Microsporogenesis and pollen sulcus type in Asparagales (Lilianae)

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Abstract
Cladistic analysis of molecular data (plastid rbcL sequences) supports the interpretation of simultaneous microsporogenesis as an apomorphy for Asparagales (Lilianae), with a reversal in the most derived 'higher' asparagoid clade, which is entirely successive. 'Lower' asparagoids are mainly simultaneous, with occasional reversals to the successive state, such as in Xanthorrhoea, Hypoxidaceae, and a few Orchidaceae and Iridaceae (including Geosiris). Trichotomosulcate pollen, a characteristic feature of one of the lower asparagoid clades, is associated with simultaneous microsporogenesis. Some lower asparagoids, such as Doryanthes and a few Iridaceae, are recorded as having both successive and simultaneous microsporogenesis. Irregular tetrads occur frequently in Asphodelaceae and sometimes in higher asparagoids, although not in the group with trichotomosulcate pollen. We relate the distributions of these characters to the positions of the same taxa in the rbcL tree, expanded to include more taxa sampled for pollen characters. The pollen data are highly congruent with the rbcL tree, although when viewed from the perspective of all previous classifications, trichotomosulcate pollen would be interpreted to have evolved several times. We interpret distribution of both simultaneous microsporogenesis and trichotomosulcate pollen with the DNA tree to be an indication of the reliability of both for taxonomic revision of family limits. Key words: tetrads, trichotomosulcate pollen, Phormiaceae.