We all like eating tomatoes and potatoes - what could be better than chips with ketchup ! But did you know tomatoes and potatoes are extremely closely related? Although a red juicy tomato looks totally different to a pale yellow potato, the two plants share much of their DNA.
Potato and tomato belong to a group of plants known as Solanaceae - the nightshade family. In actual fact, they are so closely related they belong to the same genus within Solanaceae, known as Solanum. Tomato is called Solanum lycopersicum L. in scientific latin, whilst potato is known as Solanum tuberosum L.
Other well known species in the group include the bell peppers, chili peppers, eggplants, petunias, and tobacco - yes, incredibly this strongly flavoured plant is related to commonly eaten yummy things! South Americans might know more fruits from the family, such as naranjilla (Solanum quitoense Lam.), or tamarillo (Cyphomandra betacea Sendt.) used for making preserves and juice. If you visit Mexico and indulge in local food culture, you come across another species from the family, tomatillo (Physalis philadelphica Lam.) which is used to prepare salsa for buritos, tacos and tortillas.
Below is a lovely phylogeny of the nighshades which illustrates how the species are related within the family. It's based on a small set of DNA data. It is still not complete as it only includes roughly 30% of all the species in the family. Our aim is to add more species as our research progresses. What you can see is that eggplant, tomato, potato and pepino are really closely related, and tobacco is the furthest relative of them all. 
The nightshades were known to be a group of closely related plants before anybody even knew they are related based on their DNA. This is because all species in the group share a set of morphological characters. Some of these are very obvious such as flowers which are generally stellate, with five corolla lobes, and five stamens. The most clear character that unites the family is seeds. Seeds are small – think of tomato seeds! – flattened, kidney-shaped, and have puzzle-piece shaped cells if looked under a microscope. Most of seeds in the nightshade family have curled embryos. If you are curious, try looking at dried tomato seeds closely! You will see the impression of the curled embryo on the seed quite easily.
Other characters of the nightshade family are more hidden. For example, all nightshades have internal phloem which means that sugars produced in leaves via photosynthesis are transported down to roots inside the water transport system known as xylem. Most plants have an opposite type transport system where sugars are transported outside the waterpipe system.
Anyways, why all this ramble? Well, the thing is that we are about to go hunting for nightshades in the Andes! There are an estimated 4,500 species of nightshades in the world, and large number of these is found in the Andes. These are wild relatives of tomatoes and potatoes and such likes, some weirder than other, some with tubers, whilst other climb trees! There are still species remaining to be described, waiting in the forests and mountain sides for discovery. We will be travelling in the northern part of Argentina and in Peru over the next coming 3 months – our aim is to collect as many species of Solanaceae on our way. This time we are targeting the particularly poorly known species of the Morelloid clade in the genus Solanum, a set of roughly 60 species.
