Oceanic islands have been recognized as natural laboratories in which to study a great variety of evolutionary processes. One such process is evolutionary radiations, the diversification of a single ancestor into a number of species that inhabit different environments and differ in the traits that allow them to exploit those environments. The factors that drive evolutionary radiations have been studied for decades in charismatic organisms such as birds or lizards, but are lacking in lichen-forming fungi, despite recent reports of some lineages showing diversification patterns congruent with radiation. Here we propose the Ramalina decipiens group as a model system in which to carry out such studies. This group is currently thought to be comprised of five saxicolous species, all of them endemic to the Macaronesian region (the Azores, Madeira, Selvagens, Canary and Cape Verde islands). Three species are single-island endemics (a rare geographic distribution pattern in lichens), whereas two are widespread and show extreme morphological variation. The latter are suspected to harbor unrecognized species-level lineages. In order to use the Ramalina decipiens group as a model system it is necessary to resolve the group's phylogeny and to clarify its species boundaries. In this study we attempt to do so following an integrative taxonomy approach. We constructed a phylogenetic tree based on six molecular markers, four of which are newly developed and generated competing species hypotheses based on molecular (species discovery strategies based on both single locus and multilocus datasets) and phenotypic data (unsupervised clustering algorithms based on morphology, secondary chemistry and geographic origin). We found that taxonomic diversity in the Ramalina decipiens group has been highly underestimated in previous studies. In consequence, we describe six new species, most of them single-island endemics and provide a key to the group. Phylogenetic relationships among species have been reconstructed with almost full support which, coupled with the endemic character of the group, makes it an excellent system for the study of island radiations in lichen-forming fungi. Citation: Blázquez M, Pérez-Vargas I, Garrido-Benavent I, et al. 2024. Endless forms most frustrating: disentangling species boundaries in the Ramalina decipiens group (Lecanoromycetes, Ascomycota), with the description of six new species and a key to the group. Persoonia 52: 44-93. https://doi.org/10.3767/persoonia.2024.52.03 .

Keywords: Macaronesia; island; lichen; new taxa; radiation; species delimitation.

© 2024 Naturalis Biodiversity Center & Westerdijk Fungal Biodiversity Institute.

海洋岛屿被公认为是研究各种进化过程的天然实验室。其中一种进化过程就是辐射演化，即一个单一祖先物种分化成多个不同环境下的物种，并在利用这些环境的特征上有所不同。数十年来，人们一直对鸟类或蜥蜴等迷人生物体中的驱动因素进行研究，但在地衣形成真菌中却缺乏相关研究，尽管最近有报道称一些谱系显示出与辐射演化相一致的多样化模式。在这里，我们建议将Ramalina decipiens组作为此类研究的模型系统。目前认为该组包含五个岩生物种，所有这些物种都是大西洋群岛（亚速尔群岛、马德拉群岛、塞尔瓦根群岛、加那利群岛和佛得角群岛）特有的。其中三个物种是单一岛屿特有种（在地衣中极为罕见的地理分布模式），而另外两个物种则广泛分布并表现出极端形态变化，疑似藏有未被识别的物种级谱系。为了将Ramalina decipiens组用作模型系统，有必要解析该群的系统发育关系并澄清其物种界限。在此研究中，我们采用综合分类学方法尝试这样做。基于六个分子标记（其中四个为新开发）构建了一个系统发育树，并根据分子数据（基于单基因座和多基因座位的数据集进行物种发现策略）和表型数据（基于形态、次级化学成分及地理来源的无监督聚类算法）生成了竞争性物种假设。我们发现，在Ramalina decipiens组中的分类多样性在先前的研究中被严重低估。因此，我们描述了六个新物种，其中大多数是单一岛屿特有种，并提供了该群的鉴别表。物种间的系统发育关系已几乎完全得到支持，结合这一群体特有的岛屿特性，使其成为研究地衣形成真菌岛辐射演化的极佳模型系统。引用：Blázquez M, Pérez-Vargas I, Garrido-Benavent I, et al. 2024. Endless forms most frustrating: disentangling species boundaries in the Ramalina decipiens group (Lecanoromycetes, Ascomycota), with the description of six new species and a key to the group. Persoonia 52: 44-93. https://doi.org/10.3767/persoonia.2024.52.03.

关键词： 大西洋群岛；岛屿；地衣；新物种；辐射演化；物种界定。

© 2024 Naturalis Biodiversity Center & Westerdijk Fungal Biodiversity Institute.