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Semnocarpa minuta Huisman, Foard & Kraft 1993: 148, figs 18–30

Phylum Rhodophyta – Class Florideophyceae – Order Rhodymeniales – Family Lomentariaceae

Thallus 1–10 (–30) mm high, with one to several simple or branched terete axes, elongate-clavate and saccate, branches ovoid to clavate, basally constricted, apices rounded; axes and branches 0.5–1 mm in diameter. Holdfast (Fig. 61C) monostromatic, 0.3–0.8 mm across; epiphytic on various algae. Structure multiaxial, with a group of short apical filaments producing the network of medullary filaments bearing secretory cells and cutting off outwardly the layer of large, ovoid, inner medullary cells 20–35 µm in diameter and an outer cortex 1–2 cells thick of small ovoid cells 4–6 µm in diameter. Holdfast cells ovoid, 8–12 µm in diameter. Rhodoplasts discoid, in chains in inner cells.

Reproduction: Gametangial thalli dioecious. Carpogonial branches 3-celled, borne on inner cortical cells together with a 2-celled auxiliary cell branch, auxiliary cell with a proteinaceous globule. Carposporophyte (Fig. 61D) developing within the branch cavity, producing several lobes with all cells forming ovoid carposporangia 8–12 µm in diameter, surrounded by an involucre of relatively coarse filaments connected to the auxiliary cell initial and adjacent cortical filaments. Cystocarps completely immersed, projecting into the cavity, with a small cortical ostiole. Spermatangia in sori near the branch apices, cut off from initials on the outer cortical cells, elongate-ovoid, 3–6 µm in diameter.

Tetrasporangia (Fig. 61E) in depressed sori, cut off thallus inwardly from cortical cells lining the depression, subspherical to ovoid, 120–135 µm in diameter, tetrahedrally divided.

Type from Green I., Rottnest I., W. Aust., epiphytic on Rhodopeltis borealis (Kraft & Huisman, 3.x.1990); holotype in MELU, A40100.

Selected specimens: Seamount off Cannan Reefs, S. Aust., 22–30 m deep on Dictyota prolifera (Branden, 22.i.1991; AD, A61202). Vivonne Bay, Kangaroo I., S. Aust., on Rhodymenia australis, 1–4 m deep on jetty piles (Kraft, 6.iv.1972; AD, A42379). Margaret Brock Reef, Cape Jaffa, S. Aust., on Craspedocarpus venosus, 3–5 m deep (R.K. Lewis, 29.xi.1972; AD, A42927). Eaglehawk Neck, Tas., on Carpopeltis phyllophora, 12–21 m deep (Kraft 9655, 12.xii.1993; AD, A63397 and MELU).

Distribution map based
on current data relating to
specimens held in the
State Herbarium of SA

Distribution: Port Denison, W. Aust., to Margaret Brock Reef, Cape Jaffa, S. Aust., and Eaglehawk Neck, Tas. Probably more widely distributed but easily overlooked.

Taxonomic notes: S. minuta was described from the west coast of Western Australia, but isolated collections are known from southern Australia and it may be more plentiful than presently indicated. It was described as epiphytic on Rhodopeltis, Amphibolis, Halimeda and Hennedya, and apparently occurs on several firm-surfaced red algae.

Thalli only 1 mm long are usually reproductive.

References: The Marine Benthic Flora of Southern Australia Part IIIB

Author: H.B.S. Womersley

Publication: Womersley, H.B.S. (28 June, 1996)
The Marine Benthic Flora of Southern Australia
Rhodophyta. Part IIIB. Gracilarialse, Rhodymeniales, Corallinales and Bonnemaisoniales
Reproduced with permission from The Marine Benthic Flora of Southern Australia Part IIIB 1996, by H.B.S. Womersley. Australian Biological Resources Study, Canberra. Copyright Commonwealth of Australia.

Illustration in Womersley Part IIIA, 1996: FIG. 61 C–E.

Figure 61 image

Figure 61   enlarge

Fig. 61. A, B. Semnocarpa corynephora (AD, A33693). A. Surface view of tetrasporangial sori. B. Section of branch with tetrasporangial sori, the lower one without tetrasporangia. C–E. Semnocarpa minuta (C, AD, A42379; D, AD, A42927; E, AD, A61202). C. Longitudinal section of thallus on Rhodymenia. D. Section of a cystocarp, with basal fusion cell, erect filaments and carposporangia. E. Thallus with tetrasporangia.

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