Strongylodon macrobotrys A.Gray (Fabaceae)


Jade vine

Flowers of Strongylodon macrobotrys in Oxford Botanic Garden. Leaves of Strongylodon macrobotrys in Oxford Botanic Garden.

The jade vine is endemic to the rainforests on the Philippine islands of Luzon, Mindoro and Catanduanes. The pendulous, floral tresses, up to 3 m long, containing many hundreds of thumb-length, translucent, blue-green flowers, make the jade vine a spectacular glasshouse ornamental. The species name, macrobotrys. The species name, macrobotrys, refers to these large clusters of flowers.

When not in flower, the woody stems, up to 20 m long, covered in large, tough, dark-green trifoliate leaves hardly seem to merit attention. Despite its size and distinctive appearance, the vine is related to humbler looking, and more familiar, plants, such as runner beans and soya beans.

The jade vine is thought to be bat pollinated. At dusk, bats appear attracted by the luminosity of the flowers. Hanging upside down from the floral tresses, bats force their faces into each claw-like flower to get at the copious, sweet, sticky nectar. In the process, their heads are dusted with pollen that they then transfer to the stigmas of other flowers. Other members of this small genus, which are distributed from Hawai'i west across the Pacific Ocean to southeast Asia and Madagascar, are also mammal pollinated, e.g., the yellow-flowered, lemur-pollinated, Malagasy endemic Strongylodon craveniae.

The distinctive colour of the jade vine flower is due to the co-occurrence of two pigments, an anthocyanin (malvin) and a flavone (saponarin), in the epidermal cells of the petals. The sap inside these cells is slightly alkaline, turning malvin blue and saponarin yellow, which produces turquoise.

The horticultural potential of the jade vine, formally described in 1854, was not recognised until the 1930s. By the 1960s, the vine was being grown in large gardens and collections outside of the Philippines. However, jade vines rarely produce their large, indehiscent, fleshy, few-seeded pods in cultivation. The reason appears to be that Strongylodon macrobotrys is self-incompatible, i.e., it rarely mates with itself. Jade vine seeds are shorted lived, which combined with the few introductions from the wild into cultivation, means cultivated individuals are likely to be closely related to each other. Furthermore, most cultivated plants are produced by clonal propagation and few glasshouses are large enough to house more than one individual plant.

With limited genetic variation in cultivation and seed that are difficult to store, options for ex situ conservation of the jade vine are limited. However, in situ conservation is also difficult as threats, such as habitat destruction, continue across the species' native range.

Further reading

Polhill, RM 1972. Strongylodon macrobotrys (Leguminosae). Curtis's Botanical Magazine 174: t.627.

Prychid CJ et al. 1998. Fruit and seed set in Strongylodon macrobotrys. In: Owens SJ & Rudall PJ (eds) Reproductive biology: in systematics, conservation and economic botany. Royal Botanic Gardens, Kew, 345-352.

Takeda K et al. 2010. Greenish blue flower colour of Strongylodon macrobotrys. Biochemical Systematics and Ecology 38: 630-633.

Stephen Harris