Capitulum compartmentalization in Leucheria (Nassauvieae): Insights into the evolution of Asteraceae inflorescence

Abstract

An unusual feature occurs in the capitula of Leucheria (Nassauvieae, Asteraceae), some phyllaries of the involucre are twisted and/or rotated. The different spatial orientations of these phyllaries, called here paleaceous phyllaries, divide the capitulum into compartments enclosing florets and fruits. Because the internal morphology of the phyllaries could play a role in the compartmentalization, the anatomy of the phyllaries together with their different spatial arrangements was analyzed in the 49 species of Leucheria. We found differences between the abaxial and adaxial epidermis, bulliform-like cells in the epidermis, and a callus at the base of the phyllaries. Cohesion, swelling, and turgor mechanisms in tissues are proposed to play a role in the positional changes of the phyllaries. The phyllaries bend, twist, rotate, and spread down and, excepting the latter, all are involved in capitula compartmentalization. The paleaceous phyllaries are already present in buds and continue during the whole plant life. Our results support previous phylogenetic hypotheses that suggest that Leucheria achieved a regular capitulum but maintained the remnants of an ancestor's pseudocephalium.

Exceptional evolutionary lability of flower‐like inflorescences (pseudanthia) in Apiaceae subfamily Apioideae

“…This mechanism could potentially explain why among apioids pseudanthia are common in many montane or arid‐adapted species, such as representatives of the genera Tordylium , Echinophora , Dicyclophora , or Pleurospermum . Interestingly, similar secondarily compartmented or aggregated inflorescences (syncephalia) occurring in Asteraceae subtribe Nassauvinae are also considered an adaptation to dry habitats (Katinas et al, 2008; Katinas and Forte, 2020).…”

A Synopsis of Leucheria (Asteraceae, Nassauvieae), with Notes on the Morphology

“…However, these features very often show variation in the same species or in the same individual. Katinas and Forte (2020) analyzed the phyllaries of the involucre in detail and concluded that most species of Leucheria have both regular capitula and capitula with paleaceous phyllaries, demonstrating that this character is too variable to be useful for classification purposes. They concluded that in the course of the tribe's evolution, Leucheria achieved what looks like a regular capitulum, but with the remnants of an ancestral secondary head evidenced in the paleaceous phyllaries and in the capitulum compartmentalization.…”

“…In the capitula with paleaceous phyllaries, the outer and inner phyllaries can bend, twist, and rotate, generating a capitulum compartmentalization where one or more florets are separated from other florets by the phyllaries (Figure 5B). The anatomy of the phyllaries was studied in detail by Katinas and Forte (2020), showing differences between the abaxial and adaxial epidermises of the phyllary, bulliform-like cells in the epidermis, and a callus at the base of the phyllary.…”

“…They are perennial acaulescent or caulescent herbs, sometimes suffruticose, with bilabiate corollas, tailed anthers, truncate styles with a crown of collector trichomes at the apex, and a plumose pappus (Figure 1A-G). Most species have a unique feature in the Nassauvieae, which is the curious disposition of some phyllaries of the involucre, called paleaceous phyllaries (Katinas and Forte 2020). The phyllaries bend, twist, and rotate at angles up to 180°, generating an internal division or compartmentalization of the capitula (Figure 1H,I).…”

Revised molecular phylogenetic analysis of Leucheria Lag. sensu lato (Asteraceae; Nassauvieae) and implications for morphological and ecological evolution

“…In this case, Pérez2020 used the Jara2017 topology with nine terminals removed. The Jara2017 topology also was reproduced by Katinas & Forte (2020) to map evolution of inflorescence characteristics in the genus. While Lavandero2020 reported topological disagreements between their reanalyzed phylogeny and that used in Pérez2020 (including Lavandero), they did not comment (then or since) on the implications for Pérez2020's results, which would be highly sensitive to both topology and branch lengths.…”