Seaweeds of the South African South Coast
Order Dictyotales
Family Dictyotaceae
Dictyota Lamouroux
Thallus flattened, blades (usually erect) branching (sub-) dichotomously in one plane. Growth by means of a single apical cell. Phaeophycean hairs in scattered tufts. Thallus three cells thick, comprising a single layer of large medullary cells with a single layer of smaller pigmented cortical cells on either side; in some species cell layers may be duplicated in some individuals.
Gametophytes dioecious, oogamous, with reproductive structures exserted; oogonia and antheridia in scattered sori, the latter surrounded by a margin of sterile paraphyses. Sporophytes producing scattered or grouped tetrasporangia, each with 4 non-motile meiospores; sporangia often found with undivided contents.
For further details of most South African species, see Tronchin & De Clerck (2005) and Stegenga et al. (1997). Worldwide, 91 species are currently recognised (Guiry & Guiry 2016), of which 4 are recorded from the South African south coast, including one that appears to be undescribed.
Note: The entity previously known as Dictyota suhrii, (now Rugulopteryx suhrii )can be easily distinguished from south coast Dictyota species by the teeth along its margins.
Key to south coast species
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1a. Branching with a very unequal development of dichotomies; plants therefore appearing to have a flexuous main axis and alternating laterals |
D. liturata |
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1b. Branching with (almost) equal development of dichotomies: plants therefore without a main axis |
2 |
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2a. Plants robust, up to 20 (-35) cm tall, blades to 1 cm wide or wider, iridescent bluish in situ or when fresh |
D. naevosa |
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2b. Plants rather delicate, 1 to 6 (-10) cm tall, blades rarely more than 4 mm wide |
3 |
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3a. Plants small (10-20 mm), erect but often curving downward toward substratum, in situ often with bright green edges; axes 0.5 – 2 mm wide, ca. 80 µm thick |
Dictyota sp1 |
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3b. Thalli erect, up to ca 6 cm tall, a few to 5 mm wide, 100-140 µm thick, from neatly dichotomous (wider forms) to somewhat contorted (narrower forms) |
D. dichotoma |
References Dictyota
M.D. Guiry in Guiry, M.D. & Guiry, G.M. 2016. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 08 March 2016.
Stegenga, H., Bolton, J.J. and R. J. Anderson. 1997. Seaweeds of the South African west coast. Contributions from the Bolus Herbarium 18: 655 pp.
Tronchin, E.M. & De Clerck, O. (2005). Brown algae. Phaeophyceae. Guide to the seaweeds of KwaZulu-Natal. Scripta Botanica Belgica 33: 95-129.
Cite this record as:
Anderson RJ, Stegenga H, Bolton JJ. 2016. Seaweeds of the South African South Coast.
World Wide Web electronic publication, University of Cape Town, http://southafrseaweeds.uct.ac.za; Accessed on 18 November 2024.