Plant Systematics BSC 5993 (Week 7 = February 23, 2001)

Use of Anatomical and Morphological Characters

by Jack B. Fisher (jfisher@fairchildgarden.org)

Concept of biological homology

Analogous structures = similar in function but different in evolutionary origin, e.g. spines (derived from modified epidermal tissue, leaf, or root), inflorescence of Asteraceae and a flower.

Homoplasy = Convergence of form: seen in tendrils (derived from leaf, shoot, root,) or succulent stems (in Cactaceae, Euphorbiaceae); parallelism or independent origin of similar feature (different phylogeny of petaloid staminodes in Zingiberaceae).

Homologous structures = similar in evolutionary origin but not necessarily with similar function or structure (form).

Criteria of homology (given by A. Remane see Kaplan, 1984)

1. Equivalent positions within general ground plan.
2. Equivalent special quality
3. Connection of differing structures by intermediate forms

Typology = Grouping under or relating specific example to a generalized plan of organization (Bauplan, ground plan). biological homology

Structural characters

Vegetative

• Vegetative organs (leaves, bracts, cotyledons) concept of serial homology (das Blatt, J.W. von Goethe in 1790)

· Habit (herbaceous vs. woody)

• Organography (specializations)
• Microscopic structures (vascular tissues, wood [xylem] and bark [phloem + periderm] anatomy, stomates, meristem organization)

Reproductive

· Flowers/fruits/seeds/ovules/pollen (typology mainly used interpreting variants in flower parts)

Specific Examples

1. Variations in flower parts and numbers interpreted by typology and ontogenetic evidence
2. Variations in development (apical meristems), e.g. dichotomy or dichotomous branching in some algae, ferns and fern allies, and monocotyledons.
3. Endosperm development in basal angiosperms.
4. Vascular tissues: phloem cytology, wood (secondary xylem) characters

References

Baas, P., E. Wheeler & M. Chase. 2000. Dicotyledonous wood anatomy and the APG system of angiosperm classification. Bot. J. Linn. Soc. 134: 3-17.

Endress, P.K. 1994. Diversity and evolutionary biology of tropical flowers. Cambridge University Press, Cambridge.

Fisher, J.B. & K.J. Maidman. 1999. Branching and architecture in palms: value for systematics. In A. Henderson & F. Borchsenius (eds.) Evolution and Variation, and classification of palms. Mem. N.Y. Bot. Gard. 83: 35-46.

Floyd, S.K. & W.E. Friedman. 2000. Evolution of endosperm developmental patterns among basal flowering plants. Int. J. Plant Sci. 161 (6 Suppl.): S57-S81.

Gifford, E.M. & A.S. Foster. 1989. Morphology and evolution of plants. Third Ed. Freeman & Co., New York.

Herendeen, P.S. & R.B. Miller. 2000. Utility of wood anatomical characters in cladistic analyses. Int. Assoc. Wood Anat. J. 21: 247-276.

**Judd, W.S et al. 1999. Plant systematics: a phylogenetic approach. Sinauer Associates, Sunderland, MA. Chapter 4.

Kaplan, D.R. 1984. The concept of homology and its central role in the elucidation of plant systematic relationships. In Duncan, T. & T.F. Stuessy (eds.) Cladistics: Perspectives on the reconstruction of evolutionary relationships. Columbia University Press, New York. Pp. 51-70.

Scotland, R. & R.T. Pennington (eds.) 2000. Homology and systematics. Taylor & Francis, London.

Tucker, S.C. 1997. Floral evolution, development, and convergence: the hierarchial-significance hypothesis. Int. J. Plant Sci. 158 (6 Suppl.): S143-S161.