Pollen morphology of Lactoridaceae — a re-examination

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Abstract
Lactoris fernandeziana Philippi, the sole member of the primitive dicotyledonous family Lactoridaceae, occurs on Masatierra Island of the Juan Fernandez archipelago. A study of its pollen, utilizing preserved flowers, disproved conclusions, based on pollen from herbarium material, that the permanent tetrahedral pollen tetrads have large sacci (Zavada & Taylor 1986, Carlquist 1964) and are anasulcate. A small, poorly defined, aperture is formed at the distal pole of each grain, but before pollen is released, premature bulging of the pollen tube through this aperture, gives the impression of a much larger one. Exine sculpturing is scabrate to microrugulate and in equatorial view the exposed surfaces of each grain contain many folds. The tectum has minute perforations and an infratectal region of granules which are sometimes fused to form incipient columellae. Tetrads are of the calymmate type in which the ektexine is continuous across the external walls of neighbouring pollen grains, but only tenuous links occur between the internal walls. There is a poorly developed foot layer, which is absent, or has a granular appearance, in some regions. Endexine is lacking and the intine has an outer region containing tubular material. Lactoris may have the same pollinator(s) as the Juan Fernandez endemic Drimys confertifolia (family Winteraceae) as a number of permanent tetrads of this species were found on stigmas of Lactoris. The pollen morphology of Lactoridaceae underscores the isolated position of this family within Magnoliidae.