Journal Article

Root Character Evolution and Systematics in Cranichidinae, Prescottiinae and Spiranthinae (Orchidaceae, Cranichideae)

Coyolxauhqui Figueroa, Gerardo A. Salazar, H. Araceli Zavaleta and E. Mark Engleman

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 101, issue 4, pages 509-520
Published in print March 2008 | ISSN: 0305-7364
Published online February 2008 | e-ISSN: 1095-8290 | DOI: https://dx.doi.org/10.1093/aob/mcm328
Root Character Evolution and Systematics in Cranichidinae, Prescottiinae and Spiranthinae (Orchidaceae, Cranichideae)

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  • Ecology and Conservation
  • Evolutionary Biology
  • Plant Sciences and Forestry

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Background and Aims

Previous studies have suggested that velamen characteristics are useful as taxonomic markers in Orchidaceae. Members of tribe Cranichideae have been assigned to two velamen types constructed based on combinations of characters such as the presence of secondary cell-wall thickenings and pores. However, such characters have not been analysed on an individual basis in explicit cladistic analyses.

Methods

The micromorphology of roots of 26 species of Cranichideae was examined through scanning electron microscopy and light microscopy, scoring the variation and distribution of four characters: number of velamen cell layers, velamen cell-wall thickenings, presence and type of tilosomes, and supraendodermal spaces. The last three characters were analysed cladistically in combination with DNA sequence data of plastid trnK/matK and nuclear ribosomal internal transcribed spacer (ITS) regions and optimized on the resulting phylogenetic tree.

Key Results

Thickenings of velamen cell walls group Prescottiinae with Spiranthinae, whereas tilosomes, documented here for the first time in Cranichideae, provide an unambiguous synapomorphy for subtribe Spiranthinae. Supraendodermal spaces occur mostly in species dwelling in seasonally dry habitats and appear to have evolved three times.

Conclusions

Three of the four structural characters assessed are phylogenetically informative, marking monophyletic groups recovered in the combined molecular–morphological analysis. This study highlights the need for conducting character-based structural studies to overcome analytical shortcomings of the typological approach.

Keywords: Cranichideae; Cranichidinae; ITS; Orchidaceae; phylogeny; Prescottiinae; trnK/matK; root anatomy; Spiranthinae; tilosomes; velamen

Journal Article.  5957 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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