Taylor et al. (2014) presented a synoptic treatment of this genus in Madagascar, with a key to the species. The record of the Mauritius species G. calycina Bojer from Madagascar is believed to be erroneous (Malcomber & Taylor 2009). Bertiera crinita is frequently confused with Gaertnera, but differs in its inferior ovary and interpetiolar stipules.
Several species are quite similar and share coriaceous leaves with the higher order venation not or hardly visible, tubular stipules, and corymbiform inflorescences with small bracts. These were previously included in Gaertnera obovata var. sphaerocarpa (which has long calyptrate stipules) and Gaertnera macrostipula. The circumsription here of Gaertnera macrostipula is narrowed to include plants with chartaceous leaves with the higher-order venation well developed and well developed inflorescence bracts. These plants are often found in littoral and dry vegetation, and are here various treated in Gaertnera xerophila (leaves thickly coriaceous), Gaertnera breviflora (found in SE and with very short corollas), Gaertnera sclerophylla (similar to Gaertnera breviflora and partly sympatric but with flowers twice as long or longer), Gaertnera robusta (found in E and with well developed lobed calyx limb), Gaertnera razakamalalana (found in E and similar to Gaertnera sclerophylla but with inflated stipules, rounded leaf apices, and very short peduncles), and Gaertnera nitida (found in N and with shortly acuminate, generally smaller leaves).