This article was downloaded by: [190.0.17.202] On: 24 March 2014, At: 10:46 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK British Phycological Journal Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tejp19 Sexual reproduction in Audouinella arcuata with comments on the Acrochaetiaceae (Rhodophyta) a Gayle I. Hansen & David J. Garbary b a Friday Harbor Laboratories , Friday Harbor, Washington, 98250, USA b Department of Botany , University of British Columbia , Vancouver, British Columbia, V6T 2B1, Canada Published online: 17 Feb 2007. To cite this article: Gayle I. Hansen & David J. Garbary (1984) Sexual reproduction in Audouinella arcuata with comments on the Acrochaetiaceae (Rhodophyta), British Phycological Journal, 19:2, 175-184 To link to this article: http://dx.doi.org/10.1080/00071618400650181 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/termsand-conditions Br. phycol. J. 19:175 184 1 June 1984 Sexual Reproduction in Audouinella arcuata with Comments on the Acrochaetiaceae (Rhodophyta) By GAYLE I. HANSEN Friday Harbor Laboratories, Friday Harbor, Washington 98250, USA and DAVID J. OARBARY Downloaded by [190.0.17.202] at 10:46 24 March 2014 Department of Botany, University of British Columbia, Vancouver, British Columbia V6T2B1, Canada Male, fernale and cystocarpic specimens of Audouinella arcuata (Drew) Garbary, Hansen et Scagel were collected from British Columbia, Canada, and the details of reproductive morphology are described for the first time. The plants consist of one to four branched axes which arc upward from a unicellular base. Each cell contains a single stellate chloroplast with a central pyrenoid. The thalli are mostly bisexual although small plants may bear only male or female gametangia. Spermatangia develop in short, two-celled filaments which are clustered apica[ly on swollen terminal ceils of the main axes. Carpogonia are conical with short bulbous trichogynes and generally terminate short lateral branches. After fertilization a compact monopodial carposporophyte develops which may have up to seven cells in the primary axis and bear up to 25 ovoid carposporangia. Audouinella vaga commonly co-occurs with A. arcuata and is proposed as the possible tetrasporophyte. The reproductive features of A. arcuata are compared to other Audouinella species, and variation in gametangial and carposporophytic morphology is discussed for the family. Numerous investigations on the morphology and taxonomy of the Acrochaetiaceae have been carried out over the past 60 years. Lengthy review articles and monographs on the family have been written by Drew (1928), Papenfuss (1945, 1947), Woelkerling (1971, 1983). Garbary (1979) and Garbary, Hansen & Scagel (1982). The concepts of generic segregation in the family have been debated in the literature as have the diagnostic features of taxonomic value, Most papers point to the problem that few (around 60) of the over 390 species reported for the family have been found to have sexual reproductive structures and, hence, separation of species has had to be based on features of the vegetative plants and of the mono- and tetrasporangia (Woelkerling, 1983). Many different solutions to this problem have been offered. Drew (1928), Dixon & Irvine (1977) and Garbary (1979) simply recognize a single 0007-i617/84/020175 + 10 $03.00/0 10 genus in the family with priority given to the name Audouinella Bory. Woelkerling (1971) goes farther in suggesting that "form genera" be used in the family: Audouinella for those species with known sexual structures and Colaconema for those species in which sex has not yet been reported. A recent proposal of Stegenga & Vromano: (1977) utilizes combinations of life history and vegetative and reproductive features to define genera. Although the latter scheme is attractive, it is difficult to evaluate until the details of life history, and particularly sexual reproduction, are determined for many more species. With the emphasis placed on reproductive development in the systematics of the Florideophyceae, it is of primary importance that these features are revealed in