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This strongly supported clade shows a largely unresolved clade with 16 Asian species unresolved or paraphyletic with respect to a mainly North-African clade. The latter was already depicted as a so-called “Azorina clade” by Borsch & al. (2009), who overall pointed out the relationships between the Azorean endemic Azorina, the Cape Verdean endemics C. bravensis and C. jacobaea, and the E. African C. edulis. The current study gives a much more accurate picture of those relationships by defining two well-supported assemblages, sister to Azorina, that diversified during the Pleistocene (1.14 Ma [0.72–5.17], i.e. well after the emergence of the Azores archipelago (starting some 18 Ma ago - Fernandez-Palacios & al. 2011). The neoendemic genus Azorina has quickly diverged morphologically from Campanula, and is currently recognized by its shrubby aspect, its typical constricted flowers, and the presence of a flat nectar disk.

The first subclade (C. balfourii, C. bravensis, C. jacobaea, C. keniensis) depicts interesting biogeographical disjunction between a lineage from the Cape Verde Islands of western Africa, including the hexaploid species C. bravensis and C. jacobea (2 n = 54), and an eastern African lineage, with C. balfourii (Socotra) and C. keniensis (2 n = 54; Kenya). Disjunct distributions of plant groups between Macaronesia-NW Africa and E Africa-W Asia have been long recognized under the so-called “Rand Flora” (Sanmartin & al. 2010, Quezel 1978), and include e.g. the famous Canary Island Dracaena draco (Marrero & al. 1998), Phagnalon Montes-Moreno & al. 2010), or Canarina (Campanulaceae; this study). This unexpected E-W relationships has been proposed as one possible explanation for the origin of the Cape Verde lineages by Leyens and Lobin (1994), based on the chromosome number distinctiveness (2 n = 54).

The second subclade (C. afra, C. mollis, C. edulis, C. filicaulis, C. kremeri, C. saxifragoides) contains six species mainly distributed in North Africa. The sister species C. afra and C. kremeri are morphologically very similar and have been treated as subspecies, or even synonyms (Sáez 6 Aldasoro (2003), of C. dichotoma (not included here), with which they share the same chromosome number (2 n = 24) and similar geographical range (western North Africa, C. afra also described in southern Spain) (Valdés & al. 2002). In western Mediterranean Africa, the morphologically and karyologically polymorphic C. filicaulis (Quézel 1953, Contandriopolous 1984), with many potential dysploid and polyploid cytodemes described (2 n = 16, 24, 26, 48, 50, 52, 72), shows genetic affinities with C. saxifragoides (2 n = 14, 16). Finally, the phylogenetic position of the western Mediterranean C. mollis (2 n = 24, 26, 46, 48, 50, 52) and the eastern African C. edulis (2 n = 28, 56, 70) in this subclade remains unclear. Contandriopoulos & al. (1984) interpreted the high polymorphism in chromosome numbers and morphotypes of both C. filicaulis and C. mollis to be the result of recent speciation events and incomplete lineage sorting, an assumption confirmed by the recent origin of the Azorina–C. edulis clade (stem node age = 1,30 Ma [0,98–4,64]).

Overall, the African clade belongs to a larger assemblage including 16 additional species of primarily Asian origin. It is currently unclear whether these lineages are sister or paraphyletic with respect to each other. Most of the Asian species included here are perennial except for two annuals, namely C. dimorphantha (E Africa to Afghanistan and China) and C. pallida (Afghanistan to China). Campanula dimorphantha ( = C. canescens or C. benthamii – Lammers 2003) is a widely distributed species, ranging from N Africa to Taiwan. Interestingly, this species produces both chasmogamous and cleistogamous flowers (the Chinese specimens being mostly cleistogamous), a reproductive strategy that could explain the current large range of this species. The other therophyte (C. pallida) also shows similar mating system and occurs from Afghanistan to Thailand. This species though is sometimes considered a perennial (C. pallida var. tibetica), and cleistogamous forms have also been described under a different species, C. microcarpa C. Y. Wu (Hong & al. 2011), overall adding some taxonomic confusion in the group. Among the remaining perennials, some form morphologically similar groups, including the Afghanistan-Pakistan endemics C. leucantha, C. leucoclada, and C. polyclada, with appendiculate calyces, or C. cashmeriana, C. kermanica and C. khorasanica sometimes treated as subspecies of C. incanescens. On the whole, the taxonomy of the Asian group is far from being resolved, most species being separated by inconspicuous characters. Furthermore, the recent time of divergence of the whole clade would suggest rapid episodes of diversification the polarity of which needs to be investigated.

From: Mansion & al. (2012: 18)


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