Kailarsenia lineata
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According to the Top Tropicals website, this plant is likely a horticultural form of Kailarsenia lineata. It is sometimes referred to as Gardenia (Kailarsenia) vietnamensis or Vietnamese Gardenia. However, the name Gardenia (Kailarsenia) vietnamensis is not recognized as a valid species taxonomically, as it does not appear on the Plants of the World Online website. On NParks' Flora & Fauna Web, this plant is identified as Gardenia jasminoides var. jasminoides.