How to Identify Locust Trees: Key Features and Tips

Locust trees are common in many landscapes and natural areas, valued for their hard wood and attractive foliage. Identifying locust trees accurately can help you appreciate their role in the environment, manage them properly if they grow on your property, or distinguish them from similar species. This guide will walk you through the key characteristics of locust trees, focusing mainly on the two most common types: black locust (Robinia pseudoacacia) and honey locust (Gleditsia triacanthos). No special equipment is necessary, though having a hand lens or smartphone camera can help you examine details closely.

What You’ll Need

• Access to the tree you want to identify (outdoors or in a park)
• Optional: Hand lens or magnifying glass for close-up leaf and bark inspection
• Optional: Smartphone or camera to photograph features for later comparison

Step-by-Step

1. Observe the overall size and shape of the tree. Black locusts typically grow 40-70 feet tall with a rounded or irregular crown, while honey locusts can reach 30-70 feet with a more spreading, open canopy.
2. Examine the bark texture and color. Black locust bark is deeply furrowed, dark brown to black, with thick, rough ridges. Honey locust bark is thinner, gray to brown, and often has vertical fissures but is less rugged than black locust.
3. Look for thorns on the trunk and branches. Black locust trees often have short, paired thorns on young branches and sometimes on the trunk. Honey locusts can have long, branched thorns on trunk and branches, though thornless cultivars are common.
4. Inspect the leaves closely. Both species have compound leaves, but with differences:
   • Black locust: Pinnately compound leaves with 7-19 oval leaflets, smooth edges, about 1-2 inches long.
   • Honey locust: Usually bipinnately compound leaves with many small leaflets (20-30 or more per leaf), giving a feathery appearance.
5. Check for flowers if in season (spring to early summer). Black locust produces fragrant, white, pea-like flowers in hanging clusters 4-8 inches long. Honey locust flowers are smaller, less showy, greenish-yellow, and appear in clusters.
6. Look at the seed pods. Black locust pods are flat, brown, and about 2-4 inches long, containing several seeds. Honey locust pods are longer (up to 8 inches), twisted or coiled, dark brown, and contain sticky pulp.
7. Consider the location and habitat. Black locusts are native to the southeastern U.S. but widely naturalized; they prefer well-drained soils and disturbed areas. Honey locusts are native to central U.S. and tolerate a wide range of soils, often found in open woods and prairies.
8. Use a field guide or tree identification app for cross-checking. Compare your observations with reliable references to confirm your identification.

Common Mistakes

• Confusing black and honey locust due to their similar compound leaves; not checking the number and arrangement of leaflets.
• Overlooking thorn presence, especially on younger branches, which is a key distinguishing feature.
• Misidentifying other trees with compound leaves (like ash or mimosa) as locust because of superficial similarities.
• Ignoring seasonal changes; trying to identify based solely on leaves when flowers or pods provide clearer clues.
• Assuming all locust trees have thorns—some honey locust cultivars are thornless, which can confuse identification.

Tips

• Visit the tree multiple times during the growing season to observe flowers, fruits, and changing leaf characteristics.
• Use a hand lens to inspect leaflets and thorn details closely, especially on young growth.
• Take clear photos of bark, leaves, flowers, and seed pods to compare with online databases or field guides later.
• Note the smell of flowers or crushed leaves; black locust flowers have a strong, pleasant fragrance.
• Learn the common look of other local trees with similar leaves to avoid confusion (e.g., ash trees have opposite leaves, locusts have alternate).

Troubleshooting

If you’re having trouble identifying a locust tree, consider these approaches:

• Missing flowers or pods: If it’s not the right season, focus on bark and leaf structure. Return in spring or late summer when flowers or seed pods are more likely.
• Thornless branches confuse you: Check multiple branches and the trunk. Some honey locusts have thornless cultivars, but black locusts almost always have some thorns on young growth.
• Leaves look damaged or atypical: Try to find multiple leaves from different parts of the tree. Insect damage or disease can alter appearance.
• Uncertain between similar species: Use a reputable tree ID app or consult a local arborist or extension service with your photos.
• Tree is young or stunted: Juvenile trees may lack full features; observe over time or compare with mature specimens nearby.

Frequently Asked Questions

What is the difference between black locust and honey locust?

Black locust has pinnate leaves with fewer, larger leaflets and thick, deeply furrowed bark with short paired thorns. Honey locust usually has bipinnate leaves with many small leaflets, lighter bark with branched long thorns, and longer seed pods.

Are locust trees safe to plant in my yard?

Black locust is hardy and fast-growing but can be invasive in some areas. Honey locust is often used as a shade tree. Both can have thorns, so consider thornless varieties if safety is a concern.

How can I tell if a locust tree is mature?

Mature locust trees have fully developed bark ridges, visible flowers or seed pods during their seasons, and a sizable canopy. Young trees have smoother bark and may lack flowers or pods.

Can I identify locust trees by their flowers?

Yes, black locust flowers are fragrant, white, and pea-like, hanging in clusters, while honey locust flowers are smaller, greenish-yellow, and less conspicuous.

Do all locust trees have thorns?

No. Black locusts generally have short paired thorns on young branches, but honey locusts can have long thorns or be thornless, especially cultivated varieties.

How do I distinguish locust leaves from ash tree leaves?

Locust leaves are alternate on the stem, while ash leaves are opposite. Also, locust leaflets tend to be more oval and fewer per leaf than ash leaflets.

By carefully observing these characteristics and following the steps outlined, you can confidently identify locust trees in your area. Whether for gardening, forestry, or nature study, understanding locust species helps you appreciate their ecological and practical roles.

Related

• Pollo alla Griglia: 10 Delicious Ways to Grill Italian Chicken
• Tollymore Forest Park Highlights: What to See and Do
• Fig and Ricotta Stuffed Shells: Recipes and Tips You’ll Love