地钱纲（Marchantiopsida）是苔藓植物中唯一一类配子体具有气孔和气室分化的类群，也称“复杂叶状体苔类”，多数种类以短命的生活史适应快速变化的环境。地钱纲目前约有20科、36属、364种，是苔藓植物中特有种和濒危种最丰富的类群，也是中国苔藓志遗留的最困难类群，在世界绝大多数地区也仍然缺乏对其物种多样性的确切了解。我国是地钱纲植物的分布中心之一，目前记载的有14科22属83种，但有近1/4的种为我国特有。但由于分类的困难、难以琢磨的生长季节以及缺乏专门的调查，我国拥有的确切物种数量难以估计。本项目拟以经典分类、分子系统学和生物地理相结合的研究方法，通过广泛而深入的野外调查、对核和叶绿体相关基因的测序以及祖先性状重建和形态特征分析，完善世界地钱纲植物的分类系统，揭示我国地钱纲植物确切的物种数量和濒危状况，探讨分布格局和成因，为苔藓植物多样性的保护和利用提供新的科学依据。

Marchantiopsida, i.e. complex thalloid liverworts, is a unique group with air pores and air chambers of the gametophytes in bryophytes. Most species in the group have a very short life cycle for an adaptation in a quick changing environment. At present Marchantiopsida contains about 364 species in 36 genera of 20 families，it has the richest endemic taxa and endangered taxa of bryophytes. It is the taxonomically most difficult group in unpublished Bryoflora of China, and it has also been still poorly known in most areas in the world. China is one of its diversity distribution centers with 83 species in 22 genera of 14 families, but about 1/4 species locally endemic. Owing to the difficult taxonomy, elusive growing seasons and the lack of special investigation, the exact number of species of this group seems to be inestimable. By the combined methods of morphological taxonomy, molecular systematics and biogeography we will carry out an intensive revision of Chinese Marchantiopsida, establish a more natural classification system, revise the taxonomic circumscriptions, reveal the exact species number of China and endangered status, and explore distribution patterns and their origins by intensive field collections, sequences of nucleus and chloroplast genes, and ancestral state reconstructions and character analyses. The project will provide the scientific evidence for the conservation and uses of bryophyte diversity.