Electronic Flora of South Australia Species Fact Sheet
Phylum Phaeophyta – Order Dictyotales – Family Dictyotaceae – Tribe Zonarieae
Thallus (Fig. 76B) light to medium brown, 10–30 cm long, with one to a few fronds, complanate but becoming twisted and convolute; epiphytic (entangled with Sargassum, Caulocystis and Amphibolis) or probably epilithic with a matted rhizoidal holdfast up to 6 mm across and 1 cm long. Growth (Fig. 771) from few to several apical cells in a slightly depressed apex, with the margin below the branch apices entire or minutely dentate (Fig. 77H). Fronds alternately branched at intervals of 5–20 mm, without proliferous branchlets, mostly 5–10 (–12) mm broad, with a central midrib throughout and lateral branches or lobes to close to the apices, without lateral veins; base of fronds often partly to largely denuded. Structure (Fig. 77K–M) of wing largely monostromatic, 40–65 µm thick, becoming 2 cells thick only near the midrib or near reproductive organs; midrib (6–) 8–15 (–22) cells thick; cells in surface view (20–) 25–35 m across, L/B (1–) 1.5–3 (–4). Hair tufts (Fig. 77H) small, scattered, with hairs (Fig. 77M) arising from small cells cut off laterally from subdivided membrane cells, 20–25 µm in diameter.
Reproduction: Sporangia (Fig. 77J,L) scattered, derived from any cell of the wing, round to ovate in surface view and projecting slightly on both sides of the thallus, (60–) 95–140 µm in diameter, dividing tetrahedrally when mature. Oogonial sori unknown. Antheridial sori (Fig. 77M) scattered, irregular in shape, 200–500 µm long and 100–300 µm across, with not or only slightly enlarged surrounding cells; antheridia 40–60 µm long and 15–30 µm in diameter.
Holotype from D'Estrees Bay, Kangaroo I., S. Aust., drift (Kraft, 14.vii.1972); in ADU, A42542, sporangial.
Distribution: Investigator Strait and the lower Gulfs in South Australia.
Taxonomic notes: Dictyopteris gracilis is distinctive in being the only species with a monostromatic wing and which lacks lateral veins. It appears to be a deep water species, with specimens entangled with or on Amphibolis, Caulocystis and Sargassum, one (A38375) probably epilithic, and the others of uncertain attachment.
References: The Marine Benthic Flora of Southern Australia Part II
Womersley, H.B.S. (14 December, 1987)
The Marine Benthic Flora of Southern Australia
©Board of the Botanic Gardens and State Herbarium, Government of South Australia
Illustrations in Womersley Part II, 1997: FIGS 76B, 77 H–M.
Figure 76 enlarge
Fig. 76. A. Dictyopteris australis (ADU, A50881). B. Dictyopteris gracilis (ADU, A42542, holotype).
Figure 77 enlarge
Fig. 77. A–G. Dictyopteris australis (A,F,G, ADU, A35698; B–D, ADU, A57037; E, ADU, A32543). A. Apex showing central meristem and segmentation. B. Transverse section of margin of thallus. C. Transverse section of thallus with phaeophycean hairs and undivided sporangia. D. Transverse section of midrib and adjacent wing. E. Thallus showing midrib, lateral veins, hair tufts and sporangia. F. Male thallus with antheridial sori. G. Section of male thallus with antheridia. H–M. Dictyopteris gracilis (I–L, ADU, A42542, holotype; H,M, ADU, A38375). H. Apex of thallus with branching midrib and hair tufts. I. Apex showing central meristem and segmentation. J. Apex with tetrasporangia. K. Transverse section of midrib and lateral wing. L. Transverse section of wing and undivided sporangia. M. Transverse section of male thallus with phaeophycean hairs and antheridia.
State Herbarium of South Australia