Electronic Flora of South Australia Family Fact Sheet

Phylum PHAEOPHYTA Pascher

Thallus microscopic to (usually) macroscopic and a few cm to many (to 60) metres long, epilithic or epiphytic (rarely endophytic), or in a few taxa free floating, medium to dark brown with chlorophylls a and c and (3 carotene, masked by xanthophylls (especially fucoxanthin, also violaxanthin and others) contained in phaeoplasts with bands of three thylakoids and with or without a usually stalked pyrenoid, with mannitol and laminarin as the soluble storage carbohydrates. Habit varying from heterotrichous tufts of branched filaments to (more usually) large to massive haplostichous or polystichous thalli, usually much branched in various ways; thalli solid or occasionally hollow, sometimes globose or irregular, or crustose or pulvinate; vesicles (pneumatocysts) present in some larger taxa. Growth diffuse, intercalary, trichothallic or from one or more apical cells; in larger taxa, surface growth is due to a meristoderm. True (phaeophycean) hairs present in many taxa, others with false hairs. Cells uninucleate, with one laminate to several elongate (sometimes branched) or numerous discoid, parietal (central in a few taxa) phaeoplasts*. Physodes usually present, often clustered around the nucleus. Nuclear division phragmoplastic. Cell wall rigid, with an inner layer of cellulose microfibrils and outer more gelatinous layer containing alginic acid; in one genus (Padina) with slight surface calcification.

Reproduction: Reproduction of the sporophyte by zoo(meio)spores from unilocular sporangia (some taxa apomeiotic) or by non-motile tetraspores (Dictyotales); or by zoospores from neutral plurilocular sporangia. Gametophytes isogamous, anisogamous or oogamous with parthenogenesis present in some taxa. Diplontic orders (Fucales and Durvillaeales) oogamous or anisogamous (Notheiales). Plurilocular reproductive organs with a single zooid from each loculus. Motile gametes or sperms with two subapical to lateral flagella, the anterior one longer (except in Fucales) and bearing pinnately arranged hairs (mastigonemes), the posterior flagellum smooth; sperms in Dictyotales uniflagellate, lacking the posterior flagellum.

The Phaeophyta or "brown algae" are almost exclusively marine (some 5 genera are known from fresh waters but not from Australia) and they are usually the conspicuous element of the flora on rocky coasts. Virtually all need a firm attachment and do not grow directly in sand or mud, though small slender forms may grow on small pebbles or shells and a few can thrive on occasion in the free-floating state (e.g. Giffordia mitchelliae and Hormosira banksii). Certain genera (e.g. Macrocystis, Durvillaea) are by far the largest of the marine algae, reaching many metres in length, and many others are between 25 cm and 2 m long. The upper and mid sublittoral zones are usually dominated by brown algae, as described in Part I, Chapter 4 of this "Flora". In contrast to cold temperate Northern Hemisphere coasts where brown algae (e.g. Fucus, Pelvetia) dominate the intertidal zone, only a few (e.g. Splachnidium, Scytothamnus, Scytosiphon, some crustose taxa and Hormosira) grow above low tide level on southern Australian coasts, with a few others emergent during extreme low tides.

The Phaeophyta include some 265 genera and 1500 species, of which 104 genera and 231 species are here recorded from southern Australian coasts (Table 1). Nearly all orders (except the Tilopteridales and the Antarctic Ascoseirales) are present, and most orders are well represented with numerous taxa. Noteworthy orders are the Ectocarpales, Chordariales, Sphacelariales, Dictyotales, Sporochnales and Fucales.

Life history diplohaplontic with isomorphic or heteromorphic generations (in most of the latter group with a larger sporophyte), or direct; or diplontic with meiosis at gametogenesis.

Taxonomic notes: Table 1 gives the distribution of species in the southern Australian region, based on present knowledge; it is likely that further collections will permit the 23 species "restricted" in distribution to be placed in one of the other groups.

The figures in this table differ in some categories from those given previously (e.g. Womersley 1981, 1984). The numbers of genera and species are considerably higher, but the percentage of species endemic to southern Australia is lower at 57%; there are some 21 further species however that occur only in New Zealand, and seven more which occur on subantarctic islands as well. The number and proportion (26%) of species widespread outside southern Australia is considerably higher, but these include some virtually cosmopolitan species (e.g. many Ectocarpales) and others of more limited distribution (e.g. Hormophysa triquetra, Sargassum decurrens).

