AOBPreview originally published online on October 27, 2005
Annals of Botany 2006 97(1):79-83; doi:10.1093/aob/mcj002
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A Comparison between the Record Height-to-Stem Diameter Allometries of Pachycaulis and Leptocaulis Species
1 Department of Plant Biology, Cornell University, Ithaca, NY 14853, USA and 2 College of Natural and Applied Sciences, University of Guam, Mangilao, Guam 96923, USA
* For correspondence. E-mail kjn2{at}cornell.edu
Received: 29 June 2005 Returned for revision: 31 August 2005 Accepted: 12 September 2005 Published electronically: 27 October 2005
• Background and Aims The interspecific allometry of maximum plant height (Hmax) with respect to maximum basal stem diameter (Dmax) has been studied for leptocaulis dicot and conifer tree species. In contrast, virtually nothing is known about the interspecific allometry of pachycaulis species. Here, the interspecific allometries for palms, cacti and cycads are reported and compared with those of leptocaulis dicot and conifer tree species to determine whether pachycauly limits Hmax with respect to Dmax.
• Methods Data for each of a total of 1461 pachycaulis and leptocaulis species were gathered from the primary literature. The scaling exponent and the allometric constant of logHmax vs. logDmax reduced major axis regression curves (and their respective 95 % confidence intervals) were used to compare the four species groups. The stem slenderness ratio (Hmax/Dmax = Rmax) for each species was also computed to compare interspecific trends in trunk shape.
• Key Results and Conclusions Each of the four species groups is allometrically unique, i.e. no single ‘canonical’ maximum plant height to stem diameter allometry exists across all four species groups. Although pachycaulis does not intrinsically limit height, height is nevertheless limited by the size range of basal stem diameter occupied by each species group. Pachycaulis species achieve heights comparable to some leptocaulis species by virtue of very high slenderness ratios attended by an absence or paucity of stem branching. The diversity observed for pachycaulis stem allometries is likely the result of the independent evolutionary origins of this growth habit and the different anatomical strategies used to stiffen stems.
Key words: Plant biomechanics, cacti, critical buckling heights, cycads, palms, stem allometry
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