한국산 홑파래과 해조류의 계통 및 분류

Abstract

The family Monostromataceae Kunieda, which was erected based on culture studies of Monostroma latissimum Wittrock and M. nitidum Wittrock, is circumscribed by the presence of filament stage in thallus ontogeny, swarmer release by wall dissolution, biflagellate and phototactic swarmer released from the leafy thallus, the presence of non-shell boring Codiolum-sporophyte in the sexual life cycle, and obligatory intertidal habitat. This family currently include several genera including Monostroma Thuret which has been traditionally recognized as single cell-layered taxa with blade-like thallus. The taxonomic groups in the Monostromataceae have been distinguished largely based on morphological features in addition to life cycle, developmental characteristics and gametangial/zoidangial structure. This, with lack of a clear cut systematic placement of this Ulvophycean group, was caused by various and often contradictory taxonomic revisions. Therefore, this study was carried out with the purpose of acquiring a better understanding of the phylogeny and taxonomy of the family. For this, 17 species belonging to the family were collected from various localities in Korea, and were analyzed based on morphological, ontogenetic and molecular data. In a phylogenetic tree based on ITS, Monostromataceae formed four distinct major clades with a genetic distance of 6.8 to 38.2%. However, they were not monophyletic. A filamentous green alga collected from the eastern and the southern coast of Korea is morphologically characterized by 5-10 cm high, non-branching filamentous thallus attached by rhizoidal cell to any coarse substratum in middle to upper intertidal zones and girdle-shaped chloroplast with several round pyrenoids. In the phylogenetic tree based on ITS sequences, the Korean alga, with intraspecific distance of 4.5%, nests in a same clade with Ulothrix flacca Thuret which has been located far from U. mucosa Thuret, type of the genus. The phylogenetic position and morphological features suggest that Ulothrix flacca should be separated from Ulothrix Thuret and Monostroma Thuret, respectively. Accordingly, Paraulothrix flacca (Thuret) gen. et comb. nov. is proposed for this Korean alga based on the morphological and molecular analyses. A green alga, which has formed the same clade as the Monostroma species, is morphologically characterized by foliose, monostromatic, soft textured thallus and usually undulate and entire margins. Cells in the surface view are often arranged in pairs, rectangular to polygonal near the middle to upper portion, but oval to rectangular with round corners near the basal portion. Each chloroplast is cap-like shape and has 2-3 pyrenoids. The Korean alga, with interspecific genetic divergence of 4.6%, appears to be distinguishable mainly from similar species by these chloroplast features. For this Korean entity, Monostroma honghyeonriensis sp. nov. is described based on the morphological and molecular data. Another monostromatic green alga, which was collected from Sajin-ri located on the eastern coast of Korea, is morphologically characterized by foliose, monostromatic, soft textured thallus with size up to 30 cm. Blades range from 25 to 40 μm in thickness, ovate to lanceolate and simple to lobed. They are attached by a discoid holdfast to rocks in intertidal zones, and have no serrations in blade margin. Cells are usually arranged in pairs, rectangular to polygonal near the middle to upper portion, and oval to rectangular with round corners near the basal portion in the surface view. A cap-like chloroplast has 2-3 pyrenoids. This species appears to be distinct from similar species by the relatively thick thallus, cell shape and number of pyrenoids per chloroplast. In a phylogenetic tree based on ITS, sequences from the Korean entity nest in a same clade with Gayralia oxysperma (Kützing) K.L.Vinogradova ex Scagel et al. described originally from Baltic Sea, Germany, with an interspecific divergence of 3.8%. Based on morphological and molecular data, Gayralia sajinriensis sp. nov. is proposed for this Korean alga. In conclusion, taxonomic characters and phylogeny of the Monostromataceae from Korea were evaluated, and one new genus with a resulting combination species and two new species were included based on this. In addition, a key to the Korean species within the family was presented.