Revision of the genus Dasya (Ceramiales, Rhodophyta) in Galicia (NW Spain) and the addition of a new alien species Dasya sessilis Yamada for the European Atlantic coasts

Abstract

Listen

Translate article

A revision of the genus Dasya in northwestern Iberian Peninsula is presented. Three species (Dasya hutchinsiae, D. ocellata and D. sessilis) are confirmed whilst other three (Dasya corymbifera, D. punicea and D. rigidula) are excluded from the Galician seaweeds flora. The alien species Dasya sessilis Yamada is a new record for the European Atlantic coasts. The study of the herbarium material reveals that D. sessilis was misidentified with other Dasyaceae species and that it has been collected on the Galician coasts for more than 16 years. Morphological and anatomical features of D. sessilis as well as its distribution and chronological data on the Galician coasts are provided. A comparison of the Iberian specimens with the Mediterranean and Asian plants is also included. Dasya sessilis was found growing on a wide range of substrata, from the lower intertidal to subtidal at moderate wave-exposed and sheltered areas. It is abundant in harbours and aquaculture areas together with other alien species such as Heterosiphonia japonica and Undaria pinnatifida. The comparative study between D. sessilis and similar European and Iberian Dasyaceae species is undertaken to prevent further misidentifications. Dasya sessilis is the largest Dasya species, with broader main axes (1-2 mm wide vs 200-500 µm in D. ocellata and 500-600 µm in D. hutchinsiae); pseudolaterals of D. sessilis are 3-5 times pseudodichotomously branched compared to 5-8 times in D. hutchinsiae and 4-5 times in D. ocellata; pseudolateral tips are broader in D. sessilis than in D. ocellata, but smaller than pseudolateral apices of D. hutchinsiae; tetrasporangial stichidium of Dasya sessilis has 6-7 periaxial cells (and 6-7 tetrasporangia) per fertile whorl vs. 4-5 in the rest of the native species; and tetrasporangial stichidia of D. sessilis are longer and cystocarps broader than those in D. hutchinsiae. The alien Dasyaceae species Heterosiphonia japonica, similar in size to Dasya sessilis, differs from it in main axes branching (alternate or distichous in H. japonica vs. spiral in D. sessilis), the number of periaxial cells in the vegetative axes (4 in H. japonica vs. 5 in D. sessilis), and color (pinkish red vs. deep red). Other distinctive characters are the tips of main axes (70-90 µm wide in H. japonica vs. 100-130 µm in D. sessilis), and the diameter of pseudolaterals at the base broader in H. japonica).