Phyllotaxis in Asphodelaceae subfam. Alooideae: A Tool in Taxon Delimitation
2022
Molteno, Steven
The genera and species of Asphodelaceae subfam. Alooideae, a predominantly leaf-succulent group, display significant diversity in their phyllotaxis. However, recording, describing, and studying this character for the ca. 1000 species included in the subfamily have not received comprehensive attention to date. An introduction to phyllotaxis is presented, along with a non-destructive method for describing and studying this character in the group. It is concluded that the divergence angle apparent in mature rosettes or stems is most suitable for describing the diverse alooid phyllotaxis systems. This is additionally a less invasive tool than other procedures such as those that record the plastochron ratio or leaf arc. An approach and methodology to studying alooid phyllotaxis is presented, using established phyllotaxis notations with minimal additions. The principal innovation of this approach is that the direction of any curved leaf-ranks is recorded relative to that of the generative spiral, thus rendering their direction of curvature regular and predictable. Furthermore, it is concluded that systematically recording phyllotaxis in the Asphodelaceae subfam. Alooideae has significant diagnostic utility, at both genus and species ranks. In future, including the phyllotaxis formula, in the suggested notation, as part of the descriptions of all alooid taxa will be taxonomically useful. The method is illustrated in the genera Aristaloe, Astroloba, Gasteria, Gonialoe, Haworthiopsis and Tulista.
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