| Abstract: | The three species of Uebelmannia (Cactaceae: Cactoideae; endemic to Minas Cerais, Brazil) are noteworthy for their tough, bumpy stem surface and the presence of conspicuous mucilage cavities restricted to the outer part of the stems. The anatomy of the mature structures and their ontogeny was investigated from microtome sections. The uncommon surface relief is caused by groups of unequally elongated hypodermis cells. The mucilage cavities consist of solitary and considerably enlarged mucilage cells (U.buiningii and U. pectinifera). In U.gummifera groups of mucilage cells disintegrate and form large cavities which are finally united into longitudinal ducts. A comparison of these stem features with species of the superficially similar genera Islaya and Wigginsia (representing tribe Notocacteae), does not indicate a close phylogenetic relationship between Uebelmannia and members of tribe Notocacteae. Finally, some short comments touch on the adaptational aspect of the characteristic stem features of Uebelmannia. |
