Systematics of Iochrominae (Solanaceae): Patterns in Floral Diversity and Interspecific Crossability

Iochrominae is a florally diverse clade of 34 Andean species and six traditionally recognized genera within Physaleae. Recent phylogenetic estimates suggest that four of the six traditional genera of Iochrominae are not monophyletic. Using this phylogenetic framework, we examine the evolution of floral morphology and interspecific crossability in Iochrominae. Iochrominae is inferred to have had ancestrally a purple corolla, but now manifests a wide range of colors (red/orange, yellow, green, purple or white), several of which appear to have arisen multiple times. Other floral traits traditionally employed in taxonomy, including corolla shape, corolla length, and stapet form, are similarly evolutionarily labile and homoplasious within Iochrominae. To explore the extent of post-pollination reproductive isolation in the group and assess the potential for hybridization in nature, we conducted greenhouse crosses among seven species of Iochrominae representing five traditional genera. Of 21 reciprocal pairwise crosses, only two failed to yield viable seed. While the crossability index (a measure of successful seed set and germination) varied among crosses, it correlated only loosely with degree of relatedness. These results suggest that the speciation and diversification of Iochrominae has not been accompanied by the formation of strong barriers to pollen receipt or early seed maturation. However, pre-mating factors, such as allopatry and ethological isolation, and post-germination factors, such as reduced hybrid fitness, might have together acted to maintain the morphological and evolutionary cohesiveness of Iochrominae species