樟科油丹属复合群的系统学研究

Evolution of living beings has given rise to diversified clades on the planet. Plant systematics/taxonomy is to recognize and describe such monophyletic clades of plants. A taxon (e.g. a family, or a genus, or a species) should be a monophyletic clade. Generic delimitation within Lauraceae has been controversial, many genera in the family are not monophyletic. Phylogeny based on DNA sequencing provides a powerful tool to resolve the problem. Alseodaphne together with Nothaphoebe and Dehaasia constitute a taxonomic complex (the Alseodaphne complex) in the family Lauraceae. The three genera include over 135 species that are endemic to Tropical Asia. The Alseodaphne complex is polyphyletic according to recent phylogenetic studies. Many molecular systematic studies on Lauraceae were published, but the Alseodaphne complex remains poorly understood because (1) sampling is poor: only 11 of 135 known species were sampled in phylogenies, so that it remains unclear how many clades this complex includes; (2) relationships of some small clades were poorly resolved due to low resolution of molecular markers and polytomy in the published phylogenies; (3) there is no consensus about how to define these clades using morphological characters. Consequently, a new taxonomic revision is urgently needed based on reasonable sampling and well resolved phylogenetic studies. This aim can be reached by the following strategy. (1) Sampling is crucial to a new phylogenetic study of the complex. As it will be impossible to get materials of all known species, we plan to conduct an analysis of morphological clusters, e.g. anther 2-celled vs. 4 celled, fruit pedicels swollen vs. not swollen, tepals unequal vs. equal, tepals persistent vs. deciduous, and sample 3 or more species for each morphological cluster. In total, we plan to sample 30-50 species from Tropical Asia, China, Indonesia, and Malaysia in particular. (2) To resolve relationships of those small clades, we plan to analyze multiple fragments including both nrDNA (ITS and LEAFY intron II) and chloroplast genes (e.g. psbA-trnH, rpl16, trnL-F, and matK) for a better resolved phylogenetic tree. (3) Leaf cuticle anatomy is an important source of taxonomic characters in Lauraceae. We plan to investigate leaf cuticle variation patterns and understand their taxonomic utility for the Alseodaphne complex. (4) Morphology is the soul of systematics. It is important to find apomorphic morphological characters to define the clades in a new phylogenetic tree. Therefore, we plan to comb through macromorphological characters based on literature records, herbarium specimens, and field observations. (5) Based on this integrative study, we plan to arrive at a new taxonomic treatment of the Alseodaphne complex. We expect to publish 8 papers in internationally recognized journals. Our new taxonomy is fundamental to floristic, ecological, and palaeoclimatic studies of Tropical Asia.

现代植物系统学要求分类要基于系统发育，分类群为单系群。樟科油丹属与其近缘的赛楠属和莲桂属构成一个多系的复合群，分布于热带亚洲，从中国南部至新几内亚。在进一步取样和系统发育研究基础上，对该复合群开展分类修订工作势在必行。目前对该复合群研究存在的问题在于：（1）取样不足，复合群约135种，但取样仅11种，代表性严重不足；（2）由于取样不足，复合群包含多少分支还不清楚；（3）系统发育研究所用分子标记的分辨率不足，部分分支与近缘分支的关系还需进一步研究确定。本项目拟开展如下工作：（1）分析重要分类特征，选取代表种类并开展野外观察和取样，特别是对重要分布区印度尼西亚开展采集；（2）选取多个片段开展系统发育重建，搞清该复合群的所有分支，以及分支与鳄梨族其他近缘群的关系；（3）开展叶表皮结构解剖研究；（4）梳理宏观形态学特征；（5）搞清各分支的定义特征；（6）对油丹属复合群做新的分类学处理。

樟科植物不仅是热带森林植被的重要组成，而且还有重要的经济利用价值，但是分类基础薄弱，这种状况限制了该科植物的生物多样性保育以及资源利用等方面的研究。油丹属复合群包括油丹属、赛楠属和莲桂属，其属的界定历来有争议。近年来的分子系统学研究表明，该复合群是多系。本项目的主要目标就是在系统发育研究基础上，开展分类学研究，理清油丹属复合群的属的界定。我们在野外调查和采样基础上，重点开展了三个方面的研究工作。基于nrITS和单拷贝核基因LEAFY开展了油丹属复合群的分子系统学研究，发现该复合群包含三个主要分支：第一个分支包含赛楠属、莲桂属和油丹属的模式种以及黄连山油丹，第二支主要包含产自云南的大多数油丹属种类，第三支包含海南产油丹属种类和云南油丹。第二支和第三支构成一个大分支的支持率较低（BS: 64, PP: 0.67），这个无模式种的大分支已经被描述为北油丹属Alseodaphnopsis H.W. Li & J. Li。我们对包括营养器官和生殖器官的特征变异式样进行了观察和研究，发现该复合群包含三个主要亚群：1）亚群I，果实椭圆形，果柄肉质有疣或木质锈色有纵棱；2）亚群II，果实球形或扁球形，果柄柱状；3）亚群III，果实不规则椭圆形，常偏斜，果柄微膨大，这些特征对应于系统发育研究发现的三个分支，可以作为分支的定义特征。在系统发育和形态学研究的基础上，结合模式标本考证，我们重新界定了油丹属复合群的属，并对所属种类进行组合等分类学处理，发现新属2个，新种2个，新组合75个，新名称3个。本项目基本上搞清了油丹属复合群的分类问题，为樟科植物的物种编目、生物多样性保护等奠定了重要的基础。在该项目的资助发表12篇SCI论文，4篇核心期刊和4部论著。