Subpseudocolpi in polyads of Acacia, subgenus Aculeiferum

Abstract

A revision of the pollen morphology of American species of Acacia, subgenus Aculeiferum, section Monacanthea allowed to characterize, in some species, a new structure: ''subpseudocolpi'' on the distal areas of the grains. Equivalent structures have been found in polyads of some species of Stryphnodendron. The structure is not easily observed under the light microscope, since the reduction of the exine is present only in the infratectal granular layer. It produces an infratectal discontinuity area parallel to the edge of the distal face of the grains, thus allowing folding inwards and outwards of the whole distal polar area delimitated by the ''discontinuity''. As, this feature does not correspond with the concept of pseudocolpus present in subgenus Phyllodinae, which have a reduction of the tectum, a new term: ''subpseudocolpus'', is proposed. The presence of subpseudocolpi (=incipient pseudocolpi) in some species of Stryphnodendron reinforced the pleiophyly hypothesis on the origin of the Acacia considering it to be derived from the Piptadenia group in tropical America.