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Order Acrochaetiales

Family Acrochaetiaceae

Genus Acrochaetium Naegeli

Description from Stegenga et al. (1997): “Plants filamentous. Cells with a central stellate chloroplast and a central pyrenoid. Unicellular hairs occurring frequently. Life history triphasic, heteromorphic. Gametophytes with a single basal cell and one to six erect axes; tetrasporophytes with a multicellular base originating from a septately germinated spore, and with several erect axes.

In the field it is often difficult to recognise the different generations as belonging to the same life history, and in the past they have received different names. We have synonymised such “species” that have been shown to belong to the same life history when grown in culture.”

Almost 200 species are recognised worldwide (Guiry & Guiry 2014), among which 6 are recorded from the south coast of South Africa.

Note: Stegenga (1985) published a detailed account of South African Acrochaetiaceae, including most of the Acrochaetium species covered here. In that account and in Stegenga et al (1997) the genera Audouinella and Colaconema were treated as members of the Acrochaetiaceae, but the molecular study of Harper & Saunders (2002) subsequently erected the Order Colaconematales and Family Colaconemataceae to accommodate both these genera in the genus Colaconema.

Acrochaetium is distinguished from the superficially similar genus Colaconema by having a single axial stellate chloroplast per cell with one central pyrenoid.

Key to the species

 

1a. Thalli almost completely endophytic, only reproductive cells protruding from the host; pattern of spore germination usually not detectable

A. brebneri

1b. Thalli mainly epiphytic; in young plants a typical septate pattern of spore germination is detectable (in the tetrasporophyte; gametophytes with a unicellular base)

2

2a. Thalli minute, erect filaments up to 6 cells long; to 6 µm in diameter

A. reductum

2b. Mature erect thalli more than 6 cells long, filaments 7-12 µm in diameter

3

3a. Monosporangia in terminal or lateral-secund, catenate series of 2-4

A. catenulatum

3b. Monosporangia usually single; secund, lateral or terminal

4

4a. Cells in middle of erect axes 7-7.5 µm in diameter; septation pattern of germinating spore 4-celled

A. hlulekaense

4b. Cells in middle of erect axes 8-10 µm in diameter; septation pattern of germinating spore either 2- or 3-celled

5

5a. Monosporangia 19-22 µm long; septation pattern of germinating spore 3-celled; cells in middle of erect axes 8-10 µm in diameter

A. tenuissimum

5b. Monosporangia less than 15 µm long; septation pattern of germinating spore 2-celled

A. moniliforme

 

References Acrochaetium

Guiry, M.D. & Guiry, G.M. 2014. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 21 October 2014.

Harper, J.T. & Saunders, G.W. 2002. A re-classification of the Acrochaetiales based on molecular and morphological data, and establishment of the Colaconematales, ord. nov.. British Phycological Journal 37: 463-475.

Stegenga, H. 1985. The marine Acrochaetiaceae (Rhodophyta) of southern Africa. South African Journal of Botany 51: 291-330, 25 figs, 1 table.

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.

 

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 20 November 2018.