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Image Title: Stem cross section of Pereskia guamacho
AJB Editor: Judy Jernstedt, University of California - Davis
Intended End User: Teacher, Student
License Details: BSA - Terms for Image Use
Copyright held by: BSA,
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About the Image

Stem cross section of Pereskia guamacho, a member of the eight-species cactus lineage hypothesized to be sister to the remaining 1800 or so species of Cactaceae. Pereskia guamacho is a leafy, dry-forest tree lacking many anatomical traits, such as stem succulence, mucilage cells, delayed periderm, and stem stomata, that are highly conserved in most other cacti. Rather than the evolution of a single “key innovation” early in the cactus lineage, lability of many or all of these traits in the ancestors of Cactaceae, as evidenced by high homoplasy in their outgroups, may have facilitated the morphological leap to a water-storing, photosynthetic stem. This hand section (ca. 200 μM) was stained in cresyl violet acetate and mounted in calcium chloride.

For further detail, see: Ogburn and Edwards—Anatomical variation in Cactaceae and relatives: Trait lability and evolutionary innovation, Volume 96, Issue 2, pages 391–408. Photo credit: R. Matthew Ogburn.

National Science Foundation  Development Supported by the National Science Foundation