Steffen Simone, Ball Peter, Mucina Ladislav, Kadereit Gudrun
Institute für Allgemeine und Spezielle Botanik, Johannes Gutenberg-Universität Mainz, Germany, Biology Department, University of Toronto at Mississauga, Mississauga, ON, L5L 1C6, Canada and School of Plant Biology, The University of Western Australia, 35 Stirling Hwy, Crawley WA 6009, Perth, Australia; Department of Geography & Environmental Studies, Stellenbosch University, Private Bag X1, Matieland 7602, Stellenbosch, South Africa.
Institute für Allgemeine und Spezielle Botanik, Johannes Gutenberg-Universität Mainz, Germany, Biology Department, University of Toronto at Mississauga, Mississauga, ON, L5L 1C6, Canada and School of Plant Biology, The University of Western Australia, 35 Stirling Hwy, Crawley WA 6009, Perth, Australia; Department of Geography & Environmental Studies, Stellenbosch University, Private Bag X1, Matieland 7602, Stellenbosch, South Africa
Ann Bot. 2015 Feb;115(3):353-68. doi: 10.1093/aob/mcu260. Epub 2015 Jan 23.
Sarcocornia comprises about 28 species of perennial succulent halophytes distributed worldwide, mainly in saline environments of warm-temperate and subtropical regions. The genus is characterized by strongly reduced leaves and flowers, which cause taxonomic difficulties; however, species in the genus show high diversity in growth form, with a mat-forming habit found in coastal salt marshes of all continents. Sarcocornia forms a monophyletic lineage with Salicornia whose species are all annual, yet the relationship between the two genera is poorly understood. This study is aimed at clarifying the phylogenetic relationship between Sarcocornia and Salicornia, interpreting biogeographical and ecological patterns in Sarcocornia, and gaining insights into putative parallel evolution of habit as an adaptation to environmental factors.
A comprehensively sampled and dated phylogeny of Sarcocornia is presented based on nuclear ribosomal DNA (external transcribed spacer) and chloroplast DNA (atpB-rbcL, rpl32-trnL) sequences; representative samples of Salicornia were also included in the analyses. To infer biogeographical patterns, an ancestral area reconstruction was conducted.
The Sarcocornia/Salicornia lineage arose during the Mid-Miocene from Eurasian ancestors and diversified into four subclades: the Salicornia clade, the American Sarcocornia clade, the Eurasian Sarcocornia clade and the South African/Australian Sarcocornia clade. Sarcocornia is supported as paraphyletic, with Salicornia nested within Sarcocornia being sister to the American/Eurasian Sarcocornia clade. The American and the South African/Australian Sarcocornia clade as well as the Salicornia clade were reconstructed to be of Eurasian origin. The prostrate, mat-forming habit arose multiple times in Sarcocornia.
Sarcocornia diversified in salt-laden environments worldwide, repeatedly evolving superficially similar prostrate, mat-forming habits that seem advantageous in stressed environments with prolonged flooding, high tidal movement and frost. Some of these prostrate-habit types might be considered as ecotypes (e.g. S. pacifica or S. pillansii) while others represent good ecospecies (e.g. S. perennis, S. decumbens, S. capensis), hence representing different stages of speciation.
盐角草属包含约28种多年生肉质盐生植物，分布于全球，主要生长在暖温带和亚热带地区的盐碱环境中。该属植物的特点是叶片和花朵极度退化，这给分类带来了困难；然而，该属植物在生长形态上具有高度多样性，在各大洲的沿海盐沼中都有形成垫状的习性。盐角草属与盐节草属构成一个单系类群，盐节草属的物种均为一年生植物，但这两个属之间的关系尚不清楚。本研究旨在阐明盐角草属与盐节草属之间的系统发育关系，解读盐角草属的生物地理和生态模式，并深入了解作为对环境因素适应的习性的假定平行进化。
基于核糖体DNA（外部转录间隔区）和叶绿体DNA（atpB-rbcL、rpl32-trnL）序列，构建了一个全面采样并确定年代的盐角草属系统发育树；分析中还纳入了盐节草属的代表性样本。为推断生物地理模式，进行了祖先分布区重建。
盐角草属/盐节草属类群在中新世中期起源于欧亚大陆祖先，并分化为四个亚分支：盐节草分支、美洲盐角草分支、欧亚盐角草分支和南非/澳大利亚盐角草分支。盐角草属被支持为并系群，嵌套在盐角草属内的盐节草属是美洲/欧亚盐角草分支的姐妹群。美洲和南非/澳大利亚盐角草分支以及盐节草分支被重建为起源于欧亚大陆。盐角草属中伏地、形成垫状的习性多次出现。
盐角草属在全球充满盐分的环境中多样化，多次进化出表面上相似的伏地、形成垫状的习性，这些习性在洪水泛滥时间长、潮汐活动频繁和有霜冻的压力环境中似乎具有优势。其中一些伏地习性类型可能被视为生态型（如太平洋盐角草或皮氏盐角草），而其他一些则代表良好的生态物种（如多年生盐角草、平卧盐角草、开普盐角草），因此代表了物种形成的不同阶段。
