Cassia fistula, commonly known as Golden Shower Tree or Ratchaphruek in Thai, is a flowering tree belonging to the Fabaceae family. It is native to Southeast Asia, ranging from southern Pakistan to India, Sri Lanka, Myanmar, and Thailand. Additionally, Ratchaphruek is the national flower and tree of Thailand and also the state flower of Kerala, India.

Characteristics: Ratchaphruek is a medium-sized perennial tree, reaching heights of 10–20 meters. Its flowers form long clusters measuring 20–40 centimeters, with each flower having a central axis of 4–7 centimeters. The flowers have yellow petals of equal size, and the fruit is elongated, measuring 30–62 centimeters in length and 1.5–2.5 centimeters in width. The fruit emits a strong odor and contains many toxic seeds.

The name of Ratchaphruek varies across regions. It is commonly referred to as "Koon" in Thailand, although it is sometimes mistakenly written as "Khoon." In northern Thailand, it is called "Lom Laeng," while in the south, it is known as "Ratchaphruek." Other regional names include "Lak Klua" or "Lak Khoei" among the Karen people, and "Kuphayo" among the Mon people. Due to its blooming during the Songkran Festival, it is also known as "Songkran Flower."

Cultivation: In the early stages, Ratchaphruek trees grow slowly, taking approximately 1–3 years to establish. Afterward, they grow rapidly, characterized by smooth brown bark, long yellow taproots, and numerous lateral roots. The trees typically begin flowering and fruiting when they are 4–5 years old.

Benefits and Uses: Apart from its ornamental value, Ratchaphruek also possesses medicinal properties. Extracts from its pods with ethanol can inhibit the growth of mustard greens. In Thai folklore, Ratchaphruek is considered a auspicious tree, often used in important ceremonies such as housewarming rituals and military flag ceremonies. It is believed that planting Ratchaphruek trees around one's residence brings prosperity and dignity. Additionally, its leaves are considered sacred and are used in certain rituals to recite Buddhist scriptures for auspicious purposes. Cultivated as an ornamental tree to enhance beauty and provide shade. Utilized in construction as pillars, beams, and rafters. Used in city pillar foundation ceremonies. Wood is used for furniture and has medicinal properties as a traditional remedy. Bark extract is used as a component in leather tanning (tannin). Utilized for protein precipitation. Flowers are used to reduce fever and as a vermifuge to expel intestinal worms. Seed pulp alleviates constipation and expels mucus. Seeds are extracted for viscous resin, used as an ingredient in pharmaceutical glue.

Ratchaphruek holds significant cultural and symbolic importance in Thailand and is widely revered as a sacred tree.