 9 on vegetative shoots), variously pubescent and shaped (mostly ovate-elliptic if new shoots prickly); flowers mostly on prickly short lateral shoots or on smooth (sometimes glaucous) shoots; stipule margins various.

19. Lateral (floral) branches bristly; leaflets usually doubly serrate, especially toward apex, the primary teeth ovate (biconvex); margins of floral bracts and stipules usually ± copiously glandular.

R. acicularis

19. Lateral branches smooth; leaflets singly serrate, the teeth sharp, often straight or concave on inner side; margins of floral bracts and stipules glandless or sparsely glandular or sometimes copiously glandular.

R. blanda