more members of the Acrochaetiaceae, a family considered by some (Chemin, 1937; Garbary, 1978) to be the most primitive in the class. This paper describes the vegetative and, © 1984 British PhycologicalSociety 176 G.I. Hansen and D. J. Garbary for the first time, the complete sexual reproductive morphology of Audouinella arcuata (Drew) Garbary, Hansen et Scagel, a common epiphyte on species of Pterosiphonia and Polysiphonia in the northeast Pacific. Downloaded by [190.0.17.202] at 10:46 24 March 2014 Materials and Methods Sexually reproductive plants of A. arcuata were discovered epiphytic on Pterosiphonia bipinnata (Postels et Ruprecht) Falkenberg from the mid and low intertidal zone in British Columbia, Canada. The two collections of the host bearing these plants were: (1) Vancouver Island, Botanical Beach, (48°32'N, 124°27'W), 13 May 1979; (2) Hope Island, Roller Bay, (50°54'N, 127°57'W), 12 April 1975. Other collections in the herbarium at the University of British Columbia (UBC) were examined but these proved to be sterile or asexual. For microscopic observations, the material was observed fresh or preserved in 5% formalin in seawater. Aniline blue-hydrochloric acid (Papenfuss, 1937) and Wittmann's haematoxylin (Wittman, 1965) were used to stain the preserved preparations. Drawings were made with the aid of a Spencer camera lucida. Observations Habit Plants of A. arcuata occur sporadically on the host, P. bipinnata, with the densest populations often found just below the tips where branching and, hence, surface area is most extensive. The mature epiphytes average 230 jam in height although some plants are found to reach 500 jam. Vegetative morphology The morphology of the epiphytic plants agrees closely with the original description of A. arcuata (as Rhodochorton arcuatum) by Drew (1928). A single subglobose basal cell, 10 14jam in diameter, rests on the outer mucilaginous wall of the host and supports from one to four erect axes (Fig. 1). Each axis develops from a protuberance which extends out from the basal cell before being separated by a cross wall. Axes appear to be initiated from the basal cell at any stage in the development of the plant. They arise straight and erect (perpendicular to the substratum) or laterally and arc upward (hence the specific epithet, arcuata). The cells are barrel to tear-drop shaped, 4-8 jam in diameter and 8-25 jam long, the largest cells occurring near the base of the axes. Each cell contains a single basally eccentric nucleus and a large stellate axile chloroplast with a central pyrenoid. In larger cells, the chloroplast is apical and parietal. Branching is secund or irregular with branches consistently originating from the apex of the supporting axial cell. Reproductive morphology Some of the plants bear terminal chains of monosporangia on the lateral branches (Fig. 4). These occur more frequently on larger plants. The sporangia form in pairs and have the appearance of swollen vegetative cells, 8-10jam wide and 10 jam long. The monospores are released through the apex of the outer sporangial wall, and the empty walls of the chain remain visible. Often the supporting vegetative cell can be seen protruding into the first empty chamber and then appears to be separated by a crosswall, thus regenerating the sporangium. This "regenerative" ability occurs in all types of sporangia produced by the plant. The mature thalli are bisexual with reproductive structures terminal on the axes. Male structures usually form on the main axis which then ceases growth (Figs 2, 4). The apical cell expands in size and cuts off a narrow two-celled filament near its apex. Up to eight of these fertile filaments form successively at the crown of the cell and curve inward slightly, appearing like the fingers on a hand (Fig. 3). The outermost cells in the filaments become spermatangia while the penultimate cells function as spermatangial mother cells, cutting off in an irregular fashion up to three additional spermatangia (2 3 x 3 5 jam). At maturity the male apex resembles the structure of an umbel. Some irregularity does occur. In rare