A re-evaluation of Scinaia (Nemaliales, Rhodophyta) in the Azores

Abstract

The genus Scinaia in the Azores is re-evaluated based on historical and recent collections. A combination of morphological and anatomical diagnostic characters was used for species segregation, and a key for Azorean species determination is presented. Anatomical information associated to the hair development is described for the first time for the genus. The occurrence of S. furcellata and S. interrupta is confirmed for the archipelago. The presence of S. acuta is reported for the first time in the Azores, representing a spread from Australia to the N-Atlantic and specifically into the Macaronesian region. Its occurrence in the archipelago and the Canaries is discussed as a possible introduction.

Introduction

The genus Scinaia (Nemaliales, Scinaiaceae, Huisman et al. 2004) was established by Bivona-Bernardi (1822) based on Scinaia forcellata, which is now known as S. furcellata (Turner) J. Agardh (for name review see Silva 1992: p. 167 and Silva et al. 1996: p. 114).

Widely distributed around the world (Guiry and Guiry 2009), this genus encompasses 43 species, most of them incompletely described. It has been investigated in NW Europe (Maggs and Guiry 1982), Australia (Huisman 1986, 2006; Millar 1990; Huisman and Womersley 1994), Japan (Kajimura 1988, 1991, 1995), Korea (Lee and Ko 2006) and the Gulf of California (León-Cisneros et al. 2009). These authors described the morphological, anatomical and reproductive features used for species diagnosis. The evolutionary scheme proposed by Huisman (1986) encompassing four groups—‘Scinaia complanata group’, ‘Scinaia moniliformis group’, ‘Scinaia carnosa group’ and ‘Scinaia furcellata group’—was not followed by Kajimura (1995), but he also did not propose an alternative scheme.

Two species of Scinaia have been recorded for the Azores (Neto 1994): Scinaia furcellata, firstly cited for Terceira island by Schmidt (1929), and S. interrupta (A. P. de Candolle) M. J. Wynne, first recorded for the islands of Faial, São Jorge and Pico by Fredericq et al. (1992). The diagnosis of these species was based mainly on external morphological characters, and the genus has not been studied in the Azores since 1994. In the present study, a re-evaluation of the genus in the area is made, based on recent collections, herbarium material and historical collections, including type specimens. A critical re-assessment of vegetative and reproductive features suitable for species determination is made, and an account of the species identified in the area is provided.

Materials and methods

Studied material included fresh collections, historical collections borrowed from AZB and BM, and type material borrowed from BM (herbarium abbreviations as in Holmgren and Holmgren 1998). Fresh specimens were collected intertidally and subtidally (by scuba diving to 30 m depth) during field surveys in the Azores archipelago (Fig. 1) between 2006 and 2008. Samples were fixed in 5% buffered formalin in seawater or pressed following standard protocols and housed at AZB (herbarium of the University of the Azores).

Fig. 1

Collection sites of Scinaia in the Archipelago of the Azores. Graciosa Island: 1 Ponta Branca; 2 Filipe Bay. Pico Island: 3 Madalena channel; 4 Calheta do Nesquim. São Miguel Island: 5 Poços de São Vicente; 6 Porto de Santa Iria; 7 Maia; 8 Feteiras harbour; 9 Moaçor-Ponta Delgada; 10 Pranchinha Bay; 11 Belém Bay; 12 São Roque Islet; 13 Lagoa; 14 Pópulo beach; 15 Viteleiro; 16 Caloura. Santa Maria Island: 17 Restinga; 18 Malbusca

For morphological and anatomical studies, herbarium material was re-hydrated using a saturated detergent solution in warm water. For anatomical examination, semi-permanent microslides were prepared by mounting thin hand-sections of the thallus in 50% corn syrup (Karo Best Foods, Englewood Cliffs, USA), after staining in 1% aniline blue. Measurements of cells and other taxonomically relevant structures were carried out using a calibrated micrometer eyepiece. Photographs were made using a digital camera (Olympus model C5060, Japan) attached to a light microscope (Olympus model BX50F, Japan). Illustration of the specimens’ habit was obtained using a Hewlett-Packard high-resolution scanner. The taxonomic characters commonly used for Scinaia species identification (see Vroom and Abbott 2004; León-Cisneros et al. 2009) were evaluated for the studied material and the more stable and persistent ones were selected for Azorean species segregation, namely, shape and arrangement of utricles in surface view; shape of utricles in transversal view; spermatangium organization; rhizoidal filaments on the cystocarp; and structure of the fusion cell. A dichotomous key to the species from the Azores archipelago was constructed. The systematic arrangement, including the ordinal and lower classification schemes, mainly follows Huisman (2006). The nomenclature used follows Guiry and Guiry (2009).

