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. 2012 Jan;109(1):127-34.
doi: 10.1093/aob/mcr240.

An extinct Eocene taxon of the daisy family (Asteraceae): evolutionary, ecological and biogeographical implications

Viviana D Barreda  1 , Luis Palazzesi, Liliana Katinas, Jorge V Crisci, María C Tellería, Kåre Bremer, Mauro G Passalia, Florencia Bechis, Rodolfo Corsolini
Affiliations

An extinct Eocene taxon of the daisy family (Asteraceae): evolutionary, ecological and biogeographical implications

Viviana D Barreda et al. Ann Bot. 2012 Jan.

Erratum in

  • Ann Bot. 2012 Feb;109(2):491. Passala, Mauro G [corrected to Passalia, Mauro G]

Abstract

Background and aims: Morphological, molecular and biogeographical information bearing on early evolution of the sunflower alliance of families suggests that the clade containing the extant daisy family (Asteraceae) differentiated in South America during the Eocene, although palaeontological studies on this continent failed to reveal conclusive support for this hypothesis. Here we describe in detail Raiguenrayun cura gen. & sp. nov., an exceptionally well preserved capitulescence of Asteraceae recovered from Eocene deposits of northwestern Patagonia, Argentina.

Methods: The fossil was collected from the 47·5 million-year-old Huitrera Formation at the Estancia Don Hipólito locality, Río Negro Province, Argentina.

Key results: The arrangement of the capitula in a cymose capitulescence, the many-flowered capitula with multiseriate-imbricate involucral bracts and the pappus-like structures indicate a close morphological relationship with Asteraceae. Raiguenrayun cura and the associated pollen Mutisiapollis telleriae do not match exactly any living member of the family, and clearly represent extinct taxa. They share a mosaic of morphological features today recognized in taxa phylogenetically close to the root of Asteraceae, such as Stifftieae, Wunderlichioideae and Gochnatieae (Mutisioideae sensu lato) and Dicomeae and Oldenburgieae (Carduoideae), today endemic to or mainly distributed in South America and Africa, respectively.

Conclusions: This is the first fossil genus of Asteraceae based on an outstandingly preserved capitulescence that might represent the ancestor of Mutisioideae-Carduoideae. It might have evolved in southern South America some time during the early Palaeogene and subsequently entered Africa, before the biogeographical isolation of these continents became much more pronounced. The new fossil represents the first reliable point for calibration, favouring an earlier date to the split between Barnadesioideae and the rest of Asteraceae than previously thought, which can be traced back at least 47·5 million years. This is the oldest well dated member of Asteraceae and perhaps the earliest indirect evidence for bird pollination in the family.

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Figures

Fig. 1.
Fig. 1.
Simplified geological map of north-western Río Negro Province showing the fossil locality (41°09′26·06′′S, 70°49′57·11′′W, WGS84). Modified from Giacosa et al. (2001).
Fig. 2.
Fig. 2.
Stratigraphic section of the Huitrera Formation at the Río Pichileufú flora site, showing the location of the fossil-bearing levels.
Fig. 3.
Fig. 3.
Raiguenrayun cura gen. and sp. nov., fossil Asteraceae from north-western Patagonia, southern South America. (A) General view of the cymose capitulescence-like fossil showing two long-pedunculate head-like inflorescences. (B) Detail of the central capitula. Arrowheads show involucral bracts. (C) Capitulescence under fluorescent light taken with a confocal microscope. Note the slender projection (bract?) in the peduncle of the lateral capitula (arrowhead). (D) Apical zone of the central capitula showing individual florets (arrowheads). (E) The same detail of D, but under fluorescent light. Note the shining slender projections (pappus) among florets. Scale bars = 1 cm.
Fig. 4.
Fig. 4.
Reconstruction of a hypothetical ancestral Asteraceae based on morphological features of both the fossil Raiguenrayun cura gen. & sp. nov. and the morphologically closest extant tribes.
Fig. 5.
Fig. 5.
Extant member of an early branching lineage of Asteraceae (Mutisioideae), Cnicothamnus lorentzii Griseb., that superficially resembles the Patagonian fossil capitula.
Fig. 6.
Fig. 6.
Modified meta-tree of Funk et al. (2009) with the inclusion of the fossils Raiguenrayun cura gen. & sp. nov. and Mutisiapollis telleriae (dashed-dotted lines). In grey: taxa that share more characters with R. cura and M. telleriae than any other extant member in Asteraceae. Some branches are not well supported as compared with the remainder of the tree (dashed lines; Funk et al., 2009). Crown group, stem group and stem representative definitions are based on Magallón (2004).
Fig. 7.
Fig. 7.
Mutisiapollis telleriae, fossil pollen grain from the capitula-bearing sample. (A) General view, focus on well-developed spines (arrowhead). (B) Focus on exine structure (arrowhead). Specimen on slide MLG 1156: co-ordinates J51/J52. Scale bars = 10 µm.
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