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A Thai willow

December 26, 2012

This time of the year you do not see many native trees in blossom along the Chiang Mai roads. One extraordinary exception is the Thai willow (Salix tetrasperma, Salicaceae).

Salix tetrasperma.Dec.24.2012.72When the tree blooms at Christmas time it looks greenish-yellow from a distance, but when you walk up to the tree it turns more whitish-green.

Salix tetrasperma male.72These are the flowers of a male Thai willow tree.

Salix tetrasperma.ricefieldA Chiang Mai rice field scenery with a Thai willow in the centre. To see this tree in reality, drive along the Chiang Mai canal road and make a stop at the sandy flat area just north of the Hang Dong golf club. With good shoes you can walk between the rice fields. There are good sightings 500 m north of the Ton Kwain intersection too, but it is hard to walk up to those trees. The tree is called ‘kai non’ by the nearby farmers, but Smitinand writes ‘khrai nun’.

Salix tetrasperma.bee.72Like in early springtime in Sweden, the willow is crowded with hungry wild bees and flies.

Salix tetrasperma.bark.72The bark is striated and similar to the European willows.

To me it is most surprising that this enchanting tree, suitable for erosion control along streams and a lovely ornamental near your pond, is so difficult to find in a nursery. We had a small specimen at Dokmai Garden but we managed to kill it when we moved it to another area. Yesterday I took new woody cuttings which I liberated from leaves and flowers and planted in a sandy and moist pot.

A strange phenomenon is that the Thai willow makes flowers and seeds in the cold and dry season when there are hardly any other wild flowers (November-January) and it becomes dormant and sheds leaves in the late rainy season when most other native plants grow at maximum speed.

Its ability to grow in wet (flooded) habitats enables pollination at a time when there is not much competition from other plant species, and seed dispersal via the wind while it is still dry. In the dry season there are more muddy surfaces available for seed germination than in the rainy season when it is flooded. The dormancy in the rainy season may terrify a gardener who thinks the tree is dead, but might be an adaptation to flooding, i.e. shutting down the metabolism to lower the oxygen consumption and avoid cell death due to drowning. However, I am not aware of other willows doing this so I do find this species quite exceptional.

The tree was scientifically described and named by the Scottish director of the Calcutta Botanic Garden William Roxburgh in the book ‘Plants of the Coast of Coromandel’. Here is a link to his English text and here is a link to the illustration, both from 1795.

Text & Photo: Eric Danell

One Comment leave one →
  1. December 26, 2012 9:09 AM

    In Australia we hate weedy exotic willows, but here I agree they are a delight. As for propagation have found best results by pricking out young seedlings from sandy creek beds prior to the rains. The problem now is that most of our streams have been chnnelized to enrich the construction and political sectors of society.

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