The Manual of the Botany of the Northern United States / Including the District East of the Mississippi and North of North Carolina and Tennessee

by Asa Gray

[*] Calyx deciduous, without bractlets, pistil solitary, becoming a drupe.

Tribe I. PRUNEÆ. Trees or shrubs, with simple mostly serrate leaves. Ovules 2, pendulous, but seed almost always solitary. Style terminal.

1. Prunus. Flowers perfect. Lobes of calyx and corolla 5. Stone of the drupe bony.

[*][*] Calyx mostly persistent; pistils few to many (rarely solitary).

[+] Calyx without bractlets; ovules 2–many.

Tribe II. SPIRÆEÆ. Pistils mostly 5, becoming 2–several seeded follicles. Shrubs or perennial herbs.

a. Calyx short, 5 cleft. Petals obovate, equal.

2. Spiræa. Flowers perfect or diœcious. Pods 1-valved. Herbs or shrubs; leaves simple or pinnate.

3. Physocarpus. Pods inflated, 2-valved. Shrub; leaves palmately lobed.

b. Calyx elongated, 5-toothed. Petals slender, unequal.