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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

1a. Branching with a very unequal development of dichotomies; plants therefore appearing to have a flexuous main axis and alternating laterals

D. liturata

1b. Branching with (almost) equal development of dichotomies: plants therefore without a main axis

2

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

2b. Plants rather delicate, 1 to 6 (-10) cm tall, blades rarely more than 4 mm wide

3

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

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 21 November 2018.