Incidimos en algunos aspectos epistemológicos básicos de las dos metodologías de análisis con da-tos de secuenciación en Sistemática Molecular: parsimonia y máxima verosimilitud. El hecho de que el árbol filogenético verdadero sea desconocido e irreconocible hace que la posición representada por la parsimonia sea actualmente la única herramienta epistemológicamente válida para obtener una topolo-gía de relaciones refutable. Aunque las aproximaciones de máxima verosimilitud no parecen aplicables a la selección de un árbol filogenético, sí pueden proporcionarnos hipótesis referentes a los datos utilizados para construir esas topologías de relaciones. Sería deseable un marco híbrido de análisis sistemático molecular que permitiera usar el poder predictivo de las inferencias probabilísticas basadas en los datos para dirigir el criterio de decisión de la parsimonia.

We highlight some basic epistemological aspects of the two analytical methodologies for sequence data in Molecular Systematics: parsimony and maximum likelihood. The fact that the true phylogenetic tree is unknown and non-recognizable brings out parsimony as the only current epistemologically valid tool to choose a refutable topology of relationships. Although maximum likelihood approaches do not seem applicable to selecting a phylogenetic tree, they can provide us with hypotheses referring to the data used to build those topologies of relationships. A hybrid analytical framework for molecular systematics that used the predictive power of probabilistic inference based on data to tailor the decision criterion of parsimony would be desirable.

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We examined patterns of cpDNA RFLP variability using 21 restriction endonucleases in 21 populations of Androcymbium that represent 12 endemic species distributed in the winter rainfall areas of South Africa to explore the diversification of the genus in its area of maximum species diversity. Our results are supportive of a diversification landscape characterized by continued opportunistic short-range invasion, naturalization, and rapid speciation, in which the selective action of the different environments where Androcymbium species occur determined their colonization success and subsequent short-range geographic expansion. The historical presence of fire, the constraint imposed by the low concentration of nutrients throughout southwestern South Africa and the different reproductive capabilities of Androcymbium species have also likely stimulated species’ diversification. Our divergence time estimates bolster theview that speciation of South African Androcymbium initiated in the late Eocene, intensified in the Oligocene and proceeded more sporadically during the Miocene. These chronological estimates alsosubstantiate the previous hypothesis that most lineages of Androcymbium in South Africa are much more ancient than their North African relatives, whose diversification began in the late Miocene-early Pliocene.

The cpDNA restriction variation in 39 populations representing a geographical sampling of 18 species of Androcymbium in southwestern and northern Africa was examined to assess the historical biogeography of the genus. The cpDNA phylogeny indicates that the disjunction between South and North Africa is best explained by the dispersal of southern African ancestors into North Africa. Divergence time estimates suggest that the geographic range of the genus may have extended considerably north (perhaps to Tanzania and Kenya) prior to the global desiccation of Africa in the Miocene. Further expansion of the genus northward was probably stalled until climatic changes in the late Miocene brought about the gradual replacement of a subtropical woodland savanna with the arid landscape that gave rise to the Sahara. Aridification of the northern quarter of the continent provided the ecological conditions for fostering the expansion of Androcymbium along the Mediterranean fringe (probably east to west) and its introduction into the Canary Islands. Unlike their South African congeners, the northern species have experienced expansions, fragmentations, and local extinctions in response to the severe climatic shifts in thisarea during the Pliocene-Pleistocene. According to our divergence time estimates, the arid track may have already existed as a continuous area connecting southern and northern Africa in the late Miocene.