They might be cucumbertree (Magnolia acuminata). This magnolia flowers in late spring to early summer, but the flowers are nondescript green and not particularly showy. They are also borne high in the tree and are often masked by foliage. This species also doesn't flower until the tree grows to at least 20 feet in height. Leaves are dark green above and lighter green and slightly hairy on their undersides. They may be up to 10 inches long.