Electronic Flora of South Australia Family Fact Sheet
Thallus (sporophyte) erect, much branched, 2–15 cm long, hemi-parasitic on Hormosira banksii (rarely on Xiphophora chondrophylla), attached in or adjacent to the host conceptacles, and with most branches arising as new plants from within the Notheia conceptacles to give a multiple thallus of simple or occasionally branched individuals: true branches occasional in the older axes. Growth from a group of 3 emergent apical cells which segment to produce a central medulla of closely appressed filaments and an outer cortex. Structure largely haplostichous, with occasional intercalary longitudinal cell divisions; outer cortical cells each with several phaeoplasts, without pyrenoids. Phaeophycean hairs absent except within conceptacles.
Reproduction: Conceptacles scattered over the branches, containing both female and male gametangia, the female producing eight macrogametes and the male 64 sperms. Fertilisation occurring only when female gametes have settled on the host or parent plant.
Life history diplontic, anisogamous.
Taxonomic notes: Notheia anomala was studied by Nizamuddin & Womersley (1960) who, having recognised that some truly parenchymatous cell divisions occur and that the female gametangia (referred to as macrozoosporangia) produced motile zooids and not eggs, concluded that it forms a distinctive family which may come within the Chordariales or may justify an order of its own. More recent listings have usually placed Notheia as a family of the Chordariales.
Gibson (1986) has recently clarified the reproduction of Notheia, finding that the larger female gametes become non-motile and attach to the surface of Hormosira or Notheia, but not to other surfaces, and that only attached female gametes attracted the sperms and were fertilised. This unusual situation explains why Nizamuddin & Womersley failed to observe fertilisation of the "zooids", and their occasional observation of "macrozooids" germinating to form filaments may be parthenogenetic development of the female gametes as known in several other brown algae. Formation of zygotes only from female gametes settled on the parent plant conforms with the observation that new branches, interpreted by Nizamuddin & Womersley as new thalli, arise mainly from within conceptacles (providing that fertilisation can occur within conceptacles).
The life-history of Notheia is thus probably diplontic, with anisogametes, and the thallus growth from three apical cells, the largely haplostichous construction, and the presence of conceptacles, prevent Notheia being readily accommodated in any existing order. It hence seems justified to establish the order Notheiales, with the single family Notheiaceae and genus Notheia, for this most unusual alga.
GIBSON, G. (1986). Reproduction of Notheia anomala. Australasian Soc. Phycology and Aquatic Bot., 6th Annual Meeting, Feb. 16–18, 1986. Programme and Abstracts, p. 20.
NIZAMUDDIN, M. & WOMERSLEY, H.B.S. (1960). Structure and systematic position of the Australian brown alga, Notheia anomala. Nature (Lond.) 187, 673–674.
The Marine Benthic Flora of Southern Australia Part II complete list of references.
Womersley, H.B.S. (14 December, 1987)
The Marine Benthic Flora of Southern Australia
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