Results

On the basis of the combination of the selected diagnostic characters and comparison with type specimens and herbaria material, three species of Scinaia were identified for the Azores (Table 1): S. acuta (Figs. 2, 3, 4), S. furcellata (Figs. 5, 6, 7) and S. interrupta (Figs. 8, 9, 10), see key below.

Table 1 Diagnostic characters of Scinaia species from the Azores

Fig. 2

Habitus of Scinaia acuta (SMA-05-191a, AZB)

Fig. 3

Scinaia acuta.a Apical morphology showing abundant small pigmented cells. b Surface view of cortex showing the rosette appearance, displaying large and small polygonal to rounded cells and small pigmented rounded cells (arrowheads) among utricles. c Superficial view of a hair developed near the apex. d Transverse section showing spherical to pear-shaped pigmented cells (PC) and widely obovate utricles (U). e Surface view of spermatangial sorus (arrowheads). f Transverse view of spermatangial sorus showing spermatangial branches (arrowheads) growing among the utricles (U)

Fig. 4

Cystocarp development of Scinaia acuta. a Carpogonial branch showing the basal cell (B) with initial pericarp (arrowhead), the hypogynous cells (H) and the carpogonium (C). b Immature cystocarp showing gonimoblast filaments arising directly from the carpogonium (arrowhead). c Surface view of the hypogynous cell (H) showing the one-celled branch (SF1) and two-celled branch (SF2) sterile filaments surrounded by the pericarp. d–e Developed spherical cystocarp

Fig. 5

Habitus of Scinaia furcellata. a Azorean thallus morphology (SMG-91-10, AZB). Cystocarps scattered along thallus (arrowhead). b Scinaia furcellata type material (BM 000774967)

Fig. 6

Scinaia furcellata.a Apical morphology. b Surface view of cortex near the apical area showing the diffuse rosette appearance, displaying rounded cells interspersed with small pigmented cells (arrowheads). c Surface view of cortex in the middle region showing the rosette appearance with large rounded cells surrounded by smaller angular cells and the small pigmented rounded cells (arrowheads) among utricles. d Transversal view of a hair developed from a small pigmented cell. e Transverse section in the middle region showing medullar filaments (M), spherical to pear-shaped or elongated pigmented cells (PC) and ovoid to obovate utricles (U). f Transverse section of the basal region showing elongated utricles (U). g Surface view of spermatangial sorus (arrowheads). h Transverse view of spermatangial sorus showing spermatangial branches (arrowheads) growing among the utricles (U)

Fig. 7

Cystocarp development of Scinaia furcellata. a Three-celled carpogonial branch. b Carpogonial branch showing the basal cell (B) and the hypogynous cell (H) with initial lateral division and the carpogonium (C). c Surface view of the hypogynous cell (H) showing the one-celled branch (SF1) and two-celled branch (SF2) sterile filaments. d Developed carpogonial branch showing the initial pericarp (arrowhead), the branched hypogynous cell (H) and the carpogonium (C). e Immature cystocarp showing initial gonimoblast (arrowhead) arising directly from the carpogonium (C). f Developing cystocarp showing gonimoblast filaments (arrowhead) and not fused hypogynous branches (arrow). g Fusion cell of mature cystocarp with evident hypogynous branches (arrowheads)

Fig. 8

Habitus of Scinaia interrupta (SMA-05-88, AZB). Cystocarps scattered along thallus (arrowhead)

Fig. 9

Scinaia interrupta.a Apical morphology. b, c Surface view of cortex in the apical area (b) and in the middle region, (c) showing the polygonal appearance and the small pigmented cells (arrowheads) among utricles. d Surface view of the thallus showing the central axis (arrow), radial medullar filaments (M) and abundant hairs (arrowheads). e