Exotesta morphology of the Gardenieae — Gardeniinae (Rubiaceae)

Persson, C. 1995. Exotesta morphology of the Gardenieae-Gardeniinae (Rubiaceae). -Nord. J. Bot. 15: 285–300. CGpenhagen. ISSN 0107–055X.
Exotesta morphology of 68 species in 59 genera of the Gardeniinae were examined with the aid of scanning and light microscopy. The shape of the exotesta cells in surface is either isodiametrical or elongate and both shapes occur among New World and Old World genera. All genera, except for Monosalpinx, Posoqueria and Macrosphyra , are provided with secondary thickenings in the cell walls of the exotesta. The majority of the genera has a thickened radial wall. In the Asian genera Catunaregam, Deccania, Tamilnadia and the mainly Pacific genera, Atractocarpus and Trukia thickenings of the radial wall are very low or absent. In nearly half the genera the inner tangential wall is provided with thickenings, usually in the shape of a continuous plate. However, in four African genera, Atractogyne, Didymosalpinx, Mitriostigma and Sherbournia , the wall is provided with elongate anastomosing ribs. Atractocarpus differs markedly from the rest of the Gardeniinae by its ring-like thickenings in the inner tangential wall. Thickenings, in the shape of a continuous plate, in the outer tangential wall is restricted to three neotropical genera, Alibertia, Amaioua and Borojoa . Presence of distinct knobs is common in palaeotropical genera, whereas in neotropical genera this feature is only present in Casasia and Kotchubaea . It is concluded that data on exotesta morphology alone does not support any of the previously proposed informal groups, but may still be an important character to deduce phylogenetic relationships, primarily on a level just above the genus.