instances the fertile filaments reach three 177 Reproduction in Audouinella go Downloaded by [190.0.17.202] at 10:46 24 March 2014 5 sP"~~~sp mc C$. FIGS 1-9. Reproductive development in Audouinella arcuata: Fig. 1. Sterile plant. Fig. 2. Fertile plant bearing carpogonia (cp), one with a spermatium (s) attached, spermatangia, and young carposporophytes (gon). Fig. 3. Developmental stages of the mature male apex showing the pattern of formation of the spermatangial mother cells (spmc) and spermatangia (sp). Fig. 4. Branch bearing monosporangia (ms)in chains of two and showing empty spore walls (msw) and regenerating monosporangia (rms). Cells have been stippled to show the stellate nature of the chloroplast. Figs 5-9. Developmental stages in the formation of the carposporophyte and the production of terminal carposporangia (csp). Scale = 30 Ixm. Downloaded by [190.0.17.202] at 10:46 24 March 2014 178 G.I. Hansen and D. J. Garbary cells long rather than two with both subterminal cells functioning as spermatangial mother cells. Also, occasionally, both the penultimate and apical cells in an axis may bear fertile filaments. Only one or two cases of each of these situations was observed. The released spermatia are spherical, 3-4pm in diameter, and are covered by a thin layer of mucilage with no obvious ornamentation. The carpogonia are usually terminal on the lateral branches (Fig. 2). Unlike the male axes, the vegetative cell beneath the carpogonium can initiate a new apical cell laterally and continue the growth of the axis. The broadly conical basal portion of the carpogonium resembles a normal vegetative cell except that the chloroplast is not clearly visible. The carpogonial nucleus lies near the basal wall of the cell and a short trichogyne (3-5 ~tm long) develops apically becoming bulbous at its tip. When fertilization occurs, one or two spermatia can be seen attached to the trichogyne and the male nucleus is visible in the carpogonium. After syngamy, the trichogyne withers and is deflected laterally. The base of the carpogonium expands upward and bends obliquely away from the point of trichogyne attachment. The first division of the carpogonium then occurs transversely at the point of bending. Transverse divisions continue to occur apically while all of the cells in the chain initiate lateral branches(Figs 5-9). The mature carposporophyte is monopodial with the main axis containing from four to seven cells (usually five). The shorter lateral branches bear large terminal and lateral ovoid carposporangia (8 x 12 ~tm), and the entire carposporophyte forms a tight cluster of cells up to 60 ~tm in diameter. When carpospores are released, the supporting cell in the filament may expand into the old wall and regenerate the sporangium. Potential tetrasporophyte Attached to the host plant near the gametophytes of A. arcuata are cells which appear to be the released carpospores of our epiphyte (Figs 10, 11). The early germination stages of these spores can be seen and they appear to develop into plants which may be the tetrasphorophytes of A. arcuata. Our observations will be reported here though we are aware that culture studies are necessary to confirm this relationship. When settling on the host plant the spores flatten against the wall and become hemispherical (9-12 x 4-5 gin). The spore divides once internally, becoming septate, and then germinates to form usually two prostrate filaments which penetrate the host wall and grow peridermally within it (Figs 12, 13). At this stage cell walls of endophytic filaments can not be differentiated from cell walls of the host (Figs 13-16). Each cell of the germling contains a single eccentric nucleus and a stellate chloroplast with a central pyrenoid. The filaments grow longitudinally in the middle lamellae of the host pericentral cells. They often branch and traverse the host cells, creating a lattice-like network immediately beneath the surface (Fig. 15). The individual cells of the endophyte vary in size but are usually 3-5 pm in diameter and 5-20 Ilm long. Monosporangia appear to form almost simultaneously from the