Abstract
- Häffner, E.: On the phylogeny of the subtribe Carduinae (Cardueae, Compositae). – Englera 21: 1-208. 2000.
-
A comparative morphological study of the subtribe Carduinae, tribe Cardueae, Compositae, on genus level was performed in order to reconstruct intergeneric relationships in a cladistic analysis. The Carduinae, which are the largest subtribe of the Cardueae, comprise about 1600 species, many of which are known as thistles and have ecological and economic significance, especially as weeds. The recognition of monophyletic groups within the Carduinae and the relationship between the Carduinae and the closely related subtribe Centaureinae are important aims of the present study.
52 characters, which are phylogenetically informative on the respective taxonomic level, are identified, corresponding to 66 character state transitions. Several new characters are described. Among the most important are the relative length, structure and symmetry of the pappus bristles, the shape and distribution of sclerenchyma elements in the pericarp, the wall reinforcements in the testa epidermis cells, and the shape of the cell walls in the dorsal corolla lobe epidermis. Ontogenetic studies in the achenes have helped to clarify the nature of structures such as the pappus base or the cupula of the Jurinea pappus.
Cladistic analysis of 37 ingroup and three outgroup taxa using the program PAUP yields 48 most parsimonious trees. The results support the monophyly of the Carduinae+Centaureinae (= Cardueae s. str.). Berardia, which has been regarded as a genus of uncertain affinities, is morphologically closest to the hypothetical common ancestor of the Carduinae+ Centaureinae in the cladogram.
Within the ingroup consisting of Carduinae+Centaureinae, several well-supported groups of genera could be identified: the Centaureinae, the Cousinia group, the Jurinea group, the Saussurea group, and the Carduus-Cirsium group. The smaller genera Lamyropsis, Ptilostemon and Cynara form a predominantly Mediterranean complex together with the Carduus-Cirsium group, in which they probably represent early evolutionary lines.
The basal relationships within the ingroup are characterised by a dichotomy which divides the ingroup into two large sister clades. This early split does not correspond to the Carduinae-Centaureinae subdivision. The Carduinae are paraphyletic. The sister group of the Centaureinae contains the large Carduinae complexes around the genera Cousinia, Jurinea and Saussurea, which are mentioned above. The Centaureinae and their sister group are united by morphological synapomorphies such as short outer pappus bristles, a rugose pericarp and undulate cell walls in the dorsal corolla lobe epidermis.
The other large clade produced by the basal dichotomy contains the aforementioned Mediterranean complex as a derived group and the genera Onopordum, Synurus, Alfredia, Olgaea, Xanthopappus, Ancathia and Lamyropappus in a basal paraphyletic grade. The members of this basal grade are characterised by several plesiomorphic features. A plesiomorphic condition for the Carduinae+Centaureinae in general is postulated on the basis of the present results. It manifests itself among others in a straw-coloured fragile pappus, flattened pappus bristles which are scabrous on the dorsal side, the presence of a carpopodium, a strong testa epidermis consisting of radially elongated cells, papillose stamen filaments, an irregular number of main vascular bundles in the pericarp and an alveolate receptacle. Many of these features are present in the genera of the basal grade. Their relictual nature as concluded from their mostly small species numbers and their isolated distribution areas confirms the view that these genera are probably among the oldest in the Carduinae.
Several evolutionary trends within the Carduinae have been pointed out by putting the resulting cladogram into a geographical, ecological and cytological context:
1. Two main centres of diversification are assumed: (1) a Mediterranean-SW Asian centre, in which the Carduus-Cirsium group is most diverse, and (2) a Central Asian-Himalayan centre, in which the basal Centaureinae genera Serratula and Stemmacantha as well as the genera in the sister group of the Centaureinae have evolved. It is concluded that the large subtribe Centaureinae with its almost world-wide distribution has originated in Central Asia.
2. The genera in the Central Asian clade occur predominantly in subalpine and alpine habitats, whereas in the Mediterranean complex, a wider ecological range can be observed. 3. Genera which are mainly restricted to mountain areas show no apparent adaptations to long-distance dispersal of the achenes. This trend is interpreted as a minimization of risk by concentrating the reproductive effort in maintaining the growth site in adverse environments. Structures which preclude long-distance dispersal of achenes are e.g. a fragile pappus or length reduction of pappus bristles. Some widespread groups among the Carduinae have developed efficient mechanisms for long-distance dispersal: among the most important are wind dispersal through a plumose pappus, myrmecochory through elaiosomes and epizoochory through sticking to animals by a viscous pericarp or by capitula with hooked involucral bracts. 4. The ancestral chromosome number within the Carduinae is possibly n = 18, which can be reduced to a base chromosome number of 9. The chromosome numbers n = 17 and n = 13, which are most common in the Carduinae, have probably arisen by aneuploid reductions from n = 18. The systematic recommendations which are drawn from the present analysis mainly concern the status of small genera. Some genera are easily attributable to larger groups. It is suggested that these genera should be critically addressed in future taxonomic treatments. The retention of the genus status of some isolated relictual genera such as Ancathia and Lamyropappus (formerly included in Cirsium), Alfredia and Olgaea (sometimes included in Carduus) and Dolomiaea (sometimes included in Jurinea) is recommended.