Rosaceae tribe Dryadeae

Plants unarmed. Leaves alternate, simple, sometimes pinnately compound or basal leaflets 1(or 2); stipules deciduous or persistent, free or adnate to petiole; venation pinnate. Flowers: perianth and androecium perigynous; epicalyx bractlets absent; hypanthium saucer-shaped, obconic, funnelform-turbinate, or cylindric; torus absent or hemispheric; carpels 1(or 2) or 4–150, distinct, free, styles terminal, distinct; ovule 1, basal (without obturator). Fruits achenes or aggregated achenes; styles persistent, elongate.

Distribution

North America, Mexico, Eurasia.

Discussion

Genera 4, species 34 (4 genera, 17 species in the flora).

Members of Dryadeae are nitrogen fixing in association with Frankia. Cyanogenic glycosides are present, and sorbitol is present in trace amounts. The base chromosome number for the tribe is x = 9 (D. Potter et al. 2007). Dryadeae is probably North American in origin.

The obturator is a placental (or funicular) outgrowth present at the micropylar end, which directs the passage of pollen tubes towards the ovule.

Selected References

None.

Lower Taxa

Cercocarpus, Chamaebatia, Dryas, Purshia

Key

1	Leaves 2–3-odd-pinnately compound; inflorescences (1–)2–7(–10)-flowered, corymbs or panicles.	Chamaebatia
1	Leaves simple or with 1(–2) basal leaflets, (margins lobed, toothed, or entire); inflorescences 1–3(–18)-flowered clusters or flowers solitary	> 2
2	Petals 0; hypanthia narrowly cylindric; carpels 1(or 2); achenes solitary.	Cercocarpus
2	Petals 5–10(–12); hypanthia saucer-shaped or obconic; carpels 1–31 or 60–150; achenes usually aggregated, sometimes solitary (Purshia)	> 3
3	Shrubs 0.1–2.3 dm; hypanthia saucer-shaped; petals 8–10(–12).	Dryas
3	Shrubs 2–75 dm; hypanthia obconic; petals 5.	Purshia