Flora of North America species comparison

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Frangula alnus

Frangula

alder buckthorn, columnar buckthorn, European alder, European alder-buckthorn, fen buckthorn, glossy buckthorn, glossy false buckthorn, tall hedge buckthorn

buckthorn, coffee berry
Habit Shrubs or small trees, 2–5(–7) m. Stems greenish to brown, sparsely puberulent, glabrescent. Shrubs or trees, unarmed; bud scales absent, buds hairy.
Leaves

deciduous;

petiole 10–19 mm;

blade dull green abaxially, glossy darker green adaxially, broadly elliptic-obovate to broadly elliptic or broadly oblong, 4–7(–11) cm, herbaceous, base cuneate to rounded, margins entire, apex rounded to acute or abruptly short-acuminate, abaxial surface sometimes minutely strigose along midveins, adaxial surface glabrous;

secondary veins 6–10 pairs.

usually deciduous, sometimes persistent, alternate [rarely opposite], rarely fascicled on short shoots;

blade not gland-dotted; pinnately veined, secondary veins nearly straight, parallel.
Inflorescences

fascicles, sessile, 1–8-flowered.

axillary, within foliage, umbels or fascicles, or flowers solitary;

peduncles and pedicels not fleshy in fruit.
Pedicels

3–10 mm.

present.
Flowers

bisexual;

hypanthium cup-shaped, 1–3 mm wide, usually circumscissile far below sepal bases, rarely not circumscissile;

sepals (rarely 4–)5, usually ± erect, sometimes spreading, yellowish to green or white, ovate-triangular, fleshy, keeled adaxially;

petals (rarely 4–)5, yellowish, hooded, broadly obovate to obcordate, clawed;

nectary thin, lining hypanthium;

stamens (rarely 4–)5;

ovary superior, (2–)3-locular;

style 1.
Fruits

drupes;

stones 2–3(–4), indehiscent but open at base.
Drupes

black, globose or slightly elongate, 6–8 mm;

stones 2(–3).

Seeds

obovoid to lenticular, with cartilaginous beak protruding through opening in stone, not furrowed.
Stigmas

2–3-lobed.

x

= 20–26.
2n

= 20–26.

Frangula alnus

Frangula
Phenology Flowering May–Sep.
Habitat Alkaline and acid tamarack, red maple and cedar swamps, peatlands, bogs, fens, disturbed areas, riparian thickets, lakeshores, ditches, fencerows, hedgerows, low woods, beaver meadows.
Elevation 10–400 m. (0–1300 ft.)
Distribution
from FNA
CO; CT; IA; ID; IL; IN; KY; MA; ME; MI; MN; NE; NH; NJ; NY; OH; PA; RI; TN; VT; WI; WV; WY; MB; NB; NS; ON; PE; QC; SK; Europe [Introduced in North America; introduced also in Asia (China, Russia), n Africa]
[WildflowerSearch map]
[BONAP county map]
from USDA
North America; Mexico; Central America; South America; West Indies; Europe; e Asia; n Africa
[BONAP county map]
Discussion

Two horticultural forms of Frangula alnus are widely sold and planted in North America. The cultivar 'Asplenifolia' (F. alnus var. asplenifolia Dippel; fern leaf or cutleaf buckthorn) has linear-oblong leaves with coarsely toothed to incised margins and commonly is grown as a specialty plant. The cultivar 'Columnaris' (tallhedge glossy buckthorn) has a narrow, upright habit and is used in hedging. Both forms were noted by M. H. Brand (http://www.hort.uconn.edu/plants/r/rhafra/rhafra1.html) to spread invasively by seeds. 'Asplenifolia' has been reported as naturalized in Ontario (A. W. Dugal 1989, 1992), Illinois (A. Branhagen, pers. comm.), and Ohio (M. K. Delong et al. 2005).

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Species ca. 50 (7 in the flora).

