At the amphoeyim website I found a document which presents the three national symbols of Thailand. While I knew about the national flower before, I wasn't aware that it also has an official national animal and an architectural item. I even found an announcement in the Royal Gazette dated from 2001, making these three symbols official.
National animal is the Asian elephant (Elephas maximus), named ช้างไทย (chang thai) or Thai elephant in the announcement. The elephant is strongly interwoven in Thai tradition and history. Especially the white elephant depicted in the emblem is a symbol of the royalty, present on the flag of country till 1917. As being a majestic animal, it was even used as war elephants in the past. My photo shows elephants being bathed in an elephant farm near Chiang Mai.
National flower is the Ratchapruek (ราชพฤกษ์), Cassia fistula L. known as the Golden Shower Tree in the west. One can find this tree very often in Thailand since its yellow flowers make it very ornamental. My photo was taken at the Vin de Ray winery, but actually such a view can be found anywhere in Thailand. The rationale for choosing this plant is that it is native to Thailand, can be grown in all regions, parts of the plant are used in the traditional Thai medicine, and the wood is also good material to build houses. For example, Ratchapruek wood has been used for city pillars, foundation posts of palaces and well as flag posts.
National architectural item is the pavilion, the Thai Sala (ศาลาไทย). It is chosen since it is unique to Thailand and has a very elegant architecture. The photo shows a Sala within Don Wai temple - I noticed that in my photo stock I have no photo of a Sala for plain people sitting in the shadow, only the much more decorated ones within temples. In the emblem for this symbol, the Sala is placed on a green floor to represent the richness of the country and its agriculture. The light blue sky in the emblem represents the location of Thailand in the tropics and the happy freshness of the climate.