Pollen of australian species ofparsonsia(apocynaceae)

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Abstract
Pollen of Australian species of Parsonsia (Apocynaceae) was investigated with LM, SEM and TEM. In external morphology Parsonsia pollen is typical of the subfamily Apocynoideae, being spherical, with a smooth or finely wrinkled surface and is mostly triporate. Differences in pollen size were found between some species, with diameters ranging from 19 um-55 pm. Also differences in the number of apertures per grain, with invariably 3 in one species, 4 in another and, depending on the species 2 and 3; 2, 3 and 4; 3, 4 and 5; 3,4, 5 and 6, in others. Pollen ultrastructure had some features previously unreported in the family. The exine consists of a tectum with an almost smooth surface, containing microperforations, overlying an infratectum which under TEM appears to consist of several uneven layers of tangentially aligned plate-like lamellae. However, use of the ion beam etching technique to strip off the tectum and enable examination of the surface of the infratectum under SEM, as well as examination of the internal surface of the exine of fractured acetolysed grains, showed that the infratectum consisted of an intricate three-dimensional network of anastomosing cylindrical elements of somewhat varying diameter. In some taxa, there is an inner infratectum of inwardly protruding, large oval granules. A foot layer (sole) is absent, but a thin endexine is apparent. Non-apertural intine is 3 layered in some species, a feature not previously reported for the Apocynaceae. In other species the intine has 1 or 2 layers. The ectexine reaches maximum thickness within the annulus surrounding the aperture and becomes thin and fragmented on the surface of the apertural membrane, which appears to contain a thin endexine. Five pollen types were recognized and comparisons made with published reports of pollen ultrastructure of other members of the family.