cells in an endophytic filament by the production of erect, exposed, two- to three-celled filaments which produce ovoid monosporangia (7 x 9-12 gm) terminally and laterally (Figs t4, 15). The endophyte described corresponds to A. vaga (Drew) Garbary, also known to occur on species of Pterosiphonia and Polysiphonia in British Columbia. We have observed rare tetrasporangia in A. vaga. These form on erect filaments up to four cells in length and measure 14-17 gm by 12 14gin (Fig. 16). The sporangia are cruciately divided. Discussion The presence of sexual reproductive structures in A. areuata is rare in natural populations, as indicated by the few known collections. Our discovery of these plants provides the opportunity for us to discuss the importance of sexual features in species Reproduction in AudouineUa ,o 179 ® J 12 13 A @ Downloaded by [190.0.17.202] at 10:46 24 March 2014 ms 14 FIGS 10-16. Stages in the development of the possible tetrasporophyte of A. arcuata: Fig. 10. Newly released carpospores (?). Fig. 11. Settled carpospores showing first cleavage. Fig. 12. Spore germination patterns shown in transverse section. Fig. 13. Young carpospore germtings--surface view. Figs 14, 15. Young tetrasporophytes with monosporangia (ms)--optical section and surface views. Fig. 16. Tetrasporophyte with mature tetrasporangia (tsp). Scale bars = 30 gm. characterization in the family and to consider the relationship of A. arcuata to its congeners. The aspects of sexual reproduction considered here are: (1) unisexuality versus bisexuality, (2) morphology of male gametangia, (3) morphology of female gametangia and (4) postfertilization development. Unisexual versus bisexual plants The unisexual or bisexual nature of spp. has been used as a Audouinella diagnostic feature for separating taxa. In some cases this is a valid criterion: A. densa and A. dasyae are exclusively unisexual (Stegenga & Borsje, 1976; Stegenga & Vroman, 1976), while A. asparagopsis is strictly bisexual (Magne, 1977). However, some species are reported to be variable. B o t h unisexual and bisexual clones are known for A. purpurea (West, 1970). Protogyny has been described in A. simplex (as A. pectinatum) in which female plants produced spermatangia as they grow older (West, 1968). In A. arcuata large plants are 180 G.I. Hansen and D. J. Garbary bisexual while small plants are frequently either male or female. Therefore, we feel that this feature should be used with caution in characterizing species. Downloaded by [190.0.17.202] at 10:46 24 March 2014 Male gametangia Male gametangia in A. arcuata were noted and illustrated by Drew (1928) in the original description of the species, but no details of development or variation were included. We have found that these structures agree with her illustration and that they form in specialized two-celled filaments which develop apically on the modified swollen terminal cell of a vegetative axis. The resulting composite arrangement is "umbellate" in structure and appears to be unique within the genus. Multiple spermatangia have been reported on swollen terminal cells in Kylinia rosulata Stegenga et Van Wissen (Stegenga & Van Wissen, 1979), but in this plant the spermatangia are sessile on the vegetative supporting cell, rather than stalked as in A. arcuata. The occasional occurrence of male branchlets on the penultimate axial cell in A. arcuata does not detract from the fact that the apical cell is still the major part of the terminal "head". Hence these features are diagnostic for A. arcuata. The morphology of spermatangial branches has also been used by Abbott (1962) to characterize species in the Acrochaetiaceae. We find her branching pattern features useful but unfortunately imprecisely defined. She suggests that, in addition to the androphores of Kylinia sensu Rosenvinge (1909), there are four major types of spermatangial branch arrangements for which floral terminology can be used. However, the subtle differences between corymbs and panicles and between panicles and spikes are not distinguished in her paper and have already led to their differing application