Reinstatement of Myelophycus caespitosus Kjellman (Ectocarpales s.l., Phaeophyceae) described from western Japan is proposed based on the comparisons of DNA sequences of Japanese Myelophycus specimens, the type specimen of Chordaria simplex and lectotypified specimen of Myelophycus caespitosus. In the genetic analyses using mitochondrial cox1 and cox3, chloroplast atpB, psbA and rbcL DNA sequences, the specimens morphologically referable to M. simplex formed two distinct clades (clade‐1 and clade‐2) supported by high statistical values. Clade‐1 was distributed on the western coast of Japan (Honshu, Shikoku and Kyushu) from the Kii Peninsula to Tsushima and the Pacific coast of Aomori, northeastern Honshu, and clade‐2 on the Pacific coast of central Honshu from Sanriku to the Kii Peninsula. Based on the cox3 DNA sequences and the location of the type locality at Shimoda, Izu Peninsula, clade‐2 was concluded to correspond to true M. simplex. There were no recognizable differences in the representative morphological features (height and diameter of sporophytes and gametophytes, number of cells comprising cortical, subcortical and medullary layers, thickness of plurilocular gametangia, or length and diameter of unilocular zoidangia) between the specimens included in the two taxa. Analyses of the specimens of the two taxa, including sympatric populations on the Kii Peninsula, using a nuclear genetic marker ocm3 did not suggest any genetic exchanges between the two taxa. On the other hand, cox3 gene sequence of the voucher specimen of Myelophycus caespitosus collected from Goto, Kyushu, western Japan housed in the UPS herbarium was included in clade‐1. In conclusion, we propose the reinstatement of M. caespitosus and to lectotypify the specimen in UPS. Korean Myelophycus specimens reported from Cheju Island and Wando were considered to belong to M. caespitosus based on the reported rbcL sequences.

中文翻译：

---

从日本恢复Myelophycus caespitosus（Scytosiphonaceae，Phaeophyceae）

根据日本髓藻标本、单纯脊索动物的典型标本和 Myelophycus caespitosus 的典型标本的 DNA 序列的比较，建议恢复日本西部描述的 Myelophycus caespitosus Kjellman（Ectocarpales sl，Phaeophyceae）。在使用线粒体 cox1 和 cox3、叶绿体 atpB、psbA 和 rbcL DNA 序列的遗传分析中，形态学上与 M. simplex 相关的标本形成了两个不同的进化枝（进化枝 1 和进化枝 2），并得到了高统计值的支持。Clade-1 分布在日本西海岸（本州、四国和九州）从纪伊半岛到对马和青森太平洋沿岸，本州东北部，而 clade-2 分布在本州中部太平洋海岸从三陆到纪伊半岛。根据 cox3 DNA 序列和类型地点在伊豆半岛下田的位置，推断进化枝 2 对应于真正的 M. simplex。两个样本中的代表性形态特征（孢子体和配子体的高度和直径，包括皮层、皮层下和髓质层的细胞数量，多叶配子体的厚度，或单房结团的长度和直径）没有可识别的差异分类群。使用核遗传标记 ocm3 分析这两个分类群的标本，包括 Kii 半岛的同域种群，并未表明这两个分类群之间有任何遗传交换。另一方面，从九州五岛收集的 Myelophycus caespitosus 凭证标本的 cox3 基因序列，UPS 植物标本馆中的日本西部被包括在 clade-1 中。总之，我们建议恢复 M. caespitosus 并在 UPS 中对标本进行分型。根据报道的 rbcL 序列，从济州岛和莞岛报道的韩国髓藻标本被认为属于 M. caespitosus。