Disentangling confusions in inflorescence morphology: Patterns and diversity of reproductive shoot ramification in angiosperms

Abstract

Terminology of inflorescence diversity has often been used in a confusing way in the literature, partly because it was based on uncritical and outdated definitions. In particular, the terms cyme, thyrse, and panicle have been misused. Although a more critical classification worked out by several authors is available, it is unfortunately not in general use because most of the relevant publications are written in German. In addition, some terms have not been used in the same way by morphologists and developmental geneticists. The present review attempts to remedy the situation with a simple outline of a classification based on: (i) different branching patterns; (ii) differential elongation of axes of different orders; and (iii) repetition of basic ramification patterns in different ways. Racemose and cymose branching are two extreme patterns; the former with limitation of axial orders to two, the second with limitation of lateral axes of each order to two. In a branching system, a sequence of racemose → cymose and, within the cyme, of dichasial → monochasial is common, but the reverse sequence generally does not occur. Systematic and evolutionary aspects of inflorescences are briefly discussed. Branching patterns are often stable in larger clades. Inflorescences of mutants studied in developmental genetic studies are mainly altered in flower or branch numbers or relative branch length, but not in branching patterns. This is also a contribution towards the goal of a unified terminology for the different fields of biology dealing with inflorescences. Key words branching patterns, cymose, inflorescence, panicle, racemose, reproductive shoot, thyrse.Whereas flowers have been in center of interest in many branches of plant science, including morphological, developmental, functional, biological, ecological, and evolutionary aspects, inflorescences have received much less attention. Except for the studies by W. Troll and collaborators (e.g. Troll & Weber, 1953, 1955Troll, 1957Troll, , 1964Troll, , 1969Weberling, 1965Weberling, , 1989aTroll & Weberling, 1989;Weberling & Troll, 1998), no broad critical comparative morphological studies on inflorescences were undertaken in the past century. Because Troll's works were published in German, they did not get proper attention at a world scale. The most recent, but now rather dated, general treatments of morphological inflorescence classification by an author writing in English were provided by Rickett (1944Rickett ( , 1955. He used the presence or absence of terminal flowers, branching patterns, relative branch length, and the sequence of flower opening in an inflorescence as important criteria for a basic inflorescence classification. However, branching patterns and sequence of flower opening involve two very different realms of development; the first deals with initial stages of branching, the second with

Integrating Early Cretaceous Fossils into the Phylogeny of Living Angiosperms: ANITA Lines and Relatives of Chloranthaceae

“…Because female inflorescences are unknown, we score inflorescence type (42) based on the male structures, which we interpret as spikes of unistaminate flowers (as did Friis et al 2006Friis et al , 2011, but inflorescence partial units (43) as unknown, because the female flowers may or may not have been borne in cymose units, as in Hedyosmum (which has male spikes and female thyrses, both included in the same state of character 42). Contrary to earlier authors (Endress 1987;Todzia 1988;Eklund et al 2004;Endress and Doyle 2009), Doria et al (2012) interpreted the partial units in female inflorescences of Hedyosmum as spikes, rather than monochasial cymes. Under this hypothesis, the total number of bracts within and subtending each unit should be one more than the number of flowers.…”

“…Friis et al (2001) interpreted all floral parts as whorled, but on more critical examination Friis et al (2009) were unable to detect either orthostichies or clockwise and counterclockwise parastichies that are inclined at different angles, which would indicate whorled or spiral phyllotaxis, respectively (Endress 2006;Endress and Doyle 2007). Based on these observations and the absence of Fibonacci numbers, they concluded that phyllotaxis was probably not spiral, but whorled phyllotaxis could not be established either.…”

“…The extant genera are known for their extremely simple flowers: unisexual flowers consisting of either one stamen or one carpel in Ascarina, or one stamen or one carpel with three tepals at the top (so the ovary is inferior) in Hedyosmum, or bisexual flowers consisting of one carpel and one stamen or a problematic three-lobed androecium, respectively, in Sarcandra and Chloranthus (Swamy 1953;Endress 1987). Doria et al (2012) interpreted the ovary of Hedyosmum as superior, but as discussed in the section on the Asteropollis plant, this is incorrect.…”

“…However, three positions within Chloranthaceae are only one step less parsimonious: sister to Hedyosmum, Ascarina, and the ASC clade. The third position is less parsimonious than it was in Eklund et al (2004) because we rescored the tegmen character (132) in Chloranthus as uncertain (Doyle and Endress 2010): a fibrous exotegmen like that of Ascarina occurs in Chloranthus erectus, one of the two species studied, but not in Chloranthus spicatus (Corner 1976;Endress 1987). Positions outside the chloranthaceous line are at least two steps worse.…”

“…The flowers were first figured by Friis et al (1994) and associated with the pollen by Friis et al (1997bFriis et al ( , 1999, who pointed out their similarity to Hedyosmum. As in Hedyosmum, the female flower consists of one carpel with three tepals on top and three window-like depressions on the sides, while the male axes are also like those of Hedyosmum, in which the individual stamens are interpreted as unistaminate flowers with no perianth or subtending bracts (Endress 1987;Eklund et al 2004). Eklund et al (2004) analyzed the phylogenetic position of this plant based on the female flowers and pollen alone, because of uncertainty that the male structures were associated, but this association is now well established (Friis et al 2006(Friis et al , 2011.…”