Calotropis gigantea - The Giant Milkweed

You know what people say, to relax you need to stop and smell the roses. So on a recent trip to Vientiane, I did just that, except that the flower I was trying to smell wasn't a rose, and had no scent. Nevertheless, this lovely shrub that I noticed whilst walking around Vientiane, Laos is Calotropis gigantea, also known as Giant milkweed or Crown flower.

This plant is a weed and a member of the subfamily Asclepiadoideae of the Apocynaceae family. Asclepiadoideae (formerly Asclepiadaceae family), that contains plants that many of us are familiar with including milkweeds (Asclepias), Hoyas, Dischidias and succulents like the carrion or toad plant (Stapelia).

Calotropis gigantea or the Giant Milkweed. This plant was growing on a patch of soil by the road in Vientiane, Laos.

Calotropis gigantea can be found in exposed wastelands of India through to Indochina, southwards to Northern Australia and northwards to Southern China. The plants have sessile, alternate, gray-green rounded-ovate leaves and whitish stems that can grow up to 4 metres high. The plant is rather robust and branching occurs all over, including from just above the ground level.

White form of the Giant Milkweed - this was growing along the path on the park facing the Mekong River in Vientiane, Laos.

Breaking any part of the stem or leaves results in copious milky sap oozing from the wounds. The sap and the entire plant contain several toxic cardenolides. The sap also has uscharin and other unknown vesicant irritant, and coming in contact with the sap can result in skin or mucosal irritation.

The blusih flower is very striking against the gray-green leaves.

However, parts of this plant are used in Ayurvedic medicine, by itself or in combination with other herbs as treatment for various ailments. The plant also has religious significance to the Indian community, and here in Malaysia, is commonly planted for that purpose.

White buds of the white flower form of Caltropis gigantea.

The flowers come in white or tinted with a bluish-purple hue, and double petal forms exist in the nursery trade, particularly in Thailand. The flowers have gynostegium, a structure formed by the fusion of stigma and the androecium. Pollen of this flower are grouped into pollinia, and are attached to a glandular, adhesive disc that sticks to the feet of visiting bees.

The bladder-shaped fruit of Calotropis gigantea.

The fruit is an oddly shaped bladder-like pod that splits open when ripe, releasing lightweight brow seeds with a tuff of white hair attached at one end that allows wind dispersal of seeds.

The ripe fruit/pod splits, and reveals brown seeds with tuff of hairs that get carried away by the breeze.

The plants that I find on the streets and on grassy openings in Vientiane appear to be wild and both the bluish-tinged and white flower forms can be found there.