Systematics and biology of the nightshade family
THE NIGHTSHADE FAMILY
There are almost 3000 species in the nightshade family, Solanaceae. Nearly half of them are found in the genus Solanum, including e.g. potato, tomato, eggplant. The highest species diversity is found in Central and South America.
Characteristics of the family
Leaves are generally alternate and lack stipules. The flowers have five stamens and one style and ovary with two carpels. The flowers have sympetalous corollas. The fruit is most often a berry or a follicle with many seeds.
The nightshade family includes annuals, climbers, epiphytes, shrubs as well as tree and they are present in all kinds of habitats, from deserts to tropical rain forests.
A berry is a fleshy fruit type where all layers are soft, as in e.g. tomato, Cape gooseberry or eggplant. The fruit often change colour when ripening. The seeds are generally dispersed when animals eat the whole fruit. Remember that some fruits might be very poisonous to humans even if they are eaten by other animals. This is the case with e.g. the fruits of deadly nightshade Atropa belladonna.
A follicle is a dry fruit type that opens up to disperse its seeds, as in e.g. petunias, tobacco or thornapple. The fruits persist on the plant and the seeds are dispersed by wind or passively by animals. Some follicles opens explosively and the seeds are projected.
POLLINATION IN SOLANACEAE
There is a great diversity of pollinators in the family. Many species with open flowers are visited by bees, whereas species with flowers with long corolla-tubes are visited by hummingbirds, moths or butterflies in their natural habitats.
Scent and colour matters
Birds can see the colour red, but have a poor sense of smell. Insects can not see red, but can see ultraviolet (UV). Moths are attracted by strong sweet scent and can more easily spot white flowers in the dark.
A typical hummingbird pollinated flower has a long tube, is often red colour, sometimes has protruding stamens and loads of nectar, but lack scent.
A typical moth pollinated flower also has a long tube, but is often white in colour and has a strong smell (especially during the night). Some species close their flowers during the day to minimise visits of unwanted visitors that are unable to perform a proper pollination.
Close relatives, different pollinators
There are examples of closely related species both in the genus Nicotiana and the genus Petunia that have completely different pollinators. For example Langsdorff's tobacco lack scent and is visited by hummingbirds, but woodland tobacco has a strong scent during the night and is visited by moths. The same goes for the large white petunia, whereas many other species of Petunia have less scent and are pollinated by bees. It has been shown that the existence of scent in this case is regulated by one single gene.
Many species in the Solanaceae family have anthers with specific pores. The pores open and release pollen only when exposed to vibrations at a certain frequency. For example are bumble bees perfectly adapted to pollinate tomato flowers in this way. They grab the flower with its legs and vibrate vigorously using their flight muscles to release pollen.