Bot. Rev. DOI 10.1007/s12229-010-9057-5 Paedomorphosis, Secondary Woodiness, and Insular Woodiness in Plants Max W. Dulin1 & Bruce K. Kirchoff1,2 1 Department of Biology, University of North Carolina at Greensboro, 321 McIver St., P. O. Box 26170, Greensboro, NC 27402-6170, USA 2 Author for Correspondence; e-mail: [email protected] # The New York Botanical Garden 2010 TABLE OF CONTENTS I. Abstract ................................................................................................................ II. Introduction ......................................................................................................... III. Historical Review............................................................................................... A. Paedomorphosis, Insular Woodiness, and Secondary Woodiness.............. B. Paedomorphosis........................................................................................... 1. Genesis of the Theory of Paedomorphosis......................................... 2. Bailey’s Refugium Theory and Major Trends in Xylem Evolution... 3. Paedomorphic Characters of the Secondary Xylem........................... C. Insular Woodiness....................................................................................... 1. Examples of Insular Woodiness......................................................... 2. Relictual and Secondary Insular Woodiness...................................... 3. Hypotheses to Expain the Evolution of Insular Woodiness............... D. Secondary Woodiness ................................................................................. IV. Stem Structure and Wood Anatomy in Xanthorhiza simplicissima, Coreopsis gigantea, and Mahonia bealei.......................................................................... A. Overview..................................................................................................... B. Organography and Anatomy ....................................................................... 1. Xanthorhiza simplicissima................................................................. 2. Coreopsis gigantea............................................................................ 3. Mahonia bealei.................................................................................. C. Materials and Methods................................................................................ D. Results ........................................................................................................ 1. Stem Anatomy and Xylem Characteristics of Xanthorhiza simplicissima ........................................................................................ a. Overview.............................................................................. b. Vessels................................................................................. c. Rays ..................................................................................... d. Fibers................................................................................... e. Secondary Woodiness.......................................................... M.W. Dulin, B.K. Kirchoff 2. Stem Anatomy and Xylem Characteristics of Coreopsis gigantea.… a. Overview.............................................................................. b. Parenchyma in Younger Stems............................................ c. Vessels in Younger Stems.................................................... d. Parenchyma in Older Stems................................................. e. Vessels in Older Stems ........................................................ f. Rays in Older Stems............................................................. g. Fibers in Older Stems .......................................................... h. Secondary Woodiness ......................................................... 3. Stem Anatomy and Xylem Characteristics of Mahonia bealei.......... a. Overview.............................................................................. b. Vessels................................................................................. c. Rays ..................................................................................... d. Fibers ................................................................................... e. Secondary Woodiness.......................................................... 4. Paedomorphosis in Primitively Woody Taxa..................................... V. Discussion .......................................................................................................... A. Xanthorhiza simplicissima .......................................................................... 1. Vessels................................................................................................ 2. Rays.................................................................................................... 3. Fibers.................................................................................................. 4. Paedomorphosis ................................................................................. 5. Secondary Woodiness ........................................................................ 6. Environmental Factors and Anatomy................................................. B. Coreopsis gigantea ..................................................................................... 1. Vessels ............................................................................................... 2. Rays.................................................................................................... 3. Fibers .................................................................................................. 4. Paedomorphosis in the Secondary Xylem.......................................... 5. Secondary Woodiness ........................................................................ 6. Environmental Factors and Anatomy................................................. C. Mahonia bealei ........................................................................................... 1. Vessels ............................................................................................... 2. Rays.................................................................................................... 3. Fibers .................................................................................................. 4. Paedomorphosis ................................................................................. 5. Secondary Woodiness ........................................................................ 6. Environmental Factors and Anatomy................................................. D. Paedomorphosis in the Secondary Xylem .................................................. 1. The Baileyan Trends........................................................................... 2. Mabberly’s Criticism of Paedomorphosis.......................................... E. Secondary and Insular Woodiness .............................................................. F. Paedomorphosis with Primary Woodiness .................................................. G. Paedomorphic Rays and Raylessness ......................................................... H. The Concept of Woodiness in Relationship to Plant Growth Forms.......... VI. Conclusions........................................................................................................ VII. Acknowledgements........................................................................................... VIII. Literature Cited ............................................................................................... Paedomorphosis, Secondary Woodiness, and Insular Woodiness in Plants Keywords Wood · Secondary Xylem · Evolution · Paedomorphosis · Xanthorhiza · Mahonia · Coreopsis Herbaceous · Woody I. Abstract The related concepts of paedomorphosis in the secondary xylem, insular woodiness, and secondary woodiness are reviewed and evaluated in order to clearly distinguish the phenomenon involved, and provide a firm foundation for future research in this area. The theory of paedomorphosis refers to the occurrence of certain juvenile xylem characteristics, such as scalariform perforation plates and lateral wall pitting, in the secondary xylem of shrubby, suffrutescent, pachycau- lous, and lianoid growth forms. Paedomorphic characteristics are often found in insular woody species, a fact that has caused paedomorphosis to be associated with secondary woodiness. The anatomy of the secondary xylem in Xanthorhiza simplicissima (Ranunculaceae), Coreopsis gigantea (Asteraceae), and Mahonia bealei (Berberidaceae) is described in order to provide specific data for discussion. These species serve as test cases for the presence of paedomorphosis, and the evolution of secondary woodiness. The secondary xylem of all three species was found to have a degree of paedomorphosis, with Coreopsis having the greatest number of paedomorphic characteristics, Xanthorhiza having an intermediate number, and Mahonia possessing only a single characteristic. Plotting the occurrence of the character states woody and nonwoody on phylogenetic trees containing these taxa shows that Coreopsis is secondarily woody, while the ancestry of the other two species cannot be unambiguously established. These results must, however, be considered preliminary as the occurrence of secondary growth in many “herbaceous” plants often goes unreported. Although paedomorphosis is often associated with secondary woodiness,