Electronic Flora of South Australia Genus Fact Sheet

Genus SPOROCHNUS C. Agardh 1817: xii

Phylum Phaeophyta – Order Sporochnales

Thallus (sporophyte) usually 5–50 cm long, with one to several usually percurrent axes or laterals, radially much branched with several orders of branching and the ultimate branches usually of fairly uniform length; some species with long branches bearing only numerous short laterals; each branch with an apical tuft of assimilatory filaments 1–9 mm long, otherwise with a smooth, continuous cortex; attached by a rhizoidal holdfast. Growth apical, with a convex branch meristem surmounted by the apical tuft of assimilatory trichothallic filaments. Structure haplostichous and pseudoparenchymatous, with a core of elongate axial cells and cortex which, in older branches, thickens by periclinal divisions.

Reproduction: Reproduction by unilocular sporangia borne laterally on clavate, branched, multicellular paraphyses (with larger terminal cells) in dense, compact, sori surrounding determinate lateral branches immediately below the apical assimilatory tufts or with a short sterile region below the tufts.

Gametophytes microscopic, filamentous, branched, monoecious or dioecious, oogamous (Caram 1965, p. 146, figs 3–7).

Life history diplohaplontic and heteromorphic.

Type species: S. pedunculatus (Hudson) C. Agardh.

Taxonomic notes: A genus of 10–15 species, widely distributed in temperate waters (extending into the Caribbean), and characterised by the position of the dense, compact, sporangial sori immediately below the apical hair tufts on lateral determinate branches; S. stylosus is unusual in having a short sterile region between the hair tufts and the sporangial receptacles.

References:

AGARDH, C.A. (1817). Synopsis Algarum Scandinaviae. (Lund.)

CARAM, B. (1965). Recherches sur la reproduction et le cycle sexué de quelques Phéophycées. Vie et Milieu 16, 21–222.

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

Author: H.B.S. Womersley

Publication: Womersley, H.B.S. (14 December, 1987)
The Marine Benthic Flora of Southern Australia
Part II
©Board of the Botanic Gardens and State Herbarium, Government of South Australia

KEY TO SPECIES OF SPOROCHNUS

1. Sporangial receptacles separated by a sterile region 1–2 mm long from the apical tufts of assimilatory filaments

S. stylosus

1. Sporangial receptacles immediately adjacent to the apical tufts of assimilatory filaments

2

2. Thallus with long lateral branches bearing only numerous, short (mostly less than 3 mm long), branchlets normally becoming fertile with sporangial receptacles sessile or with pedicels shorter than the length of the receptacle

3

2. Thallus much branched, with branches of several orders and progressively decreasing in length; sporangial receptacles with pedicels distinctly longer than the receptacle length

4

3. Sporangial receptacles sessile, 0.3–2 (–4) mm long, extending from the apical tufts to (and usually just onto) the long laterals

S. apodus

3. Sporangial receptacles 0.2–2 (–5.5) mm long, with a distinct sterile pedicel

S. comosus

4. Thallus very slender (lower branches 400–700 µm in diameter); sporangial receptacles ovoid, becoming linear, 0.5–2 (–3) mm long and 150–250 µm in diameter, with a sterile pedicel 2–20 mm long

S. moorei

4. Thallus moderately slender to robust [lower branches (0.5–) 1–2 mm, becoming 2–3 mm, in diameter]; sporangial receptacles globose to ovoid or clavate, 0.3–1 (–3) mm long and usually 250–700 in diameter, with a sterile pedicel 1–2 (–6) mm long

S. radiciformis


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