by other workers. In Table I we have outlined these features as well as others that we feel may be important in taxonomic discrimination. Our list is not exhaustive but tries to cover the range of variation that occurs in the genus with species cited to give examples. Female gametangia The carpogonium in A. arcuata is usually terminal on a single-celled lateral branch, a common feature in the Achrochaetiaceae. Unlike many species, the stalk or supporting cell forms a new apical celt laterally which continues growth of the branch around the fertile cell. This was also noted for A. botryocarpum and three other Audouinella species by Woelkerling (1970, 1971). Within single species of Audouinella, the carpogonia show some morphological variation and are useful in species characterization. The features that we consider taxonomically useful are the location of the carpogonia and the size and shape of the carpogonial base and trichogyne (Table II). Audouinella arcuata is distinguished from many species on the basis of these characteristics alone. The very short, bulbous nature of the trichogyne closely resembles that of A. alariae (Lee & Kurogi, 1983) although in this species the trichogyne is lateral rather than terminal. In a culture study of a plant identified as A. densa f r o m Europe, Stegenga & Vroman (1976) have suggested that the gametophytes of this plant are similar to those of A. arcuata. However, in their material the trichogynes are straight and up to 40 gm long unlike those of A. arcuata which are a maximum of 10 tam long and have a bulbous tip. This feature together with differences in the morphology of the spermatangial branches and in the postfertilization development, indicates to us that the two entities are different. Postfertilization development The carposporophyte of A. arcuata is initiated by a transverse division of the carpogonium and then develops apically to form a monopodial branching system. This transverse initiation is present in virtually all Audouinella spp. except A. yamadae, where Reproduction in A u d o u i n e i l a 181 TABLE I. The range of variation in morphological features related to the spermatangium Feature Location of spermatangia On undifferentiated cells or branches On differentiated mother cells Characteristics Example species (i) Terminal and lateral on branch tips (ii) Lateral on intercalary cell adjacent to carpogonia (i) Androphores A. asparagopsis Reference Magne (1977) (Chemin) Dixon A. alariae Lee & Kurogi (1983) (J6ns.) Woelk. A. rosulata Rosenvinge (1909) (Rosenv.) Dixon (ii) Swollen vegetative cells A. arcuata This paper (Drc~,) Garb. ~l aI. On differentiated accessory branches (i) Forming corymbose clusters A. trichogloeae Abbott (1962) (B6rg.) Garb. (ii) Small "panicles" (or spikes) A. ligorae Abbott (1962) (Bdrg.) Garb. Downloaded by [190.0.17.202] at 10:46 24 March 2014 (iii) Forming umbel-like heads (iv) Lateral "circinnate clusters" A. arcuata A. dotyi This paper Abbott (1962) (Abbott) Garb. Number of spermatangia per mother cell (i) 1 (ii) 1-2 (iii) 1 4 (iv) 4-5 A. subimmersa (Setch. et Gardn.) Garb et Ruen. A. hirsuta (Drew) Garb. et al. ~ arcz~ata A. purpurea Lee & Kurogi (1978) Garbary el al. (1982) This paper West (1969) (Lightf,) Woelk. Shape of spermatangia Size of spermatangia (i) Globose (ii) Ovoid (i) <2 gm (ii) 3 gm A. kurogii Lee et Lindstrom A. arcuata A. dotyi A. simplex (Drew) Garb el al. Lee & Lindstrom (1979) This paper Abbott (1962) West (1968) (as Acrochaetium pectinatum) (iii) 3-5 gm (iv) To 6 gm A. arcuata A. botryocarpa (v) 7 gm A. asparagopsis (Kylin) Hamel This paper Woelkerling (1970) (Harv.) Woelk. the initial division is longitudinal (Abbott, 1966, as Liagorophila endophytica Yamada; Garbary, 1980), and several other species where no division may occur prior to gonimoblast production (see review by Woelkerling, 1983). These deviations from the usual transverse division may have phylogenetic implications, but further studies are needed to determine if the features are more widespread and if they correlate with any other characteristics. Monopodial development of the