Petrea volubilis, also known commonly as the sandpaper vine, Queen’s wreath or purple wreath, is a member of the Verbena family, Verbenaceae. It is a flowering climbing shrub that is grown for its beautiful blue flowers that are borne on pendulous racemes. Blue is a rare flower colour in the tropics and Petrea volubilis is considered by some gardeners as the substitute for the Wisteria in the tropics and subtropics. There is a version that bears white flowers which is rare and difficult to find.
Although this drought-tolerant plant will grow and flower without problems here in lowland Singapore, fellow local gardeners report that it is perhaps more rewarding to grow Petrea volubilis further up north of Malaysia and Thailand where there is a distinct dry season to induce more profuse flowering. The recent prolonged dry and hot spell in Singapore seemed to have triggered flowering in several potted specimens of Petrea volubilis located in NParks’ Pasir Panjang Nursery.
The genus name Petrea is derived from the name of Lord Petre who is a famous plantsman and collector of exotic plants in the 18th century. The specific name volubilis has the meaning of “twining”, which refers to the climbing habit of this plant. A candidate for growing in an outdoor garden in a location with full sun or semi-shade, Petrea volubilis is usually grown against a strong support. When there is no support, plants will twine around themselves and form a rounded shrub.
Each flower borne by Petrea volubilis has five, light blue and slender sepals which spread out almost equally like a star. The actual flower resides in the center of each of these star-like sepals. It is smaller but is quite impossible to miss when it opens as each flower is coloured with a more darker blue or purple colour. One will also notice a distinctive white spot on one of the petals.
The sepals are persistent, that is, they stay on the inflorescence for quite some time even after the flowers have faded. They will continue to possess the attractive light blue colour shortly after the flowers dropped off. However, in a rather gradual pace, these sepals will turn greyish as they age and finally become brown and dry before falling off. If the flowers have been pollinated earlier, each of these will bear a fruit capsule which is dispersed by the wind. The sepals take on the role of flight wings which assist in seed dispersal via wind. The sepals spin like a propeller when there is a breeze which help to keep the fruit in mid-air.
One may wonder why Petrea volubilis is called the sandpaper vine. It will only become apparent if one has access to the plant. This particular common name comes from the fact that the leaves of Petrea volubilis is rough to touch. The upperside of each leaf is rather coarse compared to the leaves of plants we usually come across.
It is interesting to note from the profile on Petrea volubilis published on ZipcodeZoo.com which mentioned the innovative uses of the elliptical leaves of this plant as a substitute for sandpaper for small handycraft work and emery board for filing finger or toe nails! They are also used by men who shave the hair off their head as an aid to provide a shiny look!