Alnus tenuifolia (al’-nus ten-ewe-i-fo’-lee-a)
Family: Betulaceae, Birch

Key Steps

• 1b – Alternate leaf arrangement — go to 18
  • 18a – Leaf simple — go to 19
    • 19b – Thornless — go to 22
      • 22d – All leaves lobed — go to 23
        • 23a – Pinnate venation — go to 24
          • 24b – Leaves not clustered toward stem tip. Pith not 5-angled — go to 29
            • 29d – Lobes are coarsely serrated. Brown bark. Triangular pith. Female catkin appears as a woody “cone”; male catkin is papery — Thinleaf Alder

Description

Leaf: Coarsely, double-toothed, broad, round tip, wedged base, 6-8 pairs of veins. Tufts of hair in veins axils beneath. Hairy stipules, 1/2 inch long. Orange-colored central vein beneath. Stout, grooved petiole, 1 inch long.

Bud: Stalked, 1/3″ long, bright red, a little hairy. Two or more scales, barely meeting. True terminal bud absent.

Leaf Scar: Half round, raised

Stem: Slender, not peeling. Tight bark. Young: rusty, hairy. No wintergreen or spicy taste or odor.

Bark: Smooth, becoming scaly with age. Light brown to gray.

Pith: Triangular in cross section.

Flower: Female: egg-shaped strobile before leaves. Male: 2-4 inch long catkin, 3-5 clustered together.

Fruit: Persistent woody strobile, looks like a miniature cone. Less than 1 inch long.

Habit: Birch-like, slender. May be multi-stemmed. To 15 feet tall, upright, clump forming.

Culture: High water needed; use in moist sites. Alders fix nitrogen in the soil, similar to legumes.

Resources

• Identifying Broadleaf Flowering Trees and Shrubs, CMG GardenNotes #173
• List of trees in this key
• Glossary of Terms
• Front Range Tree Recommendation List
• Online CSU Extension publications on Tree and Shrub Selection