carposporophyte appears to occur in all species of Audouinella and, therefore, seems to be a generic feature. However, apical growth may not be present in all species. In the drawings Magne (1977) of Abdel Rahman (1980, figs 4, 5) for A. subtilissima and possibly Stegenga & Borsje (1976, fig. 3d, e) for'A, dasyae, the carposporophyte appears to have intercalary growth. This is shown by the deflection of the trichogyne at the point of the first division of the carpogonium and then the attachment of the withered trichogyne two to three cells above the carpogonial base. This feature is unusual in the red algae. If found to be more widespread, it may provide an additional feature for determining species relationships and perhaps for segregating a subgroup from what is traditionally referred to as Acrochaetium. The carposporophyte in A. arcuata is 182 G. I. Hansen and D. J. Garbary TABLE11. The range of variation in morphological features relating to the carpogonium Feature Location of carpogonia Characteristics Example species (i) Terminal on vegetative branches (ii) Lateral and sessile A. arcuata A. yamadae Garb. Reference This paper Abbott (1966), (as Liagorophila endophytica Shape of carpogonial base Length of carpogonial base (iii) (i) (ii) (iii) (i) Lateral and pedicellate Elongate, apically tapering Short conical Ellipsoid 8-12 gm A. A. A. A. A. botryocarpa purpurea arcuata alariae densa (Drew) Garb. (ii) 12-16 gm Chromastrum collopodum (iii) 15-25 p,ln A. subtilissima (iv) 25-35 gm (i) Straight or curved (ii) With basal constriction A. purpurea A. purpurea A, monil~Jbrme (iii) (i) (ii) (i) (ii) (iii) (i) (ii) A. arcuata A. purpurea A. alariae A. arcuata A. subtilissma A, purpurea A. yamadae A. simplex A.floridula (Rosenv.) Papenf. Yamada) Woe!kerling (1970) West (1969) This paper Lee Kurogi (1983) Stegenga & Vroman (1976) Stegenga & Mulder (1979) Abdel Rahman (1980) Downloaded by [190.0.17.202] at 10:46 24 March 2014 (Kfitz.) Garb. Trichogyne shape (Rosenv.) Garb. Trichogyne position Trichogyne length Trichogyne diameter With bulbous tip Apical Lateral 5 10 gm 50-55 gm 100 400 gm 1-1.5 ~tm 2-2.5 gm (iii) 5-7.5 ~tm West (1969) West (1969) Stegenga & Mulder (1979) This paper West (196c~) Lee & Kurogi (1983) This paper Abdel Rahman (1980) West (1969) Abbott (1966) West (1968) Stegenga (1978) (Dillw.) Woelk. a m o n g the largest in A u d o u i n e l l a and contains up to seven cells in the main axis and up to 25 terminal carposporangia. Its developmental pattern and size is very similar to that shown by Woelkerling (1970) for A . b o t r y o c a r p a , although this species differs from A. a r c u a t a in m o s t other features (e.g. chloroplasts, spore germination, basal system). The large c a r p o s p o r o p h y t e contrasts with those described for C h r o m a s t r u m sensu Stegenga & Mulder (1979), a genus to which A. a r c u a t a might be allied on the basis of vegetative criteria alone. However, these authors have defined C h r o m a s t r u m as having small c a r p o s p o r o p h y t e s with a m a x i m u m of 10 carposporangia. This is clearly not the case in A . a r c u a t a . Several aspects of carpos p o r o p h y t e size can easily be quantified to facilitate species comparisons. The features that we consider taxonomically useful are the n u m b e r of cells in the main axis of the c a r p o s p o r o p h y t e , the size of the m a t u r e carposporophyte, and the size of carposporangia (see Table III). Tetrasporoph ytes The patterns of occurrence of g a m e t a n g i a and tetrasporangia in A . a r c u a t a and A. vaga, and the frequent a p p e a r a n c e of these taxa together on or in P t e r o s i p h o n i a lead us to suggest that these entities represent life history phases of the same species. This pattern of a life history with a diminutive g a m e t o p h y t e and a larger tetras p o r o p h y t e is c o m m o n in m e m b e r s of the Acrochaetiaceae with stellate chloroplasts (e.g. Stegenga & Borsje, 1977; Stegenga & Mulder, 1979; Lee & Kurogi, 1983), Another species that might also be the g a m e t o p h y t i c stage of A. a r c u a t a is A. d e n s a (as suggested by West, 1966). However, we feel that this is Reproduction in Audouinella 183 TABLEIII, The range of variation in morphological features relating to the developing carposporophyte Feature Characteristics (i) (ii) (iii) (i) Second to third division main (ii) axis (i) Number of cells in main axis (ii) of carposporophyte (iii) Size of mature carposporophyte (i) (ii) Initial division of carpogonium Downloaded by [190.0.17.202] at 10:46 24 March 2014 Length of carposporangia Transverse Longitudinal Occasionallyabsent Apical Intercalary? 