Electronic Flora of South Australia Genus Fact Sheet

Genus DILOPHUS J. Agardh 1882: 106

Phylum Phaeophyta – Order Dictyotales – Family Dictyotaceae – Tribe Dictyoteae

Thallus dichotomous or becoming irregularly laterally branched, complanate or with twisted branches, 2–25 cm long with branches 1–15 (–20) mm broad, axils usually rounded, basally attached by rhizoids or stolons; proliferations usually few to absent, in some taxa occasionally profuse; surface of branches smooth. Growth by a single apical cell, usually slightly protruding, segmenting by transverse and then longitudinal walls to form a large-celled medulla 1–4 (–6) cells thick in the central region of the branch, 2–6 cells thick near the margins, with a monostromatic small-celled cortex. Phaeoplasts numerous in each cortical cell, discoid. Phaeophycean hairs present as scattered tufts.

Reproduction: Tetrasporangia, oogonial sort and antheridial sori scattered over the thallus surface or grouped into patches.

Life history diplohaplontic and isomorphic.

Lectotype species: D. gunnianus J. Agardh.

Taxonomic notes: Numerous species have been placed in Dilophus, including 11 from southern coasts of Australia ( Womersley 1967, pp. 211–214). These 11 are here reduced to 7, but as with Dictyota there are few satisfactory species concepts in Dilophus.

J. Agardh (1894a) subdivided Dilophus on whether the margins were thicker than the central part of the branches and on the number of medullary cells centrally in the branch. The presence of thicker margins can be used for species with usually one central medullary layer, but more robust species with 2 or more central layers in young parts lose this character of thicker margins in older parts, and apparently also in rough-water habitats.

References:

AGARDH, J.G. (1882). Till algernes systematik. Acta Univ. lund. 17, 1–136, Plates 1–3.

AGARDH, J.G. (1894a). Analecta Algologica. Cont. I. Acta Univ. lund. 29, 1–144, Plates 1, 2.

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 DILOPHUS

1. Central region of branches with the medulla one or occasionally two cells thick (except in some species near the thallus base), margins 2–4 cells thick	2
1. Central region of branches with the medulla 2–4 cells thick in mid and lower parts, with margins 4–6 cells thick (fewer cells near apices)	6
2. Thallus robust, dark brown, branches 5–15 (–20) mm broad 1	D. robustus
2. Thallus slender to moderately robust, light to medium brown, branches (1–) 2–4 mm broad	3
3. Thallus dichotomous, branched usually at distant intervals, apices broad, with or without surface proliferations	4
3. Thallus becoming alternately branched at frequent intervals, apices of laterals pointed or truncate	5
4. Branches 1–2 mm broad, smooth	D. angustus
4. Branches 2–4 mm broad, undulate	D. marginatus
5. Thallus 8–20 cm high, branches usually 1–3 mm broad, apices of laterals pointed	D. tener
5. Thallus (from type only) 3–6 cm high, branches 2–4 mm broad, with terete to slightly compressed fibres from the truncate branch ends	D. crinitus
6. Thallus dichotomous throughout, branched at intervals of mostly 2–8 cm, branches usually 3–7 mm broad	D. fastigiatus
6. Thallus dichotomous below, often becoming alternately branched above, branched at intervals of 0.5–2 (–4) cm, branches 1–2 (–4) mm broad	D. gunnianus

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