Dictyota dimorphosa

Belleza, Dominic Franco C., Tateishi, Hiroto, Tanimae, Shin-Ichiro, Kobayashi, Taishun, Aota, Tomoyuki, Urasawa, Toshiki & Nishihara, Gregory N., 2025, An annotated list of brown seaweeds (Phaeophyceae) from Nakadori Island (northern Goto Islands, Nagasaki, Japan), Phytotaxa 694 (1), pp. 1-24 : 8-9

* Dictyota dimorphosa Ni-Ni-Win & Kawai, 2024

Japanese name: アミジグサ (amijigusa)

Type locality: —Reihoku, Amakusa, Kumamoto Prefecture, Japan

Description and remarks: —Specimens are 3–7 cm tall measured from the small rhizoidal holdfast up to the apices. The specimens show increasing thallus width from the base (3–4 mm) to the upper branches (8–9 mm). Branches are dichotomous with broad and obtuse tips. This species was collected at Yokoura, Naname, and at the old and new ports of Mushima. Specimens here can be considered small and presumably juvenile as their collection was done in the early part of the spring seaweed bloom in Japan ( Choi et al. 2002) compared to more mature specimens ( Hörnig & Schnetter 1988).

This species has a very close resemblance with D. dichotoma , a species which has a wide geographic distribution, from the Northern Atlantic ( van den Hoek 1982) to the tropics ( Titlyanov et al. 2015, Phang et al. 2016, Lastimoso & Santiañez 2021). Its morphological variability has been discussed in the Dictyota dichotoma complex ( Hörnig & Schnetter 1988). A study using a molecular approach show that D. dichotoma and D. implexa have a wider distribution unlike other European species (i.e., D. fasciola , D. mediterranea , D. spiralis , D. cyanoloma ) which are restricted to the northeastern Atlantic ( Tronholm et al. 2010). An earlier paper suggested that two D. dichotoma morphotypes from Korea as being a single species based on molecular analyses despite having differences in anatomical characteristics ( Hwang et al. 2005). However, a recent paper suggests that the previously described D. dichotoma from Korea, along with representatives from Japan may actually be a new species, Dictyota dimorphosa (Ni-Ni-Win et al. 2024) based on a combination of morphological and molecular evidence. In our case, we did not include molecular methods to ascertain the identity of our specimens but the gross morphology seem to match those described by Ni-Ni-Win et al. (2024). For example, our specimens have dichotomous branching that extend in a straight direction throughout the length of the branch, while in the field, we also observed a slight iridescence in live samples. Since it is likely that the D. dichotoma in Japan may be based on misapplied names ( Tronholm et al. 2010, Ni-Ni-Win et al. 2024), D. dimorphosa is the most plausible species epithet to our samples.

Materials examined: —18ECS1-33 (1 to 21) and 18ECS1-114-1