Commemorating Lord Robert James Petrie (1714–43) of Thorndon, Suffolk, UK, owner of one of the finest collections of exotic plants in Europe, overseen by Philip Miller.

Trees, shrubs and climbers. Leaves opposite or whorled, simple, entire, deciduous to evergreen. Flower clusters axillary or terminal, indefinite, elongated. Flowers regular. Calyx usually ribbed. Corolla darker than the calyx, slightly asymmetric. Fruit a drupe, with persistent swollen calyx, splitting into 2 parts, each with 1 seed.

Grown as P. volubilis for the spectacular clusters of flowers and architectural leaves, mostly in warmer climates but will survive Melbourne temperatures in a sheltered position.

Semi-hardwood cuttings, layers.

Spectacular long, lax, cylindrical clusters of indigo flowers in the cultivated species.

30 species from tropical America and Mexico. L

Moldenke (1938), Rueda (1994).

Source: Spencer, R. (2002). Verbenaceae. In: Spencer, R.. Horticultural Flora of South-eastern Australia. Volume 4. Flowering plants. Dicotyledons. Part 3. The identification of garden and cultivated plants. University of New South Wales Press.