Do. Cornejo et Bb. Simpson, ANALYSIS OF FORM AND FUNCTION IN NORTH-AMERICAN COLUMNAR CACTI (TRIBEPACHYCEREEAE), American journal of botany, 84(11), 1997, pp. 1482-1501
Simple and multivariate linear models were used to demonstrate the inf
luence of mechanical design and climate on stem morphology and branchi
ng architecture in 15 species of North American columnar cacti. The ef
fect of phyletic inertia was tested by the method of independent contr
asts. Stem with was found to increase significantly slower with increa
sed height within taxa (cross-sectional stem area proportional to [pla
nt height](0,603)), than across taxon (cross-sectional stem area propo
rtional to [plant height](1,451)). Juveniles are shown to be mechanica
lly overbuilt and subsequently grow into more slender adult forms dete
rmined in part by structural limitations and the optimization of other
stem functions. We make a structural analogy of relatively rigid colu
mnar cacti to concrete columns and compare plants and models with simi
lar growth forms lacking woody skeletons (barrel cacti). Taxa with woo
dy support achieved a surface-to-volume ratio six times greater than t
axa without woody support. Across taxon, coder winter temperatures wer
e associated with larger stem girths, and greater annual precipitation
was associated with Less frequent branching. The relationship between
total plant surface and volume approaches isometry within taxa, but a
cross taxon average individuals are scaled replicates. We hypothesize
that architecture and average plant height are adjusted, in an evoluti
onary sense, to maintain geometric similitude between surface and volu
me along a climatic gradient.