Plants exhibiting the water-conserving crassulacean acid metabolism (CAM) photosynthetic pathway provide some of the most intriguing examples of photosynthetic diversity and plasticity. Here, a largely unnoticed facet of CAM-plant photosynthesis is highlighted: the co-occurrence of ontogenetically controlled constitutive and environmentally controlled facultative CAM in a species. Both forms of CAM are displayed in leaves of Coleus amboinicus Lour. (Lamiaceae), a semi-succulent perennial plant with oregano-like flavour that is native to southern and eastern Africa and naturalised elsewhere in the tropics. Under well-watered conditions, leaves assimilate CO₂ predominantly by the C₃ pathway. They also display low levels of CO₂ uptake at night accompanied by small nocturnal increases in leaf tissue acidity. This indicates the presence of weakly expressed constitutive CAM. CAM expression is strongly enhanced in response to drought stress. The drought-enhanced component of CAM is reversible upon rewatering and thus considered to be facultative. In contrast to C. amboinicus, the thin-leaved closely related Coleus scutellarioides (L.) Benth. exhibits net CO₂ fixation solely in the light via the C₃ pathway, both under well-watered and drought conditions. However, low levels of nocturnal acidification detected in leaves and stems indicate that the CAM cycle is present. The highly speciose mint family, which contains few known CAM-exhibiting species and is composed predominantly of C₃ species, appears to be an excellent group of plants for studying the evolutionary origins of CAM and for determining the position of facultative CAM along the C₃–full CAM trajectory.

表现出节水的克拉苏糖酸代谢（CAM）光合作用途径的植物提供了一些最有趣的光合作用多样性和可塑性的例子。在此，突出了CAM植物光合作用的一个基本未被关注的方面：一个物种中自体控制的本构性和环境控制的兼性CAM的同时存在。两种形式的CAM均显示在蓝叶锦鸡儿的叶子中。（唇形科），一种半肉质多年生植物，具有牛至风味，原产于非洲南部和东部，并在热带的其他地方自然化。在水分充足的条件下，叶子主要通过C ₃途径吸收CO ₂。它们还显示出低水平的CO ₂夜间摄取，伴有夜间夜间叶片组织酸度增加。这表明存在弱表达的组成型CAM。响应干旱胁迫，CAM表达大大增强。CAM的干旱增强成分在补水后是可逆的，因此被认为是兼性的。与C. amboinicus相比，薄叶紧密相关的Coleus scutellarioides（L.）Benth。仅在通过C ₃的光线下展示净CO ₂固定在干旱和干旱条件下的路径。但是，在叶片和茎中检测到的夜间酸化水平较低，表明存在CAM循环。高度特异的薄荷家族，几乎不包含已知的CAM展示物种，主要由C ₃物种组成，似乎是研究CAM进化起源和确定兼性CAM沿C ₃位置的优秀植物。–完整的CAM轨迹。