Within southern Australia, the proportion of species distributed along most of southern Australia is higher at 38%, and the eastern and western elements are both slightly lower; however, more species have been placed in the "restricted" category. The eastern region of southern Australia remains as the richest, with over 80% of the flora known from here.

Several species described below are possible "adventives" which may have been introduced from other coasts of the world. Some have persisted, others apparently not. These species include Sorocarpus micromorus, Elachista orbicularis, Discosporangium mesarthrocarpum, Sphacella subtilissima, Arthrocladia villosa (probably not persistent), Stictyosiphon soriferus, Striaria attenuata, and Asperococcus compressus. Of these, Discosporangium mesarthrocarpum, Sphacella subtilissima and Spermatochnus paradoxus are deep water species from the Mediterranean, as is Zosterocarpus (Z. oedogonium from the Mediterranean, Z. australica from southern Australia). Spermatochnus paradoxus, however, was collected by Harvey at King George Sound, W. Aust., in 1854.

As discussed in Part I, the southern Australian coast varies from cold temperate in Tasmania and Victoria to an intermediate region (to warm temperate) westwards along the rest of the coast. None of this coast can be regarded as distinctively warm temperate. The large cold temperate taxa such as Durvillaea and Macrocvstis characterise Tasmanian and Victorian (to eastern South Australian) coasts, and on the more westward coasts taxa of the Dictyotales and Fucales are prominent. More genera and species of Dictyotales occur on southern Australian coasts than in any tropical region, and in Sargassum the subgenera Phyllotrichia and Arthrophycus are richest in species here but the "tropical" subgenus Sargassum is less well represented.

The classification of the Phaeophyta has been reviewed by several authors in recent years, of whom Scagel (1966), Russell (1973), Wynne & Loiseaux (1976), Bold & Wynne (1978, 1985), Christensen (1980), Wynne (1981) and Clayton (1984) are noteworthy. The classification followed in this "Flora" is close to that of most of the above authors and essentially the same as that of Wynne & Kraft (1981), Wynne (1982) and Bold & Wynne (1985). Recent evidence (see Pedersen 1984) suggests that the Phaeophyta may have evolved from parenchymatous Chrysophyceae.

Most of the orders of Phaeophyta are well established, but this cannot be said for the Chordariales, or for how broad the Ectocarpales should be. A numerical analysis of the British Phaeophyta by Russell & Fletcher (1975) suggested that only 7 orders should be recognised, with a very broad Ectocarpales [including the Ectocarpales (sensu stricto*) and the Chordariales, Dictyosiphonales and Scytosiphonales], and combining the Desmarestiales and Sporochnales. This analysis was based on unweighted characters and so has little relationship to classical classifications where morphological and reproductive characters are weighted to varying degrees. Russell & Fletcher used 132 characters, of which some 116 were based on morphological or reproductive features and the remainder were ecological or habitat features; use of the latter as taxonomic characters was not justified by these authors. Most authors (e.g. Bold & Wynne 1985) have maintained the use of classical weighted characters and recognised as distinct most of the orders combined with others by Russell & Fletcher, though Clayton (1981a) follows the scheme of the latter authors. A rather different arrangement of orders and families is presented by Christensen (1980) in his English version of an earlier book, but unfortunately reasons for his arrangement are not fully given. This arrangement is followed by Pedersen (1984) in a study of brown algae regarded as primitive (Christensen's broad order Tilopteridales including the Dictyosiphonales).

The relationship of orders in the Phaeophyta is well expressed in a diagram by van den Hoek & Jahns (1978) which is given, in modified form, in Fig. 1 here. The closer relationship of the Ectocarpales with the Chordariales and Dictyosiphonales in particular is well shown.

