Pollen Ultrastructure of the Tecophilaeaceae

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Abstract
The classification of the monocot family Tecophilaeceae has been variable. Pollen ultrastructural studies using SEM and TEM were made in an attempt to resolve taxonomic problems. Six genera of the Tecophilaeaceae: Conanthera, Cyanella, Odontostomum, Tecophilaea, Walleria, and Zephyra, are palynologically similar in having monosulcate, heteropolar, generally foveolate (rugulose in one genus) pollen grains with a tectate-columellate exine architecture and an operculate aperture. The operculum, which is hypothesized to be a shared derived character for these six genera, consists of a band of tectate-columellate exine positioned median and parallel to the aperture. An electron-dense, apparently endexinous layer occurs inner to the ektexine both in the operculum and along the aperture periphery. Walleria differs among these taxa in that the operculum consists of a band of granular ektexine atop the endexinous basal layer. The genus Cyanastrum, sometimes classified in the Tecophilaeaceae, has monosulcate, heteropolar, regulose, tectate-columellate pollen grains which, however, lack an operculum. Thus, the present study tends to support the classification of Cyanastrum in a separate, monotypic family, the Cyanastraceae, Eriospermum, a genus sometimes placed in or suggested to have close affinities with the Tecophilaeaceae (particuarly with Walleria), has pollen which is monosulcate, heteropolar, foveolate to reticulate with a tectate-columellate exine. However, grains of Eriospermum lack an operculum and an endexinous basal layer, providing no supporting evidence for the close relationship of Eriospermum to the Tecophilaeaceae. The monosulcate aperture type and tectate-columellate exine architecture present in all investigated taxa are hypothesized, by outgroup comparison, to be ancestral features, which are of no value in grouping monophyletic taxa. Previous classifications of the Tecophilaeaceae as a tribe (Conanthereae) of the family Haemodoraceae are refuted based on comparative studies.