Morphological trait evolution inSolanum(Solanaceae): evolutionary lability of key taxonomic characters

Abstract

Solanum L. is one of the worlds largest and economically most important plant genera, including 1,245 currently accepted species and several major and minor crops (e.g., tomato, potato, brinjal eggplant, scarlet eggplant, Gboma eggplant, lulo, and pepino). Here we provide an overview of the evolution of 25 key morphological traits for the major and minor clades of this giant genus based on stochastic mapping using a well-sampled recently published phylogeny of Solanum. The most evolutionarily labile traits (showing >150 transitions across the genus) relate to plant structure (growth form and sympodial unit structure), herbivore defence (glandular trichomes), pollination (corolla shape and colour), and dispersal (fruit colour). Ten further traits show evolutionary lability with 50-100 transitions across the genus (e.g., specialised underground organs, trichome structure, leaf type, inflorescence position and branching, stamen heteromorphism). Our results reveal a number of highly convergent traits in Solanum, including tubers, rhizomes, simple leaves, yellow corollas, heteromorphic anthers, dioecy, and dry fruits, and some unexpected pathways of trait evolution that could be explored in future studies. We show that informally named clades of Solanum can be morphologically defined by trait combinations providing a tool for identification and enabling predictive phylogenetic placement of unsampled species.

Convergent evolution of plant prickles is driven by repeated gene co-option over deep time

“…The clade encompassing all three of the cultivated eggplants diverged ~2 Mya, but prickles in Solanum are more ancient, having emerged over ~6 Mya, and 30 independent losses of prickles have been documented, including in additional domesticated and wild species (10). We tested whether mutations in PL underlie these repeated instances of prickle loss across this broader evolutionary timescale by sampling DNA from additional prickleless species and their prickled close relatives.…”

“…In the genus Solanum, which includes the major crops eggplant, potato, and tomato, prickles emerged in the common ancestor of the so-called "spiny Solanums" around 6 million years ago (Mya) (9,10). This lineage includes the large Leptostemonum clade, which comprises hundreds of globally distributed species, including all cultivated eggplants and their wild progenitors (Fig.…”

Twenty years of big plant genera

“…Do all big genera represent cases of synnovations [8] and confluences within lineages as has been shown for Astragalus [51] and to some extent in Solanum [52,53]?…”

“…[9]), and we are only limited by our imaginations. Do big genera represent adaptive radiations or lack of extinction?Do all big genera represent cases of synnovations [8] and confluences within lineages as has been shown for Astragalus [51] and to some extent in Solanum [52,53]?How do functional traits vary or covary within big genera? Does phenotypic plasticity play a role in diversification or life history in these species-rich lineages more or less than in smaller genera?Can controlling for phylogeny by using these big genera help to tease out processes that are lineage-specific versus more general characteristics in investigations of latitudinal gradients in functional traits (e.g.…”

A highly resolved nuclear phylogeny uncovers strong phylogenetic conservatism and correlated evolution of fruit color and size in Solanum L.

“…The genus Solanum L. comprises c. 1300 fleshy-fruited species and is the largest genera of Solanaceae and the second largest genus of fleshy-fruited plants (Frodin, 2004). Regarding fruit traits, Solanum shows a remarkably high diversity, producing berries of various sizes, colors, and pulp with different nutritional and chemical profiles (Cipollini et al, 2002;Knapp et al, 2004;Hilgenhof et al, 2023). For instance, berry size ranges between 0.5 and 20.0 cm, ripening in many colors, including black, purple, red, green, yellow, and orange.…”