Grouping of the orders into classes or subclasses is also subject to differences of opinion. Most authors recognise a single class, the Phaeophyceae (Fucophyceae** of Christensen 1980), following recognition that the three classes of Kylin (1933) based on life history could not be maintained as the many variations became known. These classes were the Isogeneratae for orders with isomorphic generations, Heterogeneratae for those with heteromorphic generations, and Cyclosporae for the diplontic Fucales. However Scagel (1966) reinstated the subclass Cyclosporidae for the Fucales (including the Durvillaeales) on the basis of different flagellation of the male gametes as well as life history, and Nakamura (1972) recognised two classes (Phaeosporeae and Cyclosporeae) with the Phaeosporeae having three subclasses, viz. the Haplostichidae for entirely filamentous orders, the Haplopolystichidae for orders with both parenchymatous and filamentous stages, and the Polystichidae for entirely parenchymatous orders. These and other classification systems are reviewed by Wynne (1981).

The orders of Phaeophyta are based essentially on their life history, their method of growth and whether the thallus is basically filamentous (haplostichous) or truly parenchymatous (polystichous), their reproduction, and details of cell structure such as the number of phaeoplasts per cell and whether or not a pyrenoid is present (Hori & Ueda 1975). Flagella structure is important in characterising the Fucales and Dictyotales [see review of flagella structure of algae by Moestrup (1982)]. The life histories of brown algae have been reviewed **The 1.C.B.N. does not require that class names should be based on generic names, and there seems little point in not recognising the well established and accepted name Phaeophyceae (and Phaeophyta).

The horizontal line of dashes-polystichous thallus construction above, haplostichous below.

The vertical line of dashes-isomorphic or diplontic life histories to the left, heteromorphic ones to the right.

The slanted line of dashes-diplontic life history to the left, isomorphic to the right.

The inner circle-free filamentous construction within, compacted filaments outside the circle. The middle circle-diffuse growth within, apical or meristem growth outside the circle.

The outer circle-iso or anisogamous reproduction within, oogamous reproduction outside the circle.

The Ralfsiaceae were separated by Nakamura (1972) as a crustose isomorphic order, the Ralfsiales, with a single plate-like phaeoplast without a pyrenoid in each cell, and with a discoid type of germination. However, some members have several phaeoplasts per cell and germination is not always discoid as Fletcher (1978) shows for British taxa and Hollenberg (1969) for taxa on the Californian coast, and the occurrence of isomorphic generations involving a sexual process is not at all well established (Wynne 1981, p. 69). However, the distinctive crustose form, compared to the tufted filaments of the Ectocarpaceae (sensu stricto), gives a ready separation of them and they are placed as a family of the Chordariales in this "Flora". They do, however, superfically resemble the sporophytic crusts of the Scytosiphonales and care is needed in their separation and recognition.

Presence or absence of pyrenoids is in general a valuable character at the ordinal level (Hori 1972; Asensi et al. 1977). Pyrenoids are generally present in primitive orders which are also isogamous or anisogamous but absent in the more advanced oogamous orders. However, pyrenoids present only in reproductive cells or small atypical pyrenoids have occasionally been reported in non-pyrenoid orders.

Few southern Australian taxa have been studied as to their life histories, apart from the detailed contributions of Clayton (1974) on ectocarpoid taxa, Clayton (1976a,b, 1980, 1981 b) on Scytosiphon, Clayton & Ducker (1970) on Punctaria, Skinner (1983; 1985) on Elachista and Skinner & Womersley (1984) on Giraudia. Nearly all other members of the Chordariales, Dictyosiphonales, and to a lesser extent some other orders need such studies.

The separation of haplostichous orders where the thallus is constructed of loosely or compactly aggregated filaments, and polystichous orders where longitudinal as well as transverse cell divisions build up a parenchymatous thallus, is generally recognised. This separation was first proposed by Kuckuck (in Oltmanns 1922, p. 5) and in 1929 (p .6), whose accounts clearly indicated that the differences were recognised as generalities and the longitudinal cell divisions applied to intercalary cells. This was recognised also by Papenfuss (1951, p. 121) and Bold & Wynne (1985, p. 657).

In the heteromorphic polystichous orders, the macrothallus is parenchymatous but the microthallus (whether directly reproducing the sporophytic macrothallus or gametophytic) is largely haplostichous. Kuckuck's distinction of haplostichous and polystichous construction hence applies to the macrothalli of the orders involved.