1-2 3 4 4-7 15-25 gm 45-60 gm (iii) 90-100 gm (i) 12 gm (ii) 18-22 ~tm (iii) 24 pm Example species Reference This paper Abbott (1966) Feldmann (1958) This paper Abdel Rahman (1980) Feldmann (1958) Stegenga & Mulder (1979) This paper Stegenga & Vroman (1976) This paper Woelkerling (1970) This paper Lee & Lindstrom (1979) Stegenga & Borsie (1976) A. arcuata A. yamadae A. rosulata A. areuata A. subtilissima A. rosulata A. monilforme A. arcuata A. densa ,4. arcuata A. botryocarpa A. arcuata A. kurogii A. dasyae (Collins) Woelk. less likely since A . d e n s a occurs on a diversity of hosts only one of which is P t e r o s i p h o n i a . In a study of A. d e n s a from Europe, Stegenga & Vroman (1976) report that gametophytic stages were identifiable as A. a r c u a t a . However, on the basis of the morphology of male and female reproductive structures (see discussion above) this is shown to be incorrect. Life history studies starting with field material of both A. a r c u a t a and A. v a g a are needed to resolve this problem, R e l a t i o n s h i p s ofAudouinella arcuata On initiating this study, it was hoped that analysis of the reproductive morphology in A. a r c u a t a would clarify its relationship to other A u d o u i n e l l a species. This has not been the case: A . a r c u a t a shows strong similarities with a diversity of other taxa depending upon which complex of features is considered. In terms of overall development of the carposporophyte, A . a r c u a t a appears to be most similar to A. b o t r y o c a r p a which is vegetatively very different. The spermatangia of A. a r c u a t a are a m o n g the most complex in the family, but resemble K y l i n i a r o s u l a t a s e n s u Stegenga & Van Wissen (1979) in that both species have an apically inflated vegetative cell that bears spermatangia or spermatangial branchlets. These species, however, have trichogynes and chloroplasts that are morphologically different. Since it cannot be determined at present which sets of vegetative and/or reproductive features represent evolutionary convergences, and which represent the true ancestor/ descendant relationships, we consider it best to continue to recognize A u d o u i n e l l a in the broad sense of Dixon & Irvine (1977) and G a r b a r y (1979). If groupings of species are desired, the categories outlined by G a r b a r y (1979) based on vegetative criteria may prove useful. Although the generic problem is still unresolved, the variations in sexual morphology outlined in Tables I, II, and III should provide a more defined basis for taxonomic studies at the specific level. Acknowledgements We would like to thank Professor R. F. Scagel for encouraging the writing of this paper. Gilbert Hughes provided the microscope for the study and Patricia Brammel made helpful suggestions on the drawings. We would like to thank an anonymous reviewer for comments on the manuscript. This research was partly supported by NSERC Grant A-4471 to R.F. Scagel and NSERC Grant V-0014 to D. Garbary. References ABBOTT, I~ A. (1962). Some Liagora-inhabiting species of Aerochaetium. Oec. Pap. Bernice P. Bishop Mus., 23: 77-120. Downloaded by [190.0.17.202] at 10:46 24 March 2014 184 G . I . Hansen and D. J. Garbary ABBOTT, 1. A. (1966). Observations on Liagorophila endophytica, a rare species in the Acrochaetiaceae (Rhodophyta). J. Phycol., 2: 147 150. ABDEL RAHMAN, M. H. M. (1980). 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Phycologia, 22: 59-92. (Accepted 20 December 1983)