Inflorescence diversity and evolution in the PCK Clade (Poaceae: Panicoideae: Paniceae)

Abstract

The PCK Clade, represented by six to nine genera, is a monophyletic group situated within the Paniceae tribe. The highly diverse inflorescences within the PCK Clade provide an interesting system for the study of morphological evolution and also may aid in better understanding its unclear systematics. The inflorescence structure of 110 members of the PCK Clade has been investigated. Inflorescences are polytelic showing different levels of truncation. At least 21 different inflorescence subtypes were identified. Fourteen variable inflorescence characters were found, among which some have suprageneric or infrageneric value and others are polymorphic.A key for the identification of inflorescence types is presented. Nine processes have been identified as responsible for inflorescence diversification. Highly branched inflorescences with different internode lengths are present in the basal genus whereas truncated inflorescence morphologies appear late in the history of the clade. The precise timing of morphological changes is impossible to assess until we have a well supported phylogeny for the PCK Clade.

Inflorescence structure in Rhynchospora Vahl (Cyperaceae)

“…Partial homogenization of the distal portion of the inflorescence, is recognized here for first time in Cyperaceae -but with structural differences in comparison with Poaceae, were partially homogeneous inflorescences present a distal homogeneous region and a proximal non-homogeneous region (Reinheimer and Vegetti, 2008;Rua, 1996;Rua and Weberling, 1998). In Rhynchospora, partially homogeneous inflorescences have two homogeneous regions separated by a middle non-homogeneous region (Fig.…”

“…In non-homogenized inflorescences branches present different degrees of ramification along the inflorescence and do not present specialization, while in the fully homogenized inflorescences the degree of ramification is the same for all branches (Rua, 1996(Rua, , 1999Troll, 1964;Weberling, 1985Weberling, , 1989. When homogenization is only partial, some branches present similar branching degree and other have a different branching degree (Reinheimer and Vegetti, 2008;Rua, 1996Rua, , 1999. The resulting inflorescence has been considered in Poaceae as a transitional or intermediate form between the non-homogeneous inflorescence and a fully homogeneous inflorescence (Reinheimer and Vegetti, 2008;Rua, 1996;Rua and Weberling, 1998).…”

“…When homogenization is only partial, some branches present similar branching degree and other have a different branching degree (Reinheimer and Vegetti, 2008;Rua, 1996Rua, , 1999. The resulting inflorescence has been considered in Poaceae as a transitional or intermediate form between the non-homogeneous inflorescence and a fully homogeneous inflorescence (Reinheimer and Vegetti, 2008;Rua, 1996;Rua and Weberling, 1998). Partially homogenized inflorescences were never recognized in Cyperaceae so far.…”

“…Truncation consists in loss of the distal portion of the inflorescence. Homogenization is the specialization of distal portions of the inflorescence in such a way that the lateral branches become homogeneous throughout (Rua, 1999), producing similarities in the ramification degree among the inflorescence branches (Reinheimer and Vegetti, 2008). In non-homogenized inflorescences branches present different degrees of ramification along the inflorescence and do not present specialization, while in the fully homogenized inflorescences the degree of ramification is the same for all branches (Rua, 1996(Rua, , 1999Troll, 1964;Weberling, 1985Weberling, , 1989.…”

Inflorescence Structure

“…The fate of the inflorescence meristem often varies among closely related species (see, for example, Kellogg et al 2013;Reinheimer and Vegetti 2008;Reinheimer et al 2009), suggesting that it may be relatively easy to shift in evolutionary time, a point also made by Butzin (1979). The fate of the inflorescence meristem is independent of that of the primary-, secondary-, and higherorder branches, which may also terminate in spikelets or not.…”