Difficulties arise in genera where some intercalary cells are longitudinally divided in otherwise uniseriate filaments. In some taxa with prostrate filamentous discs (e.g. flecatonema) this is so, and the position is further complicated in that such genera may be microthallic stages of other genera (e.g. in the Punctariaceae). Pilayella also shows this type of cell division (Russell 1964; Wilce et al. 1982).

The presence of anticlinal divisions in surface (apical) cells of cortical filaments in Scytothamnus and Splachnidium has been regarded as making these genera partly polystichous (Clayton 1985, p. 291). Such divisions occur in other genera where the cortex extends radially (e.g. the Sporochnales, Durvillaeales), but this is distinct from the intercalary longitudinal divisions of truly polystichous taxa (e.g. Scytosiphonales, Dictyosiphonales and Laminariales). Such longitudinal divisions of surface (meristoderm) cells also occur in polystichous orders, and are similar to apical cells which divide in a dichotomous or oblique manner to form two filaments or branches. Hence the Scytothamnaceae and Splachnidiaceae are placed below as families of the haplostichous Chordariales.

Thus haplostichous and polystichous are used here as applying to intercalary cells and as determining the basic thallus structure, accepting that some mainly haplostichous macrothalli may have occasional longitudinal divisions in the otherwise uniseriate filaments.

This Flora expresses the current state of knowledge of southern Australian Phaeophyta. While most of the larger brown algae are now well known taxonomically, the account of most of the orders, and minute taxa in particular, is but a step towards a satisfactory account of the phylum. The key to orders which follows applies to the macrothallus, not in general to the (usually) microscopic microthallus of heteromorphic taxa.

Larger species of the Phaeophyta are of some economic value due to the alginic acid in the cell wall. Those harvested in southern Australia have been the kelp Macrocystis pyrifera on Tasmanian coasts and Durvillaea potatorum ("bull kelp") on King Island in Bass Strait. The amount of Macrocystis available for harvesting proved to be uneconomic, but the Durvillaea is harvested from the drift only, so ensuring the well-being of the in situ Durvillaea zone on the coast. Utilisation of kelps and other algae is reviewed by Levring et al. (1969) and by Waaland (1981).

References:

ASENSI, A.O., DELÉPINE, R. & GUGLIELMI, G. (1977). Nouvelles observations sur l'ultrastructure du plastidome des Phéophycées. Bull. Soc. Phycol. Fr. 22, 192–205.

BOLD, H.C. & WYNNE, M.J. (1978). Introduction to the Algae: Structure and reproduction. (Prentice-Hall: New Jersey.)

BOLD, H.C. & WYNNE, M.J. (1985). Introduction to the Algae: Structure and reproduction. 2nd Edn. (Prentice-Hall: New Jersey.)

CHRISTENSEN, T. (1980). Algae. A taxonomic survey. Fasc. 1 (Tryk: Odense.)

CLAYTON, M.N. & DUCKER, S.C. (1970). The life history of Punctaria latifolia Greville (Phaeophyta) in southern Australia. Aust. J. Bot. 18, 293–300.

CLAYTON, M.N. (1974). Studies on the development, life history and taxonomy of the Ectocarpales (Phaeophyta) in southern Australia. Aust. J. Bot. 22, 743–813.

CLAYTON, M.N. (1976a). The morphology, anatomy and life history of a complanate form of Scytosiphon lomentaria (Scytosiphonales, Phaeophyta) from southern Australia. Mar. Biol. (Berl.) 38, 201–208.

CLAYTON, M.N. (1980). Sexual reproduction-a rare occurrence in the life history of the complanate form of Scytosiphon (Scytosiphonaceae, Phaeophyta) from southern Australia. Br. phycol. J 15, 105–118.

CLAYTON, M.N. (1981a). Phaeophyta. In Clayton, M.N. & King, R.J. (Eds), Marine Botany: an Australasian Perspective, Ch. 5, pp. 104–137. (Longman Cheshire: Melbourne.)

CLAYTON, M.N. (1984). Evolution of the Phaeophyta with particular reference to the Fucales. Progr. Phycol. Res. 3, 11–46.

