Thorns on a flowering tree provide protection from animals that may be searching for fresh leaves or fruits to eat. When using flowering trees that bear such armament in the garden, carefully consider the tree's mature size and shape and plant it so its branches do not pose a hazard to humans. Avoid planting thorned trees around playgrounds or too near to high pedestrian traffic around patios or sidewalks.
Hawthorns (Crataegus spp.) make nice, small flowering trees in temperate climates. Typically thousands of small white flowers load the thorned branches in spring as the new leaves emerge, followed by tiny orange to red berries by summer's end. Some species' flowers bear a musky, unpleasant odor. Some of the more commonly encountered species include the cockspur hawthorn (Crategus crusgalli), English hawthorn (Craetagus laevigata), Lavalle hawthorn (Crataegus x lavallei), glossy hawthorn (Crataegus nitida), Washington hawthorn (Crataegus phaenophyrum), thicket hawthorn (Crataegus punctata) and the green hawthorn (Crataegus viridis).
Warm, or cool but mild winter regions with dry soils often find the Mexican palo verde or Jerusalem thorn (Parkinsonia aculeata) grows as a small, spring-flowering tree. Wispy leaflets make it look like a broom, but the numerous golden yellow flowers in spring reveal a welcome fragrance. The floppy branches with thorns can be problematic near walkways if not seasonally trimmed. Other closely related palo verde trees, which also bloom and bear thorny stems, include the blue palo verde (Parkinsonia florida) and the foothills palo verde (Parkinsonia microphylla). Some of these trees used to be classified as Cercidium rather than Parkinsonia species.
Coral trees bear fiery orange-to-red flowers in late winter through summer, depending on species. Their leaves bear three leaflets and the branches, particularly ones younger than a couple years old are lined in thorns. Particularly showy coral trees include the coast coral tree (Erythrina caffra), cockspur coral tree (Erythrina crista-galli) and the Indian coral tree (Erythrina variegata).
The Brazilian potato tree (Solanum wrightii) blooms year-round in tropical regions with stems hiding tiny curving thorns. There even are prickles on the leaf blades.
A general, ambiguous name for trees in the botanical genus Caesalpinia, dwarf poinciana trees bear yellow-to-red flowers in summer with long stamens that look like whiskers. Thorns are camouflaged in the stems between leaves in two species common in tropical gardens: pride-of-Barbados (Caesalpinia pulcherrima) and peachwood (Caesalpinia echinata).