The Ultrastructure of Pollen Found in the Dispersed Sporangia of Arberiella (Glossopteridaceae)

Abstract

Dispersed sporangia of the Arberiella type were isolated from Upper Permian sediments from Hammanskraal, South Africa. The sporangia are morphologically similar to those attached to the scale leaves of Eretmonia, microsporangiate reproductive organs believed to have glossopterid affinity. Pollen isolated from the dispersed sporangia is monosulcate, saccate with 4-7 taeniae on the corpus that are parallel to the long axis of the pollen grain. Pollen wall ultrastructure is alveolar in the saccus regions. In the corpus region the infrastructural layer is composed of irregular shaped rods or partitions. The wall structure of pollen found in the sporangia of Arberiella differs from that found in extant gymnosperms by lacking a complete separation of the sexine and nexine in the saccus region. In a paleolandscape dominated by wind-pollinated gymnosperms, sacci may be a morphological feature of pollen that reduces male-male competition and prevents foreign pollen from occupying the micropylar space that would prevent access to the female by the conspecific pollen. All sacci increase pollen size without requiring an increase in male resource allocation in each pollen grain. This is accomplished in saccate pollen grains with a considerable amount of diversity in shape, size, number, and wall structural characteristics of saccate pollen.