Journal Article

The multiple fuzzy origins of woodiness within Balsaminaceae using an integrated approach. Where do we draw the line?

Frederic Lens, Sharon Eeckhout, Rosa Zwartjes, Erik Smets and Steven B. Janssens

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 109, issue 4, pages 783-799
Published in print March 2012 | ISSN: 0305-7364
Published online December 2011 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcr310
The multiple fuzzy origins of woodiness within Balsaminaceae using an integrated approach. Where do we draw the line?

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Background and Aims

The family Balsaminaceae is essentially herbaceous, except for some woodier species that can be described as ‘woody’ herbs or small shrubs. The family is nested within the so-called balsaminoid clade of Ericales, including the exclusively woody families Tetrameristaceae and Marcgraviaceae, which is sister to the remaining families of the predominantly woody order. A molecular phylogeny of Balsaminaceae is compared with wood anatomical observations to find out whether the woodier species are derived from herbaceous taxa (i.e. secondary woodiness), or whether woodiness in the family represents the ancestral state for the order (i.e. primary woodiness).

Methods

Wood anatomical observations of 68 Impatiens species and Hydrocera triflora, of which 47 are included in a multigene phylogeny, are carried out using light and scanning electron microscopy and compared with the molecular phylogenetic insights.

Key Results

There is much continuous variation in wood development between the Impatiens species studied, making the distinction between herbaceousness and woodiness difficult. However, the most woody species, unambiguously considered as truly woody shrubs, all display paedomorphic wood features pointing to secondary woodiness. This hypothesis is further supported by the molecular phylogeny, demonstrating that these most woody species are derived from herbaceous (or less woody) species in at least five independent clades. Wood formation in H. triflora is mostly confined to the ribs of the stems and shows paedomorphic wood features as well, suggesting that the common ancestor of Balsaminaceae was probably herbaceous.

Conclusions

The terms ‘herbaceousness’ and ‘woodiness’ are notoriously difficult to use in Balsaminaceae. However, anatomical observations and molecular sequence data show that the woodier species are derived from less woody or clearly herbaceous species, demonstrating that secondary woodiness has evolved in parallel.

Keywords: Balsaminaceae; herbaceousness; Hydrocera; Impatiens; insular woodiness; light microscopy; primary woodiness; secondary woodiness; wood anatomy

Journal Article.  9006 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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