Phylogenetic, biogeographical, and morphological diversity of the Paronychia chartacea (Caryophyllaceae) clade from the Coastal Plain Floristic Province of North America

Development differs between independently evolved staminode whorls in the same flower

“…Under that hypothesis, dioecy would allow for allocation of energy because staminate plants are hypothesized to cover a more expansive area and produce more flowers, while carpellate plants produce fewer, more energy-dependent flowers (Bawa, 1980;Bell, 1985;Barrett and Hough, 2013). Furthermore, this hypothesis could also explain why staminate plants exhibit longer shoots in the two species (Anderson, 1991;Schenk and Appleton, 2021). A cursory examination of plants, however, has shown that staminate plants have fewer flowers than carpellate plants, making this hypothesis less likely, although the differences in the average number of flowers per plant will need to be quantified to formally test this hypothesis.…”

“…Most species in Paronychia are hermaphroditic, but two species have evolved unisexual flowers and are dioecious (Anderson, 1991; Schenk and Appleton, 2021). The hermaphroditic flowers of most species are described as bicarpellate with a single ovule reaching maturity, five petal‐like sepals, and a diplostemonous (pseudodiplostemonous, sensu Ronse De Craene et al, 1998) androecium that consists of a whorl of five antesepalous stamens that alternate with five alternisepalous staminodes (Figure 1; Ronse De Craene and Smets, 2001).…”

“…Plants with staminate flowers have been referred to as “male” (we hereafter refer to them as staminate), and those with carpellate flowers have been referred to as “female” (we hereafter refer to them as carpellate). What makes the two dioecious species even more remarkable is that they are sexually dimorphic, with staminate plants having more elongated internodes along the stems compared to carpellate plants (Anderson, 1991; Schenk and Appleton, 2021). Moreover, P. chartacea and P. minima are sister species (Schenk et al, 2018), so it is most parsimonious that unisexual flowers and sexual dimorphism first evolved in their most recent common ancestor rather than the two species evolving dioecy independently (Schenk and Appleton, 2021).…”

“…In carpellate flowers, stamens in antesepalous positions evolved into staminodes (Figure 1). Appleton and Schenk (2021) and Schenk and Appleton (2021) determined that the antesepalous staminodes independently evolved in carpellate flowers. Anderson (1991) characterized P. chartacea and P. minima (treated as subspecies of P. chartacea at the time) as polygamodioecious, with plants producing either staminate and hermaphroditic or carpellate and hermaphroditic flowers.…”

“…What makes the two dioecious species even more remarkable is that they are sexually dimorphic, with staminate plants having more elongated internodes along the stems compared to carpellate plants (Anderson, 1991;Schenk and Appleton, 2021). Moreover, P. chartacea and P. minima are sister species (Schenk et al, 2018), so it is most parsimonious that unisexual flowers and sexual dimorphism first evolved in their most recent common ancestor rather than the two species evolving dioecy independently (Schenk and Appleton, 2021). Charnov (1982) hypothesized that the presence of staminodes in hermaphroditic flowers could facilitate the transition to unisexual flowers, but this hypothesis remains untested.…”