One magnificent tree in bloom right now in the Chiang Mai gardens and roadsides is the purple bauhinia (Bauhinia purpurea, Fabaceae).
Tem Smitinand lists it as exotic, Simon Gardner who wrote the ‘Field guide to forest trees of northern Thailand’ claims it originates in South America, while Flora of China claims it is native from Nepal to Southeast Asia and so does Kirsten Llamas. Kai and Supee Larsen who wrote the Flora of Thailand article on Bauhinia together with Jules Vidal claim it is paleotropical (a phytogeographical term for tropical Africa and Asia). I have never seen it in the jungles here in northern Thailand so like Smitinand and Gardner I do not think the purple bauhinia is native. Where is its origin?
It was scientifically described by Swedish physician and botanist Carl Linnaeus in 1753 in Species Plantarum vol. 1:375. He claimed the ‘habitat’ is “Indiae arenosis” and he cited Hendrik van Rheede, Governor of Dutch Malabar in 1670-1677. Rheede’s magnum opus ‘Hortus Malabaricus‘ was published in twelve volumes in 1678-1703. It treats 742 plant species from Kerala, India, selected due to their medicinal and economical importance. Many seemingly Indian plants were introduced long before Rheede, such as tamarind (Tamarindus indica) which is native to East Africa. However, had purple bauhinia been native to other parts of the world then Linnaeus would have known it from there too, since many students and colleagues would have sent him samples or reports. No such observation was cited in this or later editions of Species Plantarum. Since purple bauhinia was reported from India in the 17th century (but not from Africa nor South America) then I believe it is a native there, and probably native to other parts of tropical Asia too, but hardly to Chiang Mai due to its absence in the native forests.
A 17th century botanist.
The Thais call the purple bauhinia ‘siao dok dhaeng’, while ‘siao dok khao’ refers to another species: Cherry bauhinia (Bauhinia variegata). This is indeed native to Chiang Mai; fast growing, gorgeous white flowers and unlike purple bauhinia it blooms on naked branches – an awesome sight in January-February! Confusingly, as a result of man’s garden selections and love for aberrations there are red and white forms of both species. How can you tell them apart? Purple bauhinia has only three stamens even when white, and cherry bauhinia has five stamens even when red. What if you encounter one of the common crosses? The hybrid has ridged buds like in purple bauhinia (see picture above) but five stamens like in cherry bauhinia.
For the Chiang Mai home gardener the good news is that both bauhinias are easy to grow. Purple bauhinia seem more water demanding which is not surprising considering its wetter home in Kerala. This may explain its failure to establish itself in the Chiang Mai jungles. Cherry bauhinia can be left alone without water for half a year. Both species can be transplanted even as large trees. Normally I discourage people from buying large trees but in this case I say go ahead. I have tried it myself.
Text & Photo: Eric Danell
Copper engraving: Hortus Malabaricus volume 1.