樟科琼楠亚族的分类学

The Lauraceae are economically important as sources of medicine (e.g. Cinnamomum cassia and Lindera aggregata), timber (e.g., Phoebe spp.), nutritious fruits (e.g., Persea americana), spices (e.g., Cinnamomum cassia, C. subavenium, Laurus nobilis), camphor and essential oil of C. camphora used for making perfumes and medicines. However, many species remain poorly known and difficult to identify, some are even equivocal for their generic ascription. Modern plant taxonomy is based on phylogeny and monophyly is an essential prerequisite. The subtribe Beilschmiediineae Kosterm. belongs to the Tribe Cryptocaryeae of the Lauraceae, the subtribe is monophyletic and widely distributed in the pantropical region, it contains seven genera including Beilschmiedia, Endiandra, Syndiclis, Sinopora, Potameia, Hexapora, and Yasunia. Previous studies have suggested that a few genera in the subtribe are not monophyletic, and generic delimitation and relationships among the genera are ambiguous. The existing problems are: (1) due to inadequate sampling and low resolution of molecular markers in previous studies, it remains unclear how many generic clades are there in the subtribe? The subtribe has ca. 390 species in the world, 64 species were sampled in a recently published phylogeny, sampling from the Asia is extremely poor in the latest phylogeny; (2) it is unclear how to define the generic clades using morphological characters? (3) phylogenetic relationships among the known clades are poorly resolved based on ITS or trnK alone or combined. To tackle these taxonomic problems, we plan to: (1) catalog species of the subtribe based on field collections, herbarium specimens, and literature data, investigate morphological characters, which lay foundations for reasonable sampling, phylogeny and defining clades; (2) sample more Asian species, obtain more useful sequences, e.g. the low-copy nuclear LEAFY and RPB2, and the chloroplast psbA-trnH, rpl16, and trnL-F, then conduct molecular systematic studies to establish a backbone for a species-rich phylogeny; (3) reconstruct a phylogenetic tree based on a combined dataset including morphological and molecular data, delimit the generic clades and resolve phylogenetic relationships of the generic clades; (4) analyze morphological characters using Mesquite to define generic clades using morphological characters based on a new character analysis; (5) accomplish a new taxonomic treatment according to the latest nomenclatural code (will be the Shenzhen Code after 2017). The subtribe is speciose, and contains many economically important species and endangered species with confined distribution. A new taxonomy of the subtribe is of great significance in a world species catalogue of Lauraceae, resource utilization of species, and conservation of endangered species.

琼楠亚族隶属樟科厚壳桂族，是一个单系分支，泛热带分布，包含琼楠属、土楠属、油果樟属、孔药楠属、Potameia、Hexapora和Yasunia等7属。琼楠亚族内的属间关系混乱，主要问题包括：（1）该亚族内包含多少个属级分支？（2）如何用形态特征来定义亚族内的属？（3）属间关系如何？本项目拟采取如下方案：（1）完成物种编目，考察和分析形态特征，为取样、系统发育和定义分支等奠定基础；（2）分子系统学研究建立系统发育骨架；（3）联合形态和分子数据建立系统发育树，界定琼楠属群包含的属级分支，并确定属间关系；（4）开展特征分析，用共衍征定义属；（5）基于植物分类学原理和命名法规进行分类处理。琼楠亚族包含种类较多，包含很多经济利用价值高和受威胁严重的物种。本项目解决琼楠亚族的分类学问题对于完成全球樟科物种编目以及琼楠亚族物种资源利用和濒危物种保育有重要意义。

樟科琼楠属群包含7属，琼楠属、土楠属、油果樟属、孔药楠属、Hexapora属、Potameia属和Yasunia属，属间关系不清楚。在项目资助下，我们主要开展了物种编目、形态学、解剖学、器官发育和系统发生等方面的研究，利用多学科证据探讨该琼楠属群的属间关系。（1）物种编目，我们完成了全球樟科的物种编目，包括琼楠属群的全部物种。（2）对樟科形态学、叶表皮解剖和花器官发育进行了深入地研究。野外调查和宏观形态学研究发现云南东南部樟科两个新种，即金平楠和河口楠。对非洲琼楠属植物的叶表皮结构研究揭示叶表皮结构特征有比较重要的分类价值，尤其是气孔器特征，与基于宏观形态特征的分组结果比较接近。对樟科樟属叶表皮结构的研究也揭示叶表皮结构特征具有重要分类价值，其叶表皮上表皮明显分为两类，一类是细胞形状比较规则，垂周壁直且平周壁无网格，另一类是细胞形状不规则，垂周壁扭曲且平周壁具网格；该结果与分子系统学研究结果吻合，支持将樟属划分为两个属。对琼楠属山潺的花器官研究表明，该种花器官各部分有高度的易变性，花基数3、4、5基数都有，腺体与第三轮雄蕊没有稳定联系，且第三轮雄蕊从完全发育、部分败育到完全败育，使得基于雄蕊数目的分类划分变得困难。（3）开展了系统发生基因组学的研究。我们基于叶绿体基因组对琼楠属群进行了系统发生重建和分子钟定年，揭示该属群包含三个主要分支，即澳洲分支（澳洲琼楠属和土楠属），非洲分支（非洲琼楠属植物与Potameia属）和亚洲——美洲分支（油果樟属、Yasunia属和亚洲-美洲琼楠属植物），琼楠属是多系群，现代泛热带分布是由于长距离扩散形成，而不是前人主张的冈瓦纳古陆分裂导致的隔离分化产生。我们还利用简化基因组结合常规标记开展了系统发生研究，包含了更多的琼楠属群样品，其结果与系统发生叶绿体基因组研究结果比较接近。