Electronic Flora of South Australia Genus Fact Sheet

Genus AMOENOTHAMNION Wollaston 1968: 376

Phylum Rhodophyta – Order Ceramiales – Family Ceramiaceae – Tribe Heterothamnieae

Thallus erect, with subdichotomous axes bearing separated whorls of 3–5 relatively short whorl-branchlets from the upper ends of axial cells; whorl-branchlets usually branched from their basal cells, often with terminal hairs; gland cells absent or lateral on outer cells. Attachment by rhizoids from basal cells, but without penetration of host; epiphytic (or free floating). Lateral branches arising close to apices, from subapical cells and axes becoming subdichotomous. Cells uninucleate.

Reproduction: Gametophytes dioecious. Procarps borne on the basal cells of 1–3 reduced whorl-branchlets near branch apices, with the basal cell acting as the supporting cell for the 4-celled carpogonial branch. Post-fertilization a terminal and 2–3 lateral gonimolobes are produced, with only loose involucral branches from below. Spermatangia occur on special short branches on basal cells of whorl-branchlets.

Tetrasporangia occur on lower cells of whorl-branchlets, sessile, obliquely tetrahedrally divided.

Type species: Amoenothamnion planktonicum Wollaston 1968: 377, fig. 35D–Q, pl. 10.

Taxonomic notes: Wollaston (1968) included 3 newly described species in Amoenothamnion, one of which (Am. elongatum = L. fastigiatum (Harvey) Womersley, comb. nov.) has been separated by Athanasiadis (1996, p. 183) in a separate genus Leptoklonion. A further species, Amoenothamnion lycopodioides Stegenga (1986, p. 10) has been described from South Africa.

Leptoklonion was separated by Athanasiadis (1996, p. 183) on the basis of 2-celled whorl-branchlets bearing procarps, development of secondary axes in place of whorl-branchlets, and development of tetrasporangia on protrusions of the basal cells of whorl-branchlets. However, 2-celled fertile whorl-branchlets comprise only a slight reduction of the short whorl-branchlets in Am. planktonicum, the lateral (secondary) axes in Am. planktonicum arise from apical cells above the whorl-branchlets or (in female plants) from the basal cells of whorl-branchlets, and degree of protrusion of the cell bearing the tetrasporangium is variable (Wollaston 1968, figs 36F–H). Further study is necessary of these differences.

References:

ATHANASIADIS, A. (1996). Morphology and classification of the Ceramioideae (Rhodophyta) based on phylogenetic principles. Opera Botanica No. 128, pp. 1–216.

STEGENGA, H. (1986). The Ceramiaceae (excl. Ceramium) (Rhodophyta) of the South West Cape Province, South Africa. Bibl. Phycol. 74, 1–149.

WOLLASTON, E.M. (1968).Morphology and taxonomy of southern Australian genera of Crouanieae Schmitz (Ceramiaceae, Rhodophyta). Aust. J. Bot. 16, 217–417.

The Marine Benthic Flora of Southern Australia Part IIIC complete list of references.

Author: H.B.S. Womersley & E.M. Wollaston

Publication: Womersley, H.B.S. (24 December, 1998)
The Marine Benthic Flora of Southern Australia
Rhodophyta. Part IIIC. Ceramiales – Ceramiaceae, Dasyaceae
©State Herbarium of South Australia, Government of South Australia

KEY TO SPECIES OF AMOENOTHAMNION

1. Axial cells 120–180 (–220) µm in diameter and L/D 1–2 (–2.5); whorl-branchlets 60–90 µm long, with large, rounded, basal cells bearing usually 3 branches, 4–7 cells long, terminal cells acute; gland cells absent	Am. planktonicum
1. Axial cells 60–100 µm in diameter and L/D 1–2 (–2.5); whorl-branchlets (90–) 100–150 µm long, with rounded to elongate basal cells bearing 2–4 branches, terminal cells acute; gland cells usually present but sparse	Am. minimum

Email Contact:
State Herbarium of South Australia