Probably the best-behaved of the many climbing annuals, these delightful flowers will brighten any trellis
The genus thunbergia is best known for its climbers, though there are a few lax shrubs too. Some of the perennial climbers are nothing short of fabulous and the lilac-blue T. grandiflora, though an unwanted invader in warmer climates, is a gorgeous thing while T. mysorensis has large, gaping yellow and red flowers, hanging below the foliage. These are just dreams for me but T. alata is a tender perennial that can be grown as an annual. Thunbergias are largely from Eastern Africa and India and the genus is named after the Swedish botanist Carl Peter Thunberg, not the serial school truant.
Thunbergia alata is a twining climber with large, typically orange flowers with black centres, leading to the common name of black-eyed Susan. The large, round seeds can easily be sown, two or three to a pot, in March at 20c and readily germinate and, with plenty of light, grow quite quickly, ready to be planted out after the last frost. Although plants can reach 1.5m in a season they are best grown in really good soil in a sheltered place or in patio containers. They will flower all summer and into autumn. Without support they scramble sideways and they are often recommended for hanging baskets though they tend to climb up the chains rather than form a cascade of blossom. In theory these are perennials but they are almost always grown as annuals here.
Much work has been done to expand the colour range and as well as white. There is also a range of orange shades and now pinks, although these seem to be sold as plants and I do not think the pinks are available as seed.