Pollen morphology of the Gardenieae‐Gardeniinae (Rubiaceae)

Abstract

Pollen grains of 107 species of 61 genera of the Gardeniinae were investigated by scanning electron and light microscopy. The subtribe is europalynous and grains occur either as monads, tetrads or massulae. Grains are porate, colporate or rarely pororate. The majority of the genera has 3‐zonoaperturate pollen grains. However, deviating numbers of apertures occur inByrsophyllum(4–8) andPseudomantalania(4–5). Pantoporate pollen occurs inRandia. The average equatorial size (E) of monads varies between 13 μm inAnomanthodiuto 59 μm inPosoqueria. The tetrads vary from 37 μm inCasasiato 61 μm inCalochoneandEuclinia. The exine is usually reticulate, but also foveolate, rugulate, perforate and psilate exine occurs in the subtribe. The thickness of the exine is only 0.3 μm in tetrad grains ofRandia armataand in the pantoporate monad grains ofR. ruiziana, whereas the thickest exine occurs inPosoqueria(2.8 pm) andEuclinia(2.9 μm). Tectal excrescenses are generally absent. However, three genera with pollen in tetrads, namelyEuclinia, GardeniaandOligoco‐don, show this feature. Contrary to the subtribe most genera are fairly stenopalynous, but in the neotropical generaAlibertiaandRandiaseveral different types of pollen are encountered.