Functional Plant Biology Functional Plant Biology Society
Plant function and evolutionary biology

Functional leaf anatomy of plants with crassulacean acid metabolism

Elizabeth A. Nelson A B , Tammy L. Sage A and Rowan F. Sage A
+ Author Affiliations
- Author Affiliations

A Department of Botany, University of Toronto, 25 Willcocks Street, Toronto, ON M5S3B2 Canada.

B Corresponding author. Email:

C This paper originates from a presentation at the IVth International Congress on Crassulacean Acid Metabolism, Tahoe City, California, USA, July–August 2004

Functional Plant Biology 32(5) 409-419
Submitted: 27 October 2004  Accepted: 31 January 2005   Published: 27 May 2005


Crassulacean acid metabolism (CAM) has evolved independently on dozens of occasions and is now found in over 7% of plant species. In this study, the leaf structure of a phylogenetically diverse assemblage of 18 CAM plants was compared with six C3 plants and four C4 plants to assess whether consistent anatomical patterns that may reflect functional constraints are present. CAM plants exhibited increased cell size and increased leaf and mesophyll thickness relative to C3 and C4 species. CAM species also exhibited reduced intercellular air space (IAS) and reduced length of mesophyll surface exposed to IAS per unit area (Lmes / area). The low volume of IAS and low exposure of mesophyll surface to IAS likely increases internal resistance to CO2 in CAM tissues. While this diffusional barrier may limit uptake of CO2 during Phases II and IV, carbon economy could be enhanced through the reduced loss of internal CO2 during all four phases of CAM.

Keywords: Crassulacean acid metabolism; C3; C4; intercellular air space; mesophyll; leaf anatomy.


We thank Thomas Fung, Matthew Lam, Andrew Petrie and Kathy Sault for technical assistance, and Bruce Hall and Riyadh Muhaidat for providing plants from their collections. Special thanks to Dr Nancy Dengler and to the participants of the 2004 CAM congress for insightful discussion. This work was supported by NSERC grant OCP0154273 to RFS and RGPN1555258–04 to TLS.


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