Macrocystis C.Agardh, 1820: 46
Holotype species: Macrocystis pyrifera (Linnaeus) C.Agardh
Original publication:Agardh, C.A. (1820 '1821'). Species algarum rite cognitae, cum synonymis, differentiis specificis et descriptionibus succinctis. Volumen primum. Pars prima. pp. [i-iv], [1]-168. Lundae [Lund]: ex officina Berlingiana.
Download PDF
Taxonomic status: currently recognized as a distinct genus.
Description: Thallus to 45 m long, perennial, typically 4-8 years. Holdfast conical and consisting of a few central erect stipes bearing terete branching haptera; or holdfast prostrate, subligulate, branched, creeping with short haptera along lateral margins. Stipes numerous, erect, terete, dichotomously branching 2-6 times near base. Each stipe branch subtends a frond, which is composed of a stipe with attached blades and an apical meristematic blade. Apical blade falcate, with several young lateral blades produced unilaterally by splitting through transition region. Blades numerous on each stipe, arranged at regular intervals with a short stipe and a pyriform to subglobose pneumatocyst subtending an undivided lamina, which is narrow to broad with tapering ends, smooth to rugose, and with denticulate margins. Spores produced in unilocular sporangia with paraphyses on sporophylls borne on stipe near holdfast, with sporangia covering most of both surfaces. Sporophylls divide several times dichotomously, with or without pneumatocyst. Gametophytes dimorphic, dioecious, oogamous, branched uniseriate filaments.
Comments: Macrocystis species occur in both the Northern and Southern Hemispheres, occurring along the Pacific coast of North America in the north and having a cicumsubantarctic distribution in the south. Many species were described based on morphological differences, later reduced to species based mainly on holdfast morphology. Two species, M. pyrifera and M. integrifolia Bory, are reported from both Northern and Southern Hemispheres while M. angustifolia Bory is only reported to occur in the Southern Hemisphere. M. angustifolia Northern hemisphere phase, as described by Neushul (1971) for southern California, is recognized by some to be conspecific with M. pyrifera (Abbott and Hollenberg 1976), or as M. pyrifera var. californica (Brostoff 1988).
Northern Hemisphere species are interfertile, with hybrids producing viable spores. Southern Hemisphere and Northern Hemisphere species also hybridize in laboratory trials, but reproductive viability was not tested.
A new species, M. laevis Hay (1986) was described from Marion Island in the southern Indian Ocean, based on plants there having smooth blades, but the recognition of this entity as a separate species is doubtful.
M. integrifolia and M. pyrifera have a haploid number of 16 or 32 chromosomes, with the polyploid number reported in one case from each species. The fronds (stipe with attached blades) of a Macrocystis plant are ephemeral, with a life span of approximately 6 months. A young frond grows to the surface, with new blades being formed at regular intervals. After the frond reaches the surface, growth continues for a short time, forming a dense surface canopy, followed by cessation of new blade formation and finally senescence. Mature fronds at the surface produce excess photosynthate which is translocated to the holdfast and used in initiating new frond growth.
Macrocystis plants experience a wide variety of environmental conditions because of their perennial nature, their growth habit reaching from deeper water to the surface, and their wide geographic distribution.
The physiology of Macrocystis has been widely studied in these various situations, particularly in Northern Hemisphere populations, including studies of photosynthesis and nutrient uptake kinetics. Light and nutrient requirements for recruitment of young Macrocystis plants have been determined for M. pyrifera in southern California. These data have been used to model the growth of M. pyrifera individuals and populations in response to these complex factors. Ecotypic differentiation of nitrogen physiology has been found between populations of M. pyrifera from different localities of California.
Macrocystis is of both economic and ecological importance. Between 100,000 and 170,000 wet tons of Macrocystis were harvested annually in California for alginate extraction and abalone feed, but this alginate production has now ceased, although plants are still harvested for abalone. Sustainable harvesting is important as the organisms that thrive in Macrocystis forest communities are of great value aesthetically, supporting both commercial fishing operations and recreational activities, particularly SCUBA.
NCBI Nucleotide Sequences
Numbers of names and species: There are 18 species (and infraspecific) names in the database at present, of which 1 has been flagged as currently accepted taxonomically.
Names: ('C' indicates a name that is currently accepted taxonomically; 'S' a homotypic or heterotypic synonym; 'U' indicates a name of uncertain taxonomic status, but which has been subjected to some verification nomenclaturally; 'P' indicates a preliminary AlgaeBase entry that has not been subjected to any kind of verification. For more information on a species click on it to activate a link to the Species database):
Macrocystis angustifolia Bory de Saint-Vincent S
Macrocystis communis Bory de Saint-Vincent S
Macrocystis humboldtii (Bonpland) C.Agardh S
Macrocystis integrifolia Bory de Saint-Vincent S
Macrocystis laevis C.H.Hay S
Macrocystis latifolia Bory de Saint-Vincent S
Macrocystis luxurians (J.D.Hooker & Harvey) J.Agardh S
Macrocystis menziesii (Turner) C.Agardh S
Macrocystis obtusa Harvey S
Macrocystis orbigniana Montagne S
Macrocystis pelagica Areschoug S
Macrocystis planicaulis C.Agardh S
Macrocystis pomifera Bory de Saint-Vincent C
Macrocystis pyrifera var. humboldtii Bonpland S
Macrocystis pyrifera (Linnaeus) C.Agardh C - type
Macrocystis pyrifera var. luxurians J.D.Hooker & Harvey S
Macrocystis pyrifera var. longibullata Reinsch C
Macrocystis tenuifolia Postels & Ruprecht S
Contributors
Some of the descriptions included in AlgaeBase were originally from the unpublished Encyclopedia of Algal Genera,
organised in the 1990s by Dr Bruce Parker on behalf of the Phycological Society of America (PSA)
and intended to be published in CD format.
These AlgaeBase descriptions are now being continually updated, and each current contributor is identified above.
The PSA and AlgaeBase warmly acknowledge the generosity of all past and present contributors and particularly the work of Dr Parker.
Descriptions of chrysophyte genera were subsequently published in J. Kristiansen & H.R. Preisig (eds.). 2001. Encyclopedia of Chrysophyte Genera. Bibliotheca Phycologica 110: 1-260.
Linking to this page: http://www.algaebase.org/search/genus/detail/?genus_id=35715
Citing AlgaeBase
Cite this record as:
Guiry, M.D. & Guiry, G.M. 2013. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 20 June 2013.
Algaebase taxon LSID: urn:lsid:algaebase.org:taxname:8089