CLAYTON, M.N. (1985). A critical investigation of the vegetative anatomy, growth and taxonomic affinities of Adenocystis, Scytothamnus and Splachnidium (Phaeophyta). Br. phycol. 1 20, 285–296.

FLETCHER, R.L. (1978). Studies on the family Ralfsiaceae (Phaeophyta) around the British Isles. In Irvine, D.E.G. & Price, J.H. (Eds), Modern approaches to the taxonomy of red and brown algae. Systematics Association Special Volume 10, 371–388. (Academic Press: London.)

HOLLENBERG, G.J. (1969). An account of the Ralfsiaceae (Phaeophyta) of California. J. Phycol. 5, 290–301.

HORI, T. & UEDA, R. (1975). The fine structure of algal chloroplasts and algal phylogeny. In Tokida, J. & Hirose, H., Advance of Phycology in Japan, pp. 11–42. (Junk: The Hague.)

HORI, T. (1972). Survey of pyrenoid distribution in the vegetative cells of brown algae. Proc. 7th Int. Seaweed Symp. Sapporo, Japan. pp. 165–171.

KYLIN, H. (1933). Über die Entwicklungsgeschichte der Phaeophyceen. Acta Univ. lund. N.F. Avd. 2, 29(7), 1–102, Plates 1, 2.

LEVRING, T., HOPPE, H.A. & SCHMID, O.J. (1969). Marine algae: a survey of Research and Utilization. (Cramer, De Gruyter: Hamburg.)

MOESTRUP, Ø. (1982). Flagellar structure in algae: a review, with new observations particularly on the Chrysophyceae, Phaeophyceae (Fucophyceae), Euglenophyceae, and Reckertia. Phycologia 21, 427–528.

NAKAMURA, Y. (1972). A proposal on the classification of the Phaeophyta. In Abbott, I.A. & Kurogi, M. (Eds), Contributions to the systematics of benthic marine algae of the North Pacific, pp. 147–156. (Jap. Soc. Phycol: Kobe.)

OLTMANNS, F. (1922). Morphologie and Biologie der Algen. Vol. 2. (Jena.)

PAPENFUSS, G.F. (1951). Ch. 7. Phaeophyta. In Smith, G.M. (Ed.), Manual of Phycology-an introduction to the Algae and their biology. (Chronica Botanica: Waltham.)

PEDERSEN, P.M. (1984). Studies on primitive brown algae (Fucophyceae). Opera Bot. 74, 1–76.

RUSSELL, G. & FLETCHER, R.L. (1975). A numerical taxonomic study of the British Phaeophyta. J. mar. biol. Ass. U.K. 55, 763–783.

RUSSELL, G. (1964). Systematic position of Pilayella littoralis and status of the order Dictyosiphonales. Br. phycol. Bull. 2, 322–326.

RUSSELL, G. (1973). The Phaeophyta: a synopsis of some recent developments. Océanogr. Mar. Biol. Ann. Rev. 11, 45–88.

SCAGEL, R.F. (1966). The Phaeophyceae in perspective. Océanogr. Mar. Biol. Ann. Rev. 4, 123–194.

SKINNER, S. & WOMERSLEY, H.B.S. (1984). Southern Australian taxa of Giraudiaceae (Dictyosiphonales, Phaeophyta). Phycologia 23, 161–181.

SKINNER, S. (1983). The life-history of Elachista orbicularis (Ohta) comb. nov. (Elachistaceae, Phaeophyta) in southern Australia. Br. phycol. J. 18, 97–104.

SKINNER, S. (1985). Australian and New Zealand species of Elachista and Halothrix (Elachistaceae, Phaeophyta). Trans. R. Soc. S. Aust. 109, 151–160.

VAN DEN HOEK, C. & JAHNS, H.M. (1978). Algen. Einführung in die Phykologie. (Thieme: Stuttgart.)

WAALAND, J.R. (1981). Commercial utilisation. In Lobban, C.S. & Wynne, M.J. (Eds), The Biology of Seaweeds, Ch. 21, pp. 726–741. Bot. Monogr. Vol. 17. (Blackwell: Oxford.)

