SYSTEMATICS OF THE CALCIFIED GENERA OF THE GALAXAURACEAE (NEMALIALES, RHODOPHYTA) WITH AN EMPHASIS ON TAIWAN SPECIES¹

Abstract

The current separation of the calcified genera Actinotrichia Decaisne, Galaxaura Lamouroux, and Tricleocarpa Huisman et Borowitzka in the Galaxauraceae is largely based on type of life history (whether the gametophytes and tetrasporophytes are isomorphic or heteromorphic with respect to gross morphology or cortical-cell features) and on features of postfertilization development (such as the composition of the pericarp). We reexamined the phylogenetic relationships of these genera based on comparative rbcL sequence analysis, types of life cycle, and cystocarp development. Four distinct assemblages have been identified: an Actinotrichia clade, a Tricleocarpa clade, a Galaxaura clade (containing the type species), and a Dichotomaria clade made of a number of formerly Galaxaura species (D. obtusata [Ellis et Solander] Lamarck, D. marginata [Ellis et Solander] Lamarck, and D. diesingiana [Zanardini] Huisman, Harper and Saunders). Key differences between Dichotomaria and Galaxaura include the habit of the gametophytic and tetrasporophytic generations (isomorphic in Dichotomaria and dimorphic in Galaxaura) as well as the presence or absence of a persistent pericarp in the cystocarp (present in Dichotomaria and absent in Galaxaura). Molecular data do not support monophyly for the putatively pantropical species Galaxaura rugosa, Dichotomaria obtusata, and D. marginata, all of which we conclude are in need of taxonomic revision.

First record of Dichotomaria obtusata (Ellis & Solander) Lamarck (Nemaliales, Rhodophyta) in the Mediterranean Sea

“…Borowitzka, with over 50 species currently accepted (Guiry & Guiry, 2014). Dichotomaria was reestablished as distinct from Galaxaura by Huisman et al (2004) on the basis of morphological and molecular evidence, and this segregation was further supported by new morphological characters (Wang et al, 2005). Within Galaxauraceae, Dichotomaria is characterized by having ± isomorphic gametophytic and tetrasporophytic phases, a pericarp enclosing the cystocarp, a multinucleate fusion cell formed by gonimoblast cells, and cruciately divided tetrasporangia produced on stalk cells (Wang et al, 2005;Wiriyadamrikul et al, 2014).…”

“…Digital images were acquired with an Olympus DP71 microscope digital camera and an Olympus SP 820UZ digital camera (Olympus Corp. Tokyo, Japan). We compared the anatomical and cellular features of the Mediterranean specimens of Dichotomaria to those published in the literature (Littler & Littler, 2000;Wang et al, 2005;Wiriyadamrikul et al, 2014), and also to Dichotomaria specimens stored at the national seaweed herbaria of Israel.…”

Notes on the marine algae of the Bermudas. 15. Dichotomaria huismanii (Galaxauraceae, Rhodophyta), a new species in the D. marginata complex from the western Atlantic

“…Finally, G. tenera was resurrected as Dichotomaria tenera by Huisman et al (2004) based on LSU sequence data (and the morphology of terminal cortical cells) of specimens from South Africa. It seems obvious from these convoluted pathways that historical taxonomic decisions involving Galaxaura and Dichotomaria species need to be reassessed from the fresh perspective of DNA sequencing, as has been done in selected recent studies (Huisman et al 2004, Wang et al 2005, Kurihara and Huisman 2006, Wiriyadamrikul et al 2014. Accordingly, what has been combined in the past under D. marginata, has already begun fragmenting back to a greater number of species.…”

“…For example, prior to the availability of molecular sequencing and comparison of species, used Pacific Costa Rican samples of G. stupocaulon Kjellman (type locality = Brazil) to characterize this species, and make comparisons with other members that would be included in the D. marginata complex today (Huisman et al 2004, Wang et al 2005, Kurihara and Huisman 2006, Wiriyadamrikul et al 2014. Oliveira (1977) noted the "great similarity" of Galaxaura angustifrons Kjellman (type locality = Brazil) from Brazil to G. veprecula Kjellman (type locality = Madagascar) from the Philippines and Ecuador based on Chou's (1947) observations and measurements.…”

“…Lamouroux, and all subsequent reports in Bermuda followed their lead (see Schneider 2003). In the present study, we have made several recent collections of D. marginata in Bermuda and St. Croix, Virgin Is., to compare genetically with other species in the complex, in particular specimens attributed to this species from Puerto Rico analyzed by Huisman et al (2004) and Guadeloupe by Wang et al (2005) and Wiriyadamrikul et al (2014).…”