The difference between Frangula and Rhamnus has long been recognized, but treatments in taxonomic rank have been inconsistent. Frangula was treated within Rhamnus by M. C. Johnston and L. A. Johnston (1978), who noted that Frangula and Rhamnus are more closely related to each other than to other taxa. This observation has been corroborated by molecular studies that show them as sister taxa (J. E. Richardson et al. 2000; K. Bolmgren and B. Oxelman 2004). Frangula was also included within Rhamnus by D. Medan and C. Schirarend (2004) and by Chen Y. L. and C. Schirarend (2007), but various other recent treatments, as here, have maintained them as separate genera, emphasizing the differences outlined above in couplet 13 of the key to genera.

The key to species emphasizes geography as a primary character, reflecting the close similarities among the species and allowing morphological contrasts between sympatric taxa.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Key
1. Leaves persistent, semideciduous, or deciduous, blades distinctly coriaceous.
→ 2
2. Leaves persistent; drupes 10–15 mm.
F. californica
2. Leaves semideciduous or deciduous; drupes 5–10 mm.
→ 3
3. Leaf blades glaucous adaxially when fresh; Plumas County, California.
F. purshiana
3. Leaf blades not glaucous adaxially; Arizona, Colorado, Nevada, Utah.
F. obovata
1. Leaves deciduous, blades herbaceous to subcoriaceous.
→ 4
4. Eastern North America, as far west as Manitoba, Nebraska, and central Texas.
→ 5
5. Inflorescences umbels, pedunculate; drupes 8–10 mm; leaf blades oblong to elliptic or obovate-elliptic, margins serrulate to crenulate to nearly entire; drupe stones 3.
F. caroliniana
5. Inflorescences fascicles, sessile; drupes 6–8 mm; leaf blades broadly elliptic-obovate to broadly elliptic or broadly oblong, margins entire; drupe stones 2(–3).
F. alnus
4. Western North America, as far east as Colorado, New Mexico, trans-Pecos Texas, and Wyoming.
→ 6
6. Inflorescences fascicles, sessile.
F. alnus
6. Inflorescences umbels, pedunculate.
→ 7
7. British Columbia, California, Idaho, Montana, w Nevada, Oregon, Washington.
→ 8
8. Leaf blades 1.5–8.5 cm; drupe stones 2(–3); inflorescences (2–)4–15-flowered; California, Nevada, Oregon.
F. rubra
8. Leaf blades 6–15 cm; drupes stones 3; inflorescences 10–25-flowered; British Columbia; California, Idaho, Montana, Nevada, Oregon, Washington.
F. purshiana
7. Arizona, Colorado, s Nevada, New Mexico, Texas, Utah.
→ 9
9. Leaf blades elliptic to oblong, elliptic-ovate, or narrowly ovate, 1.6–2.6(–2.9) times longer than wide, ± herbaceous, secondary veins (8–)9–13 pairs; se Arizona, New Mexico, Texas.
F. betulifolia
9. Leaf blades obovate to oblong-obovate or oblong, 1.2–1.8(–2.5) times longer than wide, subcoriaceous, secondary veins (5–)6–8(–9) pairs; n Arizona, Colorado, Nevada, Utah.
F. obovata
Source FNA vol. 12, p. 59. FNA vol. 12, p. 52. Authors: John O. Sawyer†, Guy L. Nesom.
Parent taxa Rhamnaceae > Frangula Rhamnaceae
Sibling taxa
F. betulifolia, F. californica, F. caroliniana, F. obovata, F. purshiana, F. rubra
Subordinate taxa
F. alnus, F. betulifolia, F. californica, F. caroliniana, F. obovata, F. purshiana, F. rubra
Synonyms Rhamnus frangula Rhamnus section frangula, Rhamnus subg. frangula
Name authority Miller: Gard. Dict. ed. 8, Frangula no. 1. (1768) Miller: Gard. Dict. Abr. ed. 4, vol. 1. (1754)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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