WILCE, R.T., SCHNEIDER, C.W., QUINLAN, A.V. & vanden BOSCH, K. (1982). The life history and morphology of free-living Pilayella littoralis (L.) Kjellm. (Ectocarpaceae, Ectocarpales) in Nahant Bay, Massachusetts. Phycologia 21, 336–354.

WOMERSLEY, H.B.S. (1981). Biogeography of Australian marine macroalgae. In Clayton, M.N. & King, R.J. (Eds), Marine Botany: an Australasian Perspective, Ch. 11, pp. 292–307. (Longman Cheshire: Melbourne.)

WOMERSLEY, H.B.S. (1984). The marine benthic flora of southern Australia. Part I. (Govt Printer: Adelaide.)

WYNNE, M.J. & KRAFT, G.T. (1981). Appendix. Classification Summary. In Lobban, C.S. & Wynne, M.J. (Eds), The Biology of Seaweeds, pp. 743–750. Bot. Monogr. Vol. 17. (Blackwell: Oxford.)

WYNNE, M.J. & LOISEAUX, S. (1976). Recent advances in life history studies of the Phaeophyta. Phycologia 15, 435–452.

WYNNE, M.J. (1981). Phaeophyta: Morphology and classification. In Lobban, C.S. & Wynne, M.J. (Eds), The Biology of Seaweeds, Ch. 2, pp. 52–85. Bot. Monogr. Vol. 17. (Blackwell: Oxford.)

WYNNE, M.J. (1982). Phaeophyceae. In Parker, S.P. (Ed.), Synopsis and classification of living organisms, Vol. I, pp. 115–125. (McGraw-Hill: New York.)

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 ORDERS OF PHAEOPHYTA

1. Thallus minute to large, internally differentiated or not, haplostichous or polystichous, not reproducing by oogonia and antheridia borne within conceptacles (conceptacles with meiosporangia present in Splachnidium in the Chordariales and with aniso-gametangia in the Notheiales)

2

1. Thallus comparatively large (10 cm to several metres long), morphologically and internally differentiated, polystichous or largely haplostichous, reproducing by oogonia and antheridia borne within conceptacles, either scattered on the thallus branches or in differentiated receptacles

17

2. Thallus tufted, of slender, discrete, filaments of uniseriate, branched, rows of cells

ECTOCARPALES

2. Thallus crustose, prostrate, pulvinate, irregularly lobed, or erect, composed of loosely or densely compacted filaments (haplostichous) or parenchymatous (polystichous), a few to many cells thick

3

3. Thallus a crustose disc or patch, or largely prostrate, becoming several cells thick

4

3. Thallus irregularly pulvinate or globular, or clathrate, or erect and simple or (usually)

8

4. Thallus crustose and basally adherent to substrate, usually without rhizoids

5

4. Thallus prostrate and partly foliose, only partially adherent to substrate and with rhizoids separating thallus from substrate

7

5. Thallus epiphytic, discoid, 0.5–5 mm across, with erect filaments from every cell of central part of disc; cells with several phaeoplasts. family MYRIONEMATACEAE of

CHORDARIALES

5. Thallus epilithic, basal layer bearing erect or assurgent filaments from every cell; cells with one to few phaeoplasts

6

6. Erect filaments straight or assurgent; phaeoplasts usually without a pyrenoid; life history direct (or possibly isomorphic) with unilocular and/or plurilocular sporangia family RALFSIACEAE of

CHORDARIALES

6. Erect filaments straight; phaeoplasts with a pyrenoid; life history heteromorphic, with crusts bearing unilocular sporangia sporophyte of

SCYTOSIPHONALES

7. Thallus only slightly adherent; thallus in cross section with regular rows of cells and a central row of larger cells; sori with large sporangia containing 8 (or 4) spores and without paraphyses genus Lobophora of

DICTYOTALES

7. Thallus moderately adherent; thallus in cross section with larger medullary cells but not a distinct central row; sori with small clavate sporangia producing zoospores

Aglaozonia stage of Cutleria (CUTLERIALES)

8. Thallus developing from one or a row of conspicuous apical cells, producing a terete or flattened, flabellate or much branched thallus

