A key to the species of Keetia (Rubiaceae - Vanguerieae) in West Africa, with three new, threatened species from Guinea and Ivory Coast - Cheek, Martin; Magassouba, Sekou; Molmou, Denise; Doré, Tokpa Seny; Couch, Charlotte; Yasuda, Shigeo; Gore, Charlie; Guest, Amy; Grall, Aurelie; Larridon, Isabel; Bousquet, Isabelle H.; Ganatra, Bella; et al. (Kew Bulletin, 2018)