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Systematic studies of the Saxifragaceae s.l., chiefly from the southern hemisphere.

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posted on 2015-11-19, 08:59 authored by Khalil Ibrahim Abbass. Al-Shammary
Engler's Saxifragaceae has long been recognised as a heterogeneous family. In particular, the southern hemisphere subfamily Escallonioideae is poorly known and its composition and relationships have not been established. The aim of this study was primarily to provide sufficient data in order to solve these problems, and secondly to examine the monophyletic nature (or otherwise) of the family. The present study therefore investigated the following genera from Engler's Escallonioideae: Cuttsia, Abrophyllum, Carpodetus, Corokla, Argophyllum, Forgesia, Choristylis, Quintinia, Escallonia, Valdivia, Tribeles, Polysoma and Anopterus, as well as southern hemisphere genera from other subfamilies (Vahlia, Montinia, Grevea, Eremosyne, Bauera, Tetracarpaea, Brexia, Ixerba, Roussea, Francoa, Tetilla, Lepuropetalon) and a few possibly related northern hemisphere genera (Ribes, I tea, Parnassia). The evidence gathered came from studies of leaf venation, leaf epidermal morphology and anatomy (including studies of trichomes), nodal anatomy, iridoid chemistry, SEM and TEM observations of pollen morphology and anatomy, and seed morphology and anatomy. This was amalgamated with other published data, e.g. on floral morphology, and cladistic analyses conducted using both Wagner and Camin-Sokal parsimony methods. The first set of analyses dealt with the genera listed above. A second set included other subfamilies and tribes from the Saxifragaceae, as well as other families, e.g. Celastraceae, Cornaceae, Cunoniaceae, Droseraceae, Pittosporaceae, and Ericaceae. The analyses indicated that the Escallonioideae comprise Cuttsia, Abrophyllum, Carpodetus, Corokia, Argophyllum, Forgesia, Quintinia, Escallonia and Valdivia; the Montinioideae contain Montinia and Grevea; Polyosma, Anopterus, Vahlia and Eremosyne are related to these two groups; and the whole would be best placed in Dahlgren's Cornales, along with the Hydrangeoideae, chiefly on account of the presence of iridoids. Family status is recommended for the Escallonioideae, Montinioideae, Hydrangeoideae, Vahlia and Eremosyne; further work is needed to establish the precise positions of Polyosma and Anopterus. Engler's concept of tribe Francoeae (Francoa and Tetilla) was supported; its relationships are not directly with the Saxifrageae but may lie with Lepuropetalon, Parnassia and Tribeles, not in the Cornales but possibly in the Saxifragales. Brexia, Ixerba and Roussea (Engler's Brexioideae) appeared to be monophyletic in the first analysis but a second one demonstrated that this heterogeneous group should be broken up; the relationships of the genera are still uncertain but may lie with the Celastraceae, along with Choristylis, Pottingeria, Ptersostemon, and Phyllonoma. Bauera and Tetracarpaea were confirmed as not belonging to the Escallonioideae; the former is related to and could be included in the Cunoniaceae, whilst the latter is best treated as a taxonomically isolated independent family. Ribes is closely allied to the tribe Saxifrageae (excluding Vahlia), and does not belong in the Escallonioideae. Engler's Saxifragaceae is therefore probably not monophyletic and should be broken up along the lines indicated above.


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University of Leicester

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  • Doctoral

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  • PhD



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