9

8. Thallus without a single or a row of conspicuous apical cells; growth apical by inconspicuous cells, or diffuse, or from or below trichothallic apical hairs

10

9. Thallus branches terete, with a relatively large (when active) apical cell segmenting transversely and then longitudinally (except Sphacella and Discosporangium) below to give distinct tiers of cells; meiospores small, motile

SPHACELARIALES

9. Thallus compressed to flattened, growing from a single apical cell or a row of marginal apical cells, segmenting below and the thallus becoming 2–10 cells thick, usually with an outer small-celled cortex and an inner medulla of relatively clear, similar sized or larger cells; meiospores large, non-motile

DICTYOTALES

10. Thallus growth trichothallic, at the base of prominent single or clustered uniseriate filaments (1–10 mm long) at the apex of each branch or with an apical meristem below tufts of such trichothallic filaments; thallus uniaxial or multiaxial, pseudo-parenchymatous or polystichous

11

10. Thallus growth diffuse or intercalary or apical, usually without apical uniseriate filaments (other than phaeophycean hairs) except in Striariaceae (Dictyosiphonales); thallus multiaxial, with haplostichous axial filaments with terminal and lateral (cortical) branched filaments, or polystichous

13

11. Branch apices each with a single robust filament bearing opposite lateral filaments, becoming corticated below the filament meristem to form a slightly to strongly flattened thallus

DESMARESTIALES

11. Branch apices each with a tuft of filaments, becoming parenchymatous or pseudoparenchymatous and terete to slightly compressed below

12

12. Thallus (gametophyte) slightly compressed; plurilocular gametangia grouped in scattered sori on male or female thalli (sporophyte prostrate, flabellate)

CUTLERIALES

12. Thallus (sporophyte) terete (Carpomitra compressed), with an apical meristem surmounted by a tuft of trichothallic filaments; unilocular sporangia borne laterally on paraphyses densely clustered in sori just below the apical tufts or lower on branches and independent of the apical tufts

SPOROCHNALES

13. Thallus large, usually 25 cm-10 m long and many cells thick, differentiated into a distinct holdfast (usually of haptera), stipe and flat lamina, with an intercalary meristem at the base of the lamina or just below the splitting apex of the frond

LAMINARIALES

13. Thallus a few mm to 50 cm long, pulvinate, convolute, globular, saccate, clathrate, or erect and terete or foliose; not differentiated into a well-defined holdfast, stipe and lamina; growth diffuse, or trichothallic in filaments at the apex of haplostichous branches, or from inconspicuous apical cells

14

14. Thallus epiphytic on Hormosira (rarely on Xiphophora), terete, much-branched mostly from within conceptacles, with a group of 3 inconspicuous, protruding, apical cells; life history diplontic and anisogamous, with conceptacles containing female garnetangia with 8 large motile gametes and male gametangia with 1–4 small, motile gametes

NOTHEIALES

14. Thallus not epiphytic on Hormosira (or if so, then microscopic), without a group of 3 protruding apical cells; conceptacles absent (except in Splachnidium); life history diplohaplontic or direct

15

15. Thallus terete, simple or branched; or compact and globular to pulvinate; or forming small tufts or discs; structure haplostichous, consisting of loosely interwoven filaments bearing sporangia (unilocular or plurilocular neutral) on cortical filaments or in conceptacles; gametophytes microscopic

CHORDARIALES

15. Thallus terete to flattened or foliose, or irregularly globose, convolute or clathrate; structure of macrothallus polystichous (not of loosely interwoven filaments), bearing sporangia or gametangia in or on the cortex

16

16. Cells with several phaeoplasts, with pyrenoids; macrothallus sporophytic

DICTYOSIPHONALES

16. Cells with a single laminate phaeoplast with a large pyrenoid; macrothallus gametophytic

SCYTOSIPHONALES ...

17. Thallus massive (usually 2–12 m long), frond irregularly laciniately divided with a large holdfast (10–40 cm across) and stipe; growth diffuse; oogonia borne laterally on paraphyses or on the wall in conceptacles

DURVILLAEALES

17. Thallus usually 0.3–3 m long, variously branched; growth from 1, a few, or 4 sunken apical cells; oogonia borne on wall of conceptacles

FUCALES


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