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(American Journal of Botany. 2005;92:1765-1773.)
© 2005 Botanical Society of America, Inc.

Anatomy and Morphology

Development of woody branch attachments in Schefflera (Araliaceae or Apiaceae)1

P. Barry Tomlinson2,6, Jack B. Fisher3, Francis Hallé4 and Randol Villalobos5

2Harvard Forest, Harvard University, Petersham, Massachusetts 01366 USA and The Kampong of the National Tropical Botanical Gardens, 4013 Douglas Road, Coconut Grove, Florida 33133 USA; 3Fairchild Tropical Botanic Garden, 11935 Old Cutler Road, Coral Gables, Florida 33156 USA and Department of Biological Sciences, Florida International University, Miami, Florida 33199 USA; 4109 Ave. de Lodève, Montpellier, 34070 France; 5Department of Biology, University of Miami, Coral Gables, Florida 33144 USA

ABSTRACT

Attachment of branches in Schefflera is unusual in that it involves fingerlike woody extensions that originate in the cortex and pass gradually into the woody cylinder of the parent shoot. We tested the hypothesis that these structures could be roots since Schefflera is a hemi-epiphyte with aerial roots. These branch traces originate by secondary development in the many leaf traces (LTs) of the multilacunar node together with associated accessory traces. In the primary condition, the LTs may be described as cortical bundles. Leaves are long persistent and can maintain a primary stem connection across a broad cylinder of secondary xylem. Under the stimulus of branch development, the LTs form a template for secondary vascular development. Because the LT system is broad, with many traces, the branch attachment is also broad. The fingerlike extensions are attached to the surface of the woody cylinder of the parent stem but are progressively obscured as a continuous cambium is formed. Bark tissues are included within the branch axil because of the extended cortical origin of the initial attachment. The results are discussed in the context of branch-trunk unions in tropical plants, an important component of canopy development.

Key Words: Araliaceae • branch insertion • leaf gap • leaf trace • nodal anatomy • Schefflera • secondary xylem






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