Abstract：
The Hildenbrandiales, a typically saxicolous red algal order, is an early diverging florideophycean group with global significance in marine and freshwater ecosystems across diverse temperature zones. To comprehensively elucidate the diversity, phylogeny, biogeography, and evolution of this order, we conducted a thorough re-examination employing molecular data derived from nearly 700 specimens. Employing a species delimitation method, we identified Evolutionary Species Units (ESUs) within the Hildenbrandiales aiming to enhance our understanding of species diversity and generate the first time-calibrated tree and ancestral area reconstruction for this order. Mitochondrial cox1 and chloroplast rbcL markers were used to infer species boundaries, and subsequent phylogenetic reconstructions involved concatenated sequences of cox1, rbcL, and 18S rDNA. Time calibration of the resulting phylogenetic tree used a fossil record from a Triassic purportedly freshwater Hildenbrandia species and three secondary time points from the literature. Our species delimitation analysis revealed an astounding 97 distinct ESUs, quintupling the known diversity within this order. Our time-calibration analysis placed the origin of Hildenbrandiales (crown age) in the Ediacaran period, with freshwater species emerging as a monophyletic group during the later Permian to early Triassic. Phylogenetic reconstructions identified seven major clades, experiencing early diversification during the Silurian to Carboniferous period. Two major evolutionary events-colonization of freshwater habitats and obligate systemic symbiosis with a marine fungus-marked this order, leading to significant morphological alterations without a commensurate increase in species diversification. Despite the remarkable newly discovered diversity, the extant taxon diversity appears relatively constrained when viewed against an evolutionary timeline spanning over 800 million years. This limitation may stem from restricted geographic sampling or the prevalence of asexual reproduction. However, species richness estimation and rarefaction analyses suggest a substantially larger diversity yet to be uncovered-potentially four times greater. These findings drastically reshape our understanding of the deeply diverging florideophycean order Hildenbrandiales species diversity, and contribute valuable insights into this order\'s evolutionary history and ecological adaptations. Supported by phylogenetic, ecological and morphological evidence, we established the genus Riverina gen. nov. to accommodate freshwater species of Hildenbrandiales, which form a monophyletic clade in our analyses. This marks the first step toward refining the taxonomy of the Hildenbrandiales, an order demanding thorough revisions, notably with the creation of several genera to address the polyphyletic status of Hildenbrandia. However, the limited diagnostic features pose a challenge, necessitating a fresh approach to defining genera. A potential solution lies in embracing a molecular systematic perspective, which can offer precise delineations of taxonomic boundaries.
摘要：
Hildenbrandiales,一种典型的色泽红藻，是一个早期分歧的植物区系，在不同温度区的海洋和淡水生态系统中具有全球意义。为了全面阐明多样性，系统发育,生物地理学,以及这种秩序的演变，我们使用来自近700个样本的分子数据进行了彻底的重新检查。采用物种划界方法，我们确定了Hildenbrandiales中的进化物种单位（ESU），旨在增强我们对物种多样性的理解，并为该顺序生成首次时间校准的树木和祖先区域重建。线粒体cox1和叶绿体rbcL标记用于推断物种边界，随后的系统发育重建涉及cox1，rbcL，和18SrDNA。产生的系统发育树的时间校准使用了三叠纪据称淡水Hildenbrandia物种的化石记录和文献中的三个次要时间点。我们的物种定界分析揭示了惊人的97个不同的ESU，在这个顺序中将已知的多样性增加了五倍。我们的时间校准分析将Hildenbrandiales（冠龄）的起源置于Ediacaran时期，在二叠纪后期至三叠纪早期，淡水物种以单系群的形式出现。系统发育重建确定了七个主要分支，在志留纪到石炭纪时期经历了早期的多样化。两个主要的进化事件-淡水栖息地的定殖和与海洋真菌的强制性系统共生-标记了这一顺序，导致显著的形态改变，而物种多样化没有相应的增加。尽管新发现的多样性显著，从跨越8亿年的进化时间表来看，现存的分类群多样性似乎相对受到限制。这种限制可能源于有限的地理采样或无性繁殖的普遍性。然而,物种丰富度估计和稀疏分析表明，还没有发现更大的多样性-可能是四倍。这些发现极大地重塑了我们对深异的植物区系Hildenbrandiales物种多样性的理解，并为这种秩序进化史和生态适应提供有价值的见解。在系统发育的支持下，生态和形态学证据，我们建立了Riverina基因。11月。为了适应Hildenbrandiales的淡水物种，在我们的分析中形成了单系进化枝。这标志着完善Hildenbrandiales顺序分类法的第一步，一项要求彻底修改的任务，特别是创建了几个属，以解决Hildenbrandia的多系状态。然而,有限的诊断特征构成了挑战，需要一种新的方法来定义属。一个潜在的解决方案在于拥抱分子系统的观点，可以提供分类边界的精确描述。
