以大花组的束花石斛（Dendrobium chrysanthum）和黄花石斛（D. dixanthum）为材料，对它们的光合生理等进行了系统研究.2种石斛叶片的解剖结构为异面叶，气孔仅分布在下表面，具气孔盖，叶脉维管束鞘不含叶绿体，无花环型结.2种石斛的光强、CO2浓度和温度的响应研究表明，它们的光补偿点（LCP）和光饱和点（LSP）分别为5～10μmol/(m2?s) 和850～900μmol/(m2?s),最大光合速率（Pn）在～6μmol/(m2?s)；CO2补偿点和饱和点分别为80～90 μmol/mol和800 μmol/mol；光合作用的最适温度在26～30℃.2种石斛兰的Pn日变化为双峰型曲线，首峰出现在12:00左右，最大光合速率在5～6μmol/(m2?s)，次峰出现在15:00左右，夜间不吸收CO2.2种石斛的PEPCase活性极低，具有较高的RuBPCase和GO酶活性.以上的研究结果表明，束花石斛和黄花石斛光合作用碳同化途径属C3植物类型，具有半阴生植物的特点.
Photosynthetic physiology of Dendrobium williamsonii and D. longicornu were studied. Cross-sections of the leaves of 2 Dendrobium species showed that they were bifacial leaves. The abaxial epidermis had large amount of stomata, which covered by the waxy stomatal cover, the vascular bundles had no chloroplast and no ‘Kranz’ structures. Their light compensation points (LCP) were 5-10 μmol?m?2?s?1, the light saturation points (LSP) were ranged from 850 to 900 μmol?m?2?s?1, max photosynthetic rate was around 6 μmol CO2?m?2?s?1; the CO2 compensation points (CCP) and the saturation points (CSP) were 80-90 μmol?mol?1 and 800 μmol?mol?1, respectively, the optimum temperatures of the photosynthesis were in range of 26-30°C. The Pn diurnal variations of 2 Dendrobium species were all bimodal curves, with the first peaks ca 5-6 μ mol CO2 m?2 s?1 and emerging at between 11:00-12:00, and the second peaks emerging at about 15:00, and no CO2 absorption occurred in night. 2 Dendrobium species both had relatively high RuBPCase and GO activities, but very low PEPCase activities. All results suggested that Dendrobium chrysanthum and D. dixanthum were typical semi-shade C3 plants.