Morphological trait evolution in Solanum (Solanaceae): Evolutionary lability of key taxonomic characters

Abstract

Solanum is one of the world's largest and economically most important plant genera, including 1245 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 >100 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.…”

“…( A ) Phylogeny (reproduced from https://lifemap-ncbi.univ-lyon1.fr/) and corresponding images of representative vascular plants that independently evolved prickles. Number in parentheses indicates number of identified independent evolutionary origins of prickles ( B ) Phylogenetic tree [adapted from ( 9, 10 )] of the spiny Solanum (subclades Wendlandii, Nemorense, and Leptostemonum) with species having lost prickles highlighted in red. Representative images of narrow and broad-based prickle morphologies are shown.…”

“…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.…”

HD-Zip proteins modify floral structures for self-pollination in tomato

“…This could provide an advantage during evolution or be deliberately selected in domestication. The mechanism identified in tomato could also be applied to many other plant species with anther cones in nature ( 14 , 33 ).…”

“…The transition from anisogamy to complete cleistogamy in tomato was thought to have been achieved by the elimination of self-incompatibility (SI) ( 7 – 9 ) and stigma shortening (mutations in the Style2.1 and SE3.1 genes) ( 10 , 11 ). However, as shown in other Solanaceae species such as peppers and eggplants, stigma-shortening and self-incompatibility release alone are not sufficient for the establishment of cleistogamy ( 12 – 14 ). Tomato flowers develop a morphological feature known as the “anther cone”, in which five anthers join together to form a hollow tube-like cone around the style.…”