Tumid nectary of S.tetraptera differences from others.Nectary of S.erythrosticta remains with nectaria caduca,but nectaries of S.franchetiana and S.tetraptera remain with nectaria persistentia.

• 红直獐牙菜为脱落蜜腺，而抱茎獐牙菜和四数獐牙菜为宿存蜜腺。