Black locust, mulberry, and osage are similar in that they have a thin band of sapwood, and much heartwood. They're all decent bow wood, osage being the best imo. Once cut and reduced to heartwood, locust and mulberry especially, can be confused for one another. But one distinct characteristic of black locust is that it's fluorescent under a black light. It glows like it's radioactive... especially when freshly exposed with a cutting tool.