Developmental patterns in anatomy are shared among separate evolutionary origins of stem succulent and storage root-bearing growth habits in Adenia (Passifloraceae)

The architecture of flowering plants is astonishingly diverse. To understand evolutionary patterns and processes that account for this diversity, I investigated developmental anatomy of storage roots and stems of 58 species in the genus Adenia (Passifloraceae) using an explicit phylogenetic context....

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Bibliographic Details
Published in:American journal of botany 2009-11, Vol.96 (11), p.1941-1956
Main Author: Hearn, David J
Format: Article
Language:English
Subjects:
Adenia
Anatomy
Anatomy and Morphology
Bayesian comparative analysis
Biodiversity
Botany
cambial variants
Developmental biology
Evolution
Flowers & plants
Genetics
growth habit
hypermorphosis
innervation hypothesis
parallelism
Parenchyma
Passifloraceae
Phloem
Plant roots
Plants
stem succulence
storage roots
Succulent plants
switch‐like evolution
Woody vines
Xylem
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Summary:The architecture of flowering plants is astonishingly diverse. To understand evolutionary patterns and processes that account for this diversity, I investigated developmental anatomy of storage roots and stems of 58 species in the genus Adenia (Passifloraceae) using an explicit phylogenetic context. Because expanded storage roots and stem succulence evolved multiple times in Adenia, patterns of transition between succulent and nonsucculent forms were analyzed using a comparative test that accommodates phylogenetic uncertainty. I tested the innervation hypothesis, wherein I expected the evolution of vascular strands to be correlated with evolutionary increases in water storage tissue if evolution of vascular strands facilitates transport through water and starch storage structures. Not only is evolution of vascular strands in stems statistically coupled with evolutionary increases in parenchyma storage tissue, most lineages that evolved expanded storage roots also evolved vascular strands in these roots in parallel to succulent stems. I proposed that vascular strands and closely associated storage parenchyma found in both roots and shoots of Adenia comprise a homologous unit. A switch-like evolutionary mechanism that alters the spatial expression of this unit between roots and shoots can account, in large part, for transitions between markedly different habits such as storage-rooted herbs and succulent-stemmed shrubs.
ISSN:0002-9122
1537-2197
DOI:10.3732/ajb.0800203