依据红树植物在潮间带的分布，将其分为真红树植物和半红树植物两大类。但对一些过渡地带种类的归属问题一直存在争议。该研究选取国内大部分红树植物，比较其成熟叶片中的Cl含量、肉质化程度、比叶面积（SLA）、单位重量叶氮含量（Nmass）和单位面积叶氮含量（Narea），并对争议树种重新进行界定。结果表明：1）真红树植物叶片中Cl含量和肉质化程度远高于半红树植物；2）真红树植物具有低SLA和高Narea的特点，除水芫花(Pemphis acidula)外半红树植物具有高SLA和低Narea的特点。3）争议的7种红树植物中，银叶树（Heritiera littoralis）、海漆（Excoecaria agallocha）、卤蕨（Acrostichum aureum ）和尖叶卤蕨（Acrostichum speciosum）归为半红树植物更合适；老鼠（Acanthus ilicifolius）和小花老鼠（Acanthus ebrecteatus）归为真红树植物。木果楝（Xylocarpus granatum）有待进一步研究。
Aims Mangrove plants are usually categorized as true mangrove plants and semi-mangrove plants on the basis of their distribution in inter-tidal regions. However, the identification of some fringe mangrove species found mainly on the landward transitional zones is controversial. Specific leaf area (SLA, leaf area per unit dry mass) and mass- and area-based leaf nitrogen concentrations (Nmass and Narea) are important leaf traits for plants, but relevant comparative research on true and semi-mangrove plants is unavailable. Our objective was to determine differences between the two groups and to classify the controversial species according to their leaf traits. Ultimately, this will assist in the management, protection and utilization of mangrove forest.
Methods Three individuals in similar growth sites were chosen for each species from Hainan Island. Fully expanded mature leaves were sampled from the upper canopy of all plants. Succulence (water content per unit leaf area), SLA, Nmass and Narea of mature leaves were studied for 33 species, representing all but three of the mangrove species in China.
Important findings True mangrove plants accumulated more Cl and water per unit leaf area than semi-mangrove plants, except for Pemphis acidula, Hernandia sonora and Clerodendrum inerme. Cl and water content per unit leaf area of true mangrove plants were generally >2.5 mg·cm－2 and >2.4 g·dm－2, respectively. Cl concentrations were positively related to succulence for all mangrove species. True mangrove plants had low SLA (<100 cm2·g－1) and high Narea; however, semi-mangrove plants had high SLA (mean of 160.4 cm2·g-1). Pemphis acidula had much lower SLA than other semi-mangrove species. Our study suggested that there are significant differences between true mangrove plants and semi-mangrove plants in leaf Cl concentration, succulence, SLA, Nmass and Narea. Heritiera littoralis, Excoecaria agallocha, Acrostichum aureum and Acrostichum speciosum are better classified as semi-mangrove plants, while Acanthus ilicifolius and Acanthus ebrecteatus are classified as true mangrove plants, and Xylocarpus granatum needs further research.