Structure of pollen apertures in the Detarieae sensu stricto (Leguminosae: Caesalpinioideae), with particular reference to underlying structures (Zwischenkörper).

This study presents the pollen aperture morphology of 148 out of approx. 200 species in 16 genera of the Detarieae s.s. and 13 related genera, investigated with light microscopy, scanning electron microscopy and transmission electron microscopy, using various staining techniques. Features of detarioid legume pollen apertures are described, illustrated and discussed in relation to function and phylogeny. Protruding apertures in the mature pollen grains of taxa in the Detarieae s.s are associated with underlying structures composed of pectic substances called 'Zwischenkörper'. This is the first report of Zwischenkörper in legume pollen. A review of previous literature on Zwischenkörper, evidence of how they differ from onci, and a discussion of developmental origins, terminology and function, is given. Zwischenkörper occur in pollen of Daniellia, Eurypetalum, Eperua, Augouardia, Stemonocoleus, Baikiaea, Copaifera, Pseudosindora, Detarium, Sindora, Sindoropsis, Tessmannia, Gilletiodendron, Hylodendron, Hymenaea, Peltogyne and Guibourtia of the Detarieae s.s. clade of recent molecular analyses. Exinous projections and/or bridges are present over the centre of apertures in the pollen of Sindora, Copaifera, Detarium, Pseudosindora, Hylodendron and Sindoropsis, and may cover the Zwischenkörper of live pollen. Zwischenkörper also occur in the closely related genus Barnebydendron, the sister genus to the Detarieae s.l. clade Goniorrhachis, and also Cercis of the sister clade to the Detarieae s.l. plus Goniorrhachis. A modified form of Zwischenkörper occurs in the pollen of Schotia. Zwischenkörper were not detected in the genera Colophospermum, Prioria, Gossweilerodendron, Oxystigma, Kingiodendron and Hardwickia of the Prioria clade, or in Endertia, Lysidice and Saraca of the Amherstieae clade. None of these taxa have protruding apertures.