The Evolution of Reproductive Characters in Dipsacales

Improved knowledge of Dipsacales phylogeny provides a solid framework for studies of character evolution. Although the polarity of many characters can now be confidently established, for others it remains unclear. This results largely from uncertainty about the broader relationships of Dipsacales and is especially problematic for characters that differentiate the two basal lineages, Adoxaceae and Caprifoliaceae. Within Caprifoliaceae, changes in stamen number became decoupled from corolla evolution, a reduction from five to four stamens, coinciding with the origin of the Linnina clade. Subsequently, there was a reduction to two stamens within Morinaceae and to three, two, and one within Valerianaceae. In contrast, within Adoxaceae, stamen number covaries with the number of corolla lobes, although the number of stamens was effectively doubled within Adoxina by the division of each stamen. Fleshy fruits may have evolved separately in Adoxaceae and in Caprifolieae. These vary in the number of seeds and in the presence or absence of an endocarp and show repeated patterns in the evolution of color, perhaps underlain by shifts in the timing of developmental events. In Caprifoliaceae, dry fruits include bicarpellate septicidal capsules in Diervilleae and initially tricarpellate, single-seeded achenes in Linnina. Achene fruits exhibit a variety of independently evolved dispersal mechanisms, especially involving modifications of the calyx lobes or bracts subtending the ovary. Within Linnina, a distinctive epicalyx surrounding the ovary appears to have originated through the fusion of supernumerary bracts. It is possible that the epicalyx evolved twice, once in the ancestor of the Morinaceae and again in the TriplostegiaDipsacaceae clade. Within the Dipsacaceae, modifications of the epicalyx parallel those of the ovary and calyx within Valerianaceae, suggesting a transference of function involving homeoheterotopy. Evolutionary adjustments of the epicalyx, calyx, and ovary wall in relation to protection and dispersal may have established an evolutionarily stable configuration.