Early floral development and androecium organization in the sarracenioid clade (Actinidiaceae, Roridulaceae and Sarraceniaceae) of Ericales

Abstract

The early floral development of Actinidia (A. arguta, A. callosa, A. chinensis and A. kolomikta; Actinidiaceae), Saurauia (S. montana, S. oldhamii, S. pittieri and S. subspinosa; Actinidiaceae), Roridula gorgonias (Roridulaceae) and Heliamphora nutans (Sarraceniaceae) was studied comparatively using scanning electron microscopy. Late stages of androecium development are additionally presented for Clematoclethra scandens (Actinidiaceae), Darlingtonia californica and Sarracenia leucophylla (Sarraceniaceae). Flowers are typically pentamerous and share a number of developmental features: perianth organs emerge in a clockwise or anticlockwise spiral sequence on the floral apex with relatively long plastochrons between successive organs, resulting in conspicuous size differences among perianth organs in early development; the perianth always consists of two differentiated whorls (unlike earlier interpretations of the perianth in Heliamphora); the androecium is polystemonous in most species and is initiated with leading stamens in alternipetalous positions; successive stamen primordia appear in a lateral succession until a ring‐like structure is formed; and the anthers become inverted shortly before anthesis. Later androecial development differs conspicuously between taxa and further proliferation may be centrifugal, centripetal and/or lateral. For Ericales, unusual features of floral development include: petals initiated in a spiral sequence (but later organized in a whorl) with comparatively long plastochrons between individual petals (except Saurauia); common occurrence of perianth organs in double positions in Actinidiaceae; and anthers that become inverted close to anthesis. The floral development in the sarracenioids is additionally compared with that of other families and clades in Ericales, further emphasizing the highly variable patterns of androecium development in the order.

How (much) do flowers vary? Unbalanced disparity among flower functional modules and a mosaic pattern of morphospace occupation in the order Ericales

“…flowers with more stamens than perianth organs) has apparently evolved along several separate lineages in Ericales [ 35 ]. In addition to the diversity in stamen numbers, ontogenetic patterns of androecium development and anthetic stamen arrangement are also particularly diverse in Ericales, including complex ring primordia with multiple stamen whorls and stamens arranged in fascicles [ 82 ]. With the exception of early diverging angiosperms, there are probably only few other groups of angiosperms with such labile and diverse patterns of stamen numbers and arrangement as the Ericales.…”

Phylogeny of Coussareeae (Rubioideae, Rubiaceae)

“…On the other hand, detailed micromorphological studies (e.g., light microscopy of microtome sections and scanning electron microscopy), ontogenetic studies, and further palynological studies may reveal further synapomorphies. An example where studies such as these revealed multiple synapomorphies for a seemingly morphologically disparate clade is the (Sarraceniaceae-(Actinidiaceae-Roridulaceae)) clade in Ericales (Löfstrand and Schönenberger 2015;Löfstrand et al 2016). Hence, the three major suprageneric clades could be recognized at the tribal level, but we refrain from performing any nomenclatural changes at present, pending detailed micromorphological studies of Coussareeae as currently delimited.…”

Profile of a flower: How rates of morphological evolution drive floral diversification in Ericales

“…This was largely due to high levels of floral diversity and disparity exhibited by Ericales (Figure 1). Flowers in Ericales may be zygomorphic (e.g., Balsaminaceae; Figure 1I) or actinomorphic (e.g., Actinidiaceae; Figure 1F), show various forms of polystemony (e.g., Lecythidaceae or Actinidiaceae; Figure 1D, F), or varying degrees of fusion between perianth parts (Schönenberger and Grenhagen, 2005; Schönenberger et al, 2010; von Balthazar and Schönenberger, 2013; Zhang and Schönenberger, 2014; Löfstrand and Schönenberger, 2015b; a; Löfstrand et al, 2016). Although the monophyly of Ericales is well-supported by numerous studies (Bremer et al, 2002; Soltis et al, 2011; One Thousand Plant Transcriptomes Initiative, 2019), the interfamilial relationships within the order have remained difficult to resolve(Anderberg et al, 2002; Schönenberger et al, 2005).…”

“…This was attributed to different selective regimes, varying degrees of module complexity, and developmental constraints influencing the flower modules in different ways. For example, multiple origins of polystemony and the apparent lability of androecium traits have been proposed as the main drivers of the high disparity found in the androecium (Schönenberger et al, 2005; Endress, 2011; Löfstrand et al, 2016; Chartier et al, 2017). Four families (Ericaceae, Lecythidaceae, Primulaceae, and Sapotaceae) were found to account for more than half of the disparity among Ericalean flowers (Chartier et al, 2017).…”