Acrosiphonia coalita (Ruprecht) Scagel, Garbary, Golden & M.W.Hawkes

Type locality: Okhotsk Sea, Russia

Etymology: Acrosiphonia (Acro=top, siphonia=tube); coalita (Latin= coalesced).

Common name: Green rope

1. Taxonomy

Ulvophyceae: Ulotrichales: Ulotrichaceae:


Fig. 1. Acrosiphonia coalita – A rope-like cluster of green algal filaments attached to rock in the mid-intertidal at Eagle Cove on San Juan Island. Scale bar = 2 cm.

2. Identification.

Green thallus forming 10-15 cm tall rope-like shape (Fig. 1). Typically, the attached and highly branched plants form rope-like stands as a result of hooked branches (Fig. 2) tangling the thread-like filaments together. More conspicuous forms may reach 40 cm in length. This species can be often found on rocks in the mid and low intertidal in protected to semi-exposed habitats in spring and early summer (see distribution for details).


Fig. 2. Hooked branchlets; reticulate chloroplast; pyrenoids (py). Scale bar = 20 µm.


3. Distribution.

General distribution in North America: Alaska (Scagel et al. 1989, Lindeberg & Lindstrom 2010), Aleutian Islands (Mondragon & Mondragon 2003), British Columbia (Scagel et al. 1989, Saunders & Kucera 2010), California (Scagel et al. 1989, Mondragon & Mondragon 2003, Miller 2012), Oregon (Scagel et al. 1989), Washington (Scagel et al. 1989).

Regional Distribution (based on FHL Herbarium Collection): American Camp Beach, San Juan Island, July 1962; Botany beach, Vancouver Island, May 1989; Cattle Point, San Juan Island, June 1964, March 1983 and June 2013; Dallas beach, San Juan Island, unknown collection date; Eagle Cove 2013; Mara Vista, San Juan Island, April 1989; Minnesota Reef, San Juan Islands, June 1964; Partridge Point, Whidbey Island, April, 1964; South of Deadman Bay, San Juan Island, July, 1955.

First record in FHL Herbarium: July 1955.

4. Vouchers.

Herbarium species and slide housed at FHL Herbarium (under the PHYKOS numbers 000120 and 000121 ).

 5. Research Notes. 

Plants belonging to the genus Acrosiphonia are branched upright uniseriate filaments, each cell having a reticulate chloroplast (Fig. 2). Filaments form 2 (-3) to 10 (-15) cm high cushions, soft and spreading when young, becoming stiff, compact and ropelike in older plants. The plants are attached to substrata by multicellular, branched, down-growing rhizoids issued from the cells in the basal region. Filaments generally increase in diameter towards the apices. Percurrent axes are inconspicuous or absent. The branching is irregular and always intercalary. The branches are usually alternate or opposite, but sometimes more or less unilaterally secund, appressed, with blunt or acute tip, straight or variously incurved and hooked (Fig. 2), entangled. In general, plants are very variable in form depending on age and environmental factors (Jónsson 1999).

Species of Acrosiphonia exhibits an alternation of heteromorphic generations type life history. The haploid phase is a free-living, filamentous plant abundant in the rocky intertidal zone. For the diploid phase of its life history, a unicell colonizes red algae, both blades and crusts (Sussmann & DeWreede 2001). This fact was demonstrated by Sussmann et al. (1999), who showed that DNA sequences of the macrophytic phase were nearly identical to sequences derived from unicellular endophytic green algae present in the red algae Mastocarpus papillatus and Mazzaella splendens.

Concerning the taxonomy, there is a lack of agreement of species boundaries within Acrosiphonia. Criteria commonly used to distinguish species of Acrosiphonia are primarily vegetative characteristics such as diameter of the filaments, length to width ratios of the cells, presence or absence of simple or compound hooks, branching patterns of the plants, shape of the tip cells and number of fertile gamentangia cells in a series (Setchell and Gardner 1920, Scagel 1966). Many of these characteristics are very variable when environmental factors such as light intensity, day length and temperature differ (Kornmann 1965, 1970, Hudson 1974), making species delimitation difficult (Sussmann 2000). For example, Acrosiphonia arcta, a species that occurs in Canada, exhibits distinct morphologies in different environments, thalli from the open-ocean exhibits the typical morphology of profuse, short, curved branches and rhizoids binding the filaments together to form hemispherical to spherical tufts, whereas thalli from sheltered envionments consisted of matted clumps with extensive rhizoidal growth at the base but little branching (Sussmann & Scrosati 2011). Therefore, as with almost every genus of algae, accurate identification of Acrosiphonia requires observation at the molecular level.

Another interesting ecological aspect of this genus is that the sporophytes of some species of Acrosiphonia did not produce zoospores at temperatures ≥15ºC. Hudson (1974) demonstrated that long-day (16h light: 8h dark photoregime) conditions were required for the germination of Acrosiphonia filaments, and growth of gametophytic plants in culture was inhibited at 15–20ºC. This implies seasonality of Acrosiphonia’s gametophyte and is supported by the fact that the gametophytic phase has never been collected in the winter (Sussmann & DeWreede 2001).  The free-living, filamentous gametophytic plants are seasonal, occurring from March-July, with peak percent cover (10%) in April. Plants are fertile immediately after establishment. The unicell, which is the sporophyte phase of Acrosiphonia, aka ‘Chlorochytrium’, and has a spherical shape, colonizes the foliose red alga Mazzaella splendens one month after filamentous Acrosiphonia plants appear. Maximum density was recorded in May. ‘Codiolum,’ on the other hand, is stalked and colonizes the red algal crust Petrocelis. Peak density was recorded 2 months after ‘Chlorochytrium‘ density peaked. The endophytes survive high summer temperatures, which correlate with death of the free-living plants, and overwinter in their hosts. Zoospore release in late winter corresponds to decreased host abundance, suggesting the endophytes have evolved a strategy where duration in the host is synchronized  with host seasonality. Acrosiphonia’s alternate life history allows it to persist in a seasonally variable environment, with the sporophyte phase capable of colonizing two different hosts. (Sussmann & DeWreede 2001).


 6. Literature Cited.

Druehl L. 2000. Pacific seaweeds: A guide to common seaweeds of the West Coast. Harbour Publishing, Madeira Park, B.C.

Jónsson, S. 1999. The status of the Acrosiphoniales (Chlorophyta). Rit Fiskideildar 16: 187–196.

Michael Guiry in Guiry, M.D. & Guiry, G.M. 2013. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway.; searched on 30 June 2013.

Sussmann, A. V., Mable, B. K., Dewreede, R. E. & Berbee, M. L. 1999. Identification of green algal endophytes as the alternate phase of Acro-siphonia (Codiolales, Chlorophyta) using ITSI and ITS2 ribosomal DNA sequence data. Journal of Phycology 35: 607-614.

Sussmann, A. V. 2000. Molecular and field studies of the life history of Acrosiphonia (Codiolales, Chlorophyta). Ph.D. dissertation, University of British Columbia, Vancouver, British Columbia, Canada.

Sussmann, A. V. & Dewreede, R. E. 2001. Life history of Acrosiphonia (Codiolales, Chlorophyta) in southwestern British Columbia, Canada. American Journal of Botany 88:1535–1544.

Sussmann, A. V. & Scrosati, R. A. 2011. Morphological variation in Acrosiphonia arcta (Codiolales, chlorophyta) from environmentally different habitats in Nova Scotia, Canada. Rhodora, Vol. 113, No. 953, pp. 87–105.


7. Links to additional resources.

AlgaeBase images of Acrosiphonia coalita

DNA sequences in Genbank

Phylogeny and Molecular Evolution of Green Algae

8. Page Authors & Affiliations.

Talita Vieira-Pinto, Ph.D. student, Instituto de Biociências, Universidade de São Paulo. Rua do Matão, travessa 14, nº 321, Cidade Universitária, São Paulo – SP, Brazil.