Electronic Flora of South Australia Family Fact Sheet
Phylum Phaeophyta – Order Dictyotales
Thallus complanate, dichotomous to laterally branched. Growth from a lenticular apical cell within an apical depression, orientated lengthwise to the branch, segmenting on two lateral faces, with the blade becoming three cells thick, then 3–5 cells thick with a central layer of large medullary cells, finally 8–12 cells thick with a single layered outer cortex of densely phaeoplastic cells and medulla 6–10 cells thick of large, clear cells. Hair tufts scattered, phaeophycean, derived from groups of cortical cells.
Reproduction: Sporangial and oogonial plants unknown. Male plants with scattered sori of antheridia, surrounded by elongate sterile paraphyses, formed from cortical cells of the thallus.
Type and only genus: Scoresbyella Womersley.
Taxonomic notes: The genus Scoresbyella is only known from sterile collections and one male plant. The latter supports placement in the Dictyotales since the antheridial sori are typical of this order, being on the surface and surrounded by sterile cells as in many Dictyoteae.
However, the single apical cell in each branch shows a different orientation to that of the Dictyoteae, lying longitudinally and cutting off cells laterally from two faces, not from one basal side as in the Dictyoteae. Further segmentation of the two derivative cells is similar to the single derivative of Dictyoteae, but later segmentation and cell arrangement becomes more irregular.
It is therefore necessary to place Scoresbyella in a separate family within the Dictyotales.
References: The Marine Benthic Flora of Southern Australia Part II
Womersley, H.B.S. (14 December, 1987)
The Marine Benthic Flora of Southern Australia
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State Herbarium of South Australia