Hong Kong Orchid Tree
|Bauhinia × blakeana|
|Bauhinia × blakeana flower|
B. × blakeana
|Bauhinia × blakeana|
Bauhinia × blakeana, commonly called the Hong Kong Orchid Tree, is a legume tree of the genus Bauhinia, with large thick leaves and striking purplish red flowers. The fragrant, orchid-like flowers are usually 10 to 15 centimetres (3.9 to 5.9 in) across, and bloom from early November to the end of March. Although now cultivated in many areas, it originated in Hong Kong in 1880 and apparently all of the cultivated trees derive from one cultivated at the Hong Kong Botanical Gardens and widely planted in Hong Kong starting in 1914. It is referred to as bauhinia in non-scientific literature though this is the name of the genus. It is sometimes called the Hong Kong orchid (香港蘭). In Hong Kong, it is most commonly referred to by its Chinese name of "洋紫荊". Also see "Kanchan Flower"(Bengali) for reference.
The Bauhinia double-lobed leaf is similar in shape to a heart or a butterfly. A typical leaf is 7 to 10 centimetres (2.8 to 3.9 in) long and 10 to 13 centimetres (3.9 to 5.1 in) wide, with a deep cleft dividing the apex. In Hong Kong the leaf is known as the "clever leaf" (聰明葉), and is regarded as a symbol of wisdom. Some people use the leaves to make bookmarks in the hope that they will bring them good luck in their studies.
It is sterile, which means it does not generally produce seeds or fruits, and is a hybrid between Bauhinia variegata and Bauhinia purpurea. The 2008 research was able to identify the female parent as Bauhinia purpurea, but it could not differentiate the male parent from Bauhinia variegata var. variegata or Bauhinia variegata var. candida. This is not unexpected, as Bauhinia variegata var. candida is a white-flowered form of Bauhinia variegata var. variegata, and not a separate species or sub-species. The 2005 research suggested Bauhinia × blakeana is genetically closer to Bauhinia variegata, while the 2008 research indicated it is closer to Bauhinia purpurea instead.
Propagation is by grafting, cuttings and air-layering. As it is only known in cultivation, it can also be named as a cultivar: Bauhinia 'Blakeana'. Hong Kong orchid trees are usually sterile, yet here, too, there are exceptions. One tree has been found in Hong Kong that produces seeds, perhaps indicating that evolution or mutation has occurred, or that even though Bauhinia × blakeana is perhaps sterile when self-pollinated (the scientific study in 2005 established the low fertility of Bauhinia × blakeana's pollen when compared with its parental species Bauhinia purpurea or Bauhinia variegata), however, it may perhaps be able to produce seeds when pollinated instead by its parental species Bauhinia purpurea or Bauhinia variegata or other related Bauhinia species. More scientific research will need to be carried out, e.g., artificial controlled cross-pollination experiments to confirm the ability of Bauhinia × blakeana in backcross or outcross to produce (fertile) seeds.
Lawrence Ramsden of the University of Hong Kong's Department of Botany is conducting the search to find out if there are any more individuals that can produce seeds – if so, they could benefit propagation of the tree for horticulture. Two previous instances of seeds found from Bauhinia × blakeana specimens failed to germinate. Development of seed pods (but no seeds) from B blakeana (see footnote 5 link with photos) have been observed on three trees in Tai Po and Kowloon in Hong Kong. These three B blakeana trees with numerous seed pods were grown alongside B purpurea, B variegata candida (white flower) and B variegata. At the time (March in Hong Kong), both B blakeana and B purpurea were flowering, therefore, the pollens for development of B blakeana seed pods may have been contributed from B purpurea.