Hoya siamica is a slender vine found in Thailand with long light green leaves. The leaves are on average 1.5–2 cm wide by 4–10 cm long. It has white flowers that come in clusters of 10 to 15. The corolla of the flowers are white and flat; the corona can be a deep purple or a very pale yellow depending on how much light the plant receives. The flowers are approximately 1.5 cm in diameter, fuzzy, have a slight scent, and last about a week when they flower during the summer.