A native of California, Mentzelia lindleyi is distinguished by stunning, bright yellow flowers 5cm/2in wide with glossy heart shaped petals. Numerous fine gold stamens cluster in the centre of each flower.

Ageratum houstonianum is a native of Mexico and is sometimes listed as A. mexicanum. It produces mounds of small, soft-looking, daisy-like flowers amid heart-shaped leaves.

Commonly known as snapdragon, Antirrhinum majus is a perennial usually treated as an annual, although in very favoured areas it may survive the winter.

Centaurea cyanus, the cornflower, is a sturdy border plant with blooms of pure blue, pink or white that make excellent cut flowers.

The most popular annual zinnia, Zinnia elegans, is native to Mexico; the vivid colours of its luxurious blooms certainly have an exotic air.

Salpliglossis sinuata is such an exotic-looking plant that it is difficult to believe it is so easy to grow - or that it belongs to the same family of plants as the potato.

The sweet pea, Lathyrus odoratus, climbs by means of leaf tendrils. Its wing-petalled flowers are coloured white, pink, red, lilac or cream, and are sometimes strongly scented. They are extremely popular as cut flowers.

Eschscholzia californica, the Californian poppy, is a dazzling candidate for the summer border, especially on dry soils. It blazes with colour - red, orange, yellow or pink - right through to the autumn.

Commonly known as the Livingstone daisy, Mesembryanthemum criniflorum is a succulent, low-growing plant best as informal edging for the summer border or in the rock garden.

The genus Salvia includes a number of species, among them the herbs sage and clary. S. splendens, a perennial grown as an annual, is an established favourite in summer bedding schemes, especially of the formal type.