Character Description in Phylogenetic Analysis: Insights from Agnes Arber's Concept of the Plant

Abstract

Throughout her work Agnes Arber argues for an inclusive, synthetic concept of the vascular plant as `consisting of a unification of every phase of its existence'. Her view of the leaf as a partial-shoot reflects this unification by relating the part (leaf) to the whole (shoot). According to Arber's view of the plant, the part can be fully understood only in the context of the whole. Morphological character description as it is currently practiced in systematics isin sharp contrast with this holistic view of plant structure. Systematic characters are removed from their context when they are described. This problem is greatest when characters are expressed verbally. Verbal descriptions convey little of the content of the character. A shift from verbal to visual charactersallows systematists to capture more information, including some of the context in which the character occurs. By using a photograph, the fringe on a labellum of Alpinia spp. (Zingiberaceae) can be viewed in the context of the labellum in a way that the word `fringe' cannot convey. The use of pictorial charactersalso allows reliable data storage and retrieval from databases, much as DNA sequences are currently being stored and retrieved.

Complex Data Produce Better Characters

“…However, in spite of the complexity of trait combinations in the hybrids, the individual ratings never differed by more than 1 point on any of the 250 plants that were scored. This level of agreement occurred in spite of the fact that different observers had contrasting research interests related to different aspects of plant morphology (see Stevens, 2001, andKirchoff, 2001 for a discussion of how this might have affected the ratings).…”

“…The labeling process begins with the reduction of the initial variability in attributes to produce a trait of a taxon through the use of a label. For instance, a complex labellum may be labeled "obdeltoid," thereby reducing all aspects of its shape to something that is inverted and broadly triangular (Kirchoff, 2001). Once developed, this label is then applied to the scoring of new attributes.…”

Agnes Arber: form in the mind and the eye

“…What is lacking is Arber's sixth step: taking the long view and examining the philosophical underpinnings of this work, finding ways to see the unity and meaning behind this information. Kirchoff (2001b) also argues that, while present-day morphologists do not usually take Arber's holistic approach, there is a greater shift to the use of visual information, which is very much in keeping with her work. This shift "allows systematists to capture more information, including some of the context in which the character occurs" (p. 1203), thus indirectly leading to a more holistic viewpoint.…”

Reproductive morphology of Sargentodoxa cuneata (Lardizabalaceae) and its systematic implications

“…In their treatment of the mature female flowers, they describe the sterile, rudimentary stamens as ''petaloid staminodes'' (Zhang and Ren 2008). While these stamens do resemble the petals of Sargentodoxa, the use of the term ''petaloid'' suggests that they resemble more or less normal petals of a more typical flower and is probably best avoided for these staminodes (Kirchoff 2001;Kirchoff et al 2009). …”