comparison between the record height-to-stem diameter allometries of Pachycaulis and Leptocaulis species

• Published in: Annals of botany 2006, Vol.97 (1), p.79-83
• Main Authors: Niklas, K.J, Cobb, E.D, Marler, T
• Format: Article
• Language: English
• Subjects: Adaptation, Physiological; Allometry; Apiaceae; Arecaceae; Biological taxonomies; Cactaceae; cacti; Cactus; Confidence interval; Conifers; critical buckling heights; Cycadophyta; cycads; diameter; Evolution; Growth habit; height; Original; Pachycaulis; palms; plant architecture; Plant biomechanics; plant growth; plant morphology; Plant Stems - anatomy & histology; Plant Stems - growth & development; Plant Stems - physiology; Plants; Species; Spermolepis; stem allometry; stems; Trees; Trees - anatomy & histology; Trees - growth & development; Trees - physiology
• ISSN: 0305-7364; 1095-8290
• DOI: 10.1093/aob/mcj002

BACKGROUND AND AIMS: The interspecific allometry of maximum plant height (H[subscript max]) with respect to maximum basal stem diameter (D[subscript max]) 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 H[subscript max] with respect to D[subscript max]. 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 logH[subscript max] vs. logD[subscript max] reduced major axis regression curves (and their respective 95 % confidence intervals) were used to compare the four species groups. The stem slenderness ratio (H[subscript max]/D[subscript max] = R[subscript max]) 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.