Electronic Flora of South Australia Family Fact Sheet

ORDER CORALLINALES^* Silva & Johansen 1986: 250

Phylum Rhodophyta – Class Florideophyceae

Thallus mostly calcified, growing on rock, plants, animals or other hard substrates, or partly to almost entirely endophytic; partly to completely affixed by cell adhesion, envelopment of host axes or a crustose or rhizoidal holdfast, or growing unattached and free-living as rhodoliths; in geniculate taxa, branches composed of alternating uncalcified genicula and calcified intergenicula. Structure pseudoparenchymatous or more rarely partly to largely composed of unconsolidated filaments; organisation usually dorsiventral and/or radial or isobilateral. Construction in non-geniculate taxa monomerous and/or dimerous or diffuse; monomerous portions consisting of a single system of branched, laterally cohering, filaments that collectively contribute to a ventrally or centrally situated core and a peripheral region where portions of core filaments or their derivatives curve outwards towards the thallus surface; dimerous portions consisting of two distinct groups of laterally cohering filaments or cells: a unistratose ventral or internal layer in which each filament is composed of palisade cells, non-palisade cells or both, and secondly epithallial cells or multicellular filaments arising more or less perpendicularly from cells of the ventral or internal layer of filaments; diffuse portions consisting of branched endophytic or epigenous filaments that are partially or largely non-cohering but usually become partially consolidated in areas of conceptacle production; structure of geniculate taxa usually regarded as multiaxial and differentiated into cortex and medulla; walls of most vegetative cells other than genicula usually impregnated with calcite; cells of adjacent filaments joined by cell-fusions or secondary pit-connections or rarely both, or not interconnected; epithallial cells terminating most filaments at thallus surface, distal walls commonly uncalcified; rhodoplasts discoid and without pyrenoids; pit-plugs with two cap layers including an outer dome-like cap layer. Growth of filaments usually from apical or subapical initials.

Reproduction: Vegetative reproduction by thallus fragmentation, apomeiotic bispores or propagules.

Gametangial thalli monoecious or dioecious; carpogonia and spermatangia produced in separate uniporate conceptacles or rarely in the same conceptacle. Carpogonial filaments mostly 1- to 4-celled, arising from the conceptacle chamber floor or rarely also from the chamber walls. Carposporophytes developing within female conceptacles after karyogamy; carposporangia commonly terminating short gonimoblast filaments that usually arise from a conspicuous or inconspicuous fusion cell, or developing more or less directly from the fertilized carpogonium. Spermatangial filaments unbranched or branched, restricted to the conceptacle chamber floor, or borne on the floor, walls and sometimes the roof.

Tetrasporangia formed within uniporate or multiporate conceptacles or within calcified compartments that may be solitary or more commonly aggregated into sori in non-geniculate taxa; each mature sporangium containing four zonately or (in Sporolithaceae) cruciately arranged spores and in some genera producing apical plugs that individually block a pore of a multiporate conceptacle or a calcified compartment, or collectively block the pore of a uniporate conceptacle prior to spore release; meiotic bisporangia sometimes replacing tetrasporangia; 3-celled sporangia present in Jania minuta.

Life history triphasic with more or less isomorphic gametangial and tetrasporangial generations and a heteromorphic carposporangial generation.

Taxonomic notes: The Corallinales includes two families, both represented in southern Australia. Discussions of characters used to delimit the Corallinales as an order are provided by Silva & Johansen (1986) and Woelkerling (1988, pp. 83–85), and further comments on relationships to other orders are given by Garbary & Gabrielson (1990, pp. 490–491).

The above ordinal circumscription and those for families, subfamilies, and genera reflect current knowledge of these groups. Information on various features, especially relating to reproduction, remain incompletely known or unknown for many species, and as further data become available, modifications to present circumscriptions will become necessary. A comparison of the classification system used here with that used by Woelkerling (1988) testifies to the extent change has been required in the last eight years as a consequence of new research. Similarly, species distribution records for Australia and elsewhere will require updating as new data become available.

Colour may be more or less constant within a species or vary considerably from light to dark pink to purplish, greyish, yellowish, brownish or reddish pink, to red-brown, etc. depending on the interactions of age, habit, light availability, depth of collection, sun-induced bleaching, degree of calcification, and other factors (also note comments of Chamberlain & Keats 1995, p. 138). Senescent or severely stressed specimens sometimes become orangish, greenish or whitish. The colour of partly to largely endophytic species cannot be determined readily. In this account, the colour of many species is described simply as pinkish (sensu Stearn 1983, p. 483); colour is not a reliable diagnostic character for species occurring in southern Australia and cannot be used as a sole basis for identifying specimens.

Notes on the identification of specimens lacking genicula

The calcified nature of the thallus and the occurrence of reproductive structures in conceptacles (or son) readily identifies most members of the Corallinales. Determination to genus and species, however, traditionally has presented formidable problems. Most non-geniculate species cannot be identified from appearance and growth form, and their anatomical features have necessitated the use of specialised terminology.

The internal anatomy of most species can look quite different in different planes of view (Fig. 62B). Except for cell connections, most vegetative features are best seen or can only be seen in sections cut or fractured parallel to the direction of filament growth (i.e. along a group of filaments); such longitudinal views are essential in determining whether the thallus construction is monomerous or dimerous. To determine whether cell-fusions or secondary pit-connections are present, however, it is necessary to examine sections cut or fractured more or less perpendicularly to the direction of filament growth (i.e. across a group of filaments) because such connections occur largely or entirely between cells of different filaments rather than between successive cells of the same filament. When examining conceptacles, it is essential to use sections cut vertically through pore canals and conceptacle chambers; glancing sections through pore canals often show only the peripheral parts of conceptacle chambers and can give a false impression of the structure of reproductive bodies and carposporophytes. Further information on the planes of sectioning is provided by Woelkerling (1988, p. 31).

To facilitate identification of southern Australian specimens lacking genicula, most keys include references to figures showing relevant characters and character states. In addition, a photographic guide to general morphological and anatomical features not explicitly illustrated in the species figures is provided in Figs 62–64. Important characters and character states found in taxa lacking genicula, with references to figures, may be summarised as follows:

GROWTH FORMS: unconsolidated (Fig. 62F, G); encrusting (Figs 69A, B; 80A, 82A); warty (Figs 80B, 88B); lumpy (Fig. 65B); fruticose (Figs 65C, 75A, 88C, 102D, 104D); discoid (Fig. 90A); layered (Figs 86B, 98B, 100B; 108C, D); foliose (Fig. 84B); arborescent (Figs 73A, 113). Woelkerling et al. (1993) provide a detailed account of growth forms in non-

geniculate Corallinales and emphasise that the growth form of many individuals is intermediate between two focal points [e.g. encrusting to fruticose (Fig. 90C), discoid to layered (Fig. 84D), etc.].

BRANCHES: protuberant branch (Figs 62C, 80C, 84C); lamellate branch (Figs 84B, 84D, 98B); ribbon like branch (Fig. 73A); struts (Fig. 78C).

THALLUS ORGANISATION: dorsiventral (Figs 62A–D); radial (Fig. 62E).

THALLUS CONSTRUCTION: monomerous (Fig. 62A, B); dimerous (Fig. 62C, D); diffuse (Fig. 62F, G).

CELLS AND CELL CONNECTIONS: flattened epithallial cells (Fig. 63A); rounded epithallial cells (Fig. 63B); flared epithallial cells (Fig. 63C); palisade cells (Fig. 63D, G); cell fusions (Fig. 63D, F); primary pit-connections (Figs 63E, 63G); secondary pit-connections (Fig. 63E).

RELATIVE LENGTH OF SUBEPITHALLIAL INITIALS: as short as or shorter than the cells immediately subtending them (Fig. 63A); as long as or longer than the cells immediately subtending them (Fig. 63B).

TRICHOCYTES: solitary (Fig. 64A); vertical rows (Fig. 64B); horizontal fields (Fig. 64C); horizontal rows (Fig. 64D).

HAUSTORIA (Fig. 101C).

REPRODUCTIVE STRUCTURES: multiporate conceptacles (Figs 76E, 85A); uniporate conceptacles (Figs 96C, 104E, 114A, B); son (Fig. 65D); calcified compartments (Fig. 66A).

GAMETANGIA AND CARPOSPOROPHYTES: carpogonial filaments (Figs 68B, 91A, 105A, 109A); trichogynes (Figs 68B, 91A, 105A, 109A); unbranched spermatangial filaments (Figs 83D, 101C, 109C, 112B); branched spermatangial filaments (Figs 66D, 91C); carposporophytes (Figs 83C, 96B, 103C, 107C, 112A); conspicuous central fusion cell (Figs 101B, 112A); irregularly shaped fusion cell that looks discontinuous in section (Figs 83C, 91B); gonimoblast filaments (Figs 83C, 103C, 107C, 112A); carposporangia (Figs 83C, 103C, 107C, 112A).

TETRASPORANGIA AND BISPORANGIA: tetrasporangia with apical plugs (Figs 67E, 76D, E, 93A); tetrasporangia without apical plugs (Figs 100D, F, 108E); bisporangia (Fig. 94D); columella (Fig. 100E, F); tetrasporangia with cruciately arranged spores (Fig. 65E); tetrasporangia with zonately arranged spores (Figs 76E, 84E); conceptacles arising at thallus surface from a group of subepithallial initials (Figs 86C, 89A); conceptacles arising adventitiously from a group of vegetative cells within the thallus (Figs 78E, 80E).

Of the 40 or so southern Australian species of Corallinales lacking genicula, 11 or 12 may sometimes be identifiable in the field or with a hand lens or stereomicroscope. The following guide is provided to facilitate preliminary identification; such identifications always require confirmation, however.

GUIDE FOR THE PRELIMINARY IDENTIFICATION OF NON-GENICULATE SPECIES WITH DISTINCTIVE CHARACTERS OBSERVABLE IN THE FIELD OR WITH A HAND LENS

I. Endophytic taxa growing in branches of geniculate corallines

A. Conceptacles of endophyte external on genicula of Metagoniolithon; no evident deformities of host: Lesueuria minderiana (Fig. 101A).

B. Conceptacles of endophyte external on geniculate branches of Haliptilon or Jania; no evident deformities of host: Choreonema thuretii (Fig. 92A, B).

C. Conceptacles of endophyte largely buried within gall like deformities of geniculate branches of Haliptilon: Austrolithon intumescens (Fig. 67A, B).

II. Epigenous taxa with distinctive growth forms

A. Thallus arborescent; tetrasporangial conceptacles multiporate: Mastophoropsis canaliculata (Fig. 73A, B). Caution: male and female/carposporangial conceptacles are uniporate.

B. Thallus arborescent; tetrasporangial conceptacles uniporate: Metamastophora flabellata (Figs 113A, 114C). Male and female/carposporangial conceptacles also are uniporate.

C. Thallus forming small, relatively thin discs affixed at one point to branches of the red algae Ballia or Camontagnea: Synarthrophyton patena (Fig. 90A). Other growth forms of S. patena (Fig. 90B–D) cannot be distinguished from thalli of other species using external features.

D. Thallus forming epilithic plate-like discs commonly 20–150 mm across and 1–3 mm thick that are loosely attached and commonly produce ventral struts: Phymatolithon masonianum (Fig. 78A–C).

E. Thallus producing tightly appressed layers of lamellate branches that look terraced
in surface view and commonly are swirled: Lithophyllum prototypum (Fig. 98B).

Epigenous taxa with distinctive reproductive structures

A. Reproductive structures (tetrasporangia) aggregated into surface sori: Sporolithon durum (Fig. 65D).

B. Multiporate conceptacles composed of a peripheral rim and a central somewhat sunken pore-plate:

1. Thallus forming very thin encrusting thalli, often occurring in large numbers: Melobesia membranacea (Fig. 69A, B).

2. Thallus more massive, encrusting to warty, somewhat lumpy or layered or fruticose: Mesophyllum macroblastum (Figs 86D, 87A); Mesophyllum printzianum (Figs 88D, 89B). These two species cannot be distinguished from one another without anatomical examination of tetrasporangial conceptacle roofs.

* The order description was compiled by W.J.W. with input from H.B.S.W. and H.W.J. The comments which follow on non-geniculate taxa are by W.J.W.

References:

CHAMBERLAIN, Y.M. & KEATS, D.W. (1995). The melobesioid alga Mesophyllum engelhartii (Rhodophyta, Corallinaceae) in South Africa. S. Afr. J. Bot. 61, 134–146.

GARBARY, D.J. & GABRIELSON, P.W. (1990). Taxonomy and evolution. In Cole, K. M. & Sheath, R. G. (Eds), Biology of the red algae, pp. 477–498. (Cambridge University Press: Cambridge.)

SILVA, P.C. & JOHANSEN, H.W. (1986). A reappraisal of the order Corallinales (Rhodophyta). Br. phycol. J. 21, 245–254.

STEARN, W.T. (1983). Botanical Latin. 3 edn. (David & Charles: London.)

WOELKERLING, Wm.J. (1988). The Coralline Red Algae. [British Museum (N.H.): London.]

WOELKERLING, W.J., IRVINE, L.M. & HARVEY, A.S. (1993). Growth-forms in non-geniculate coralline red algae (Corallinales, Rhodophyta). Aust. Syst. Bot. 6, 277–293.

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

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.

KEY TO FAMILIES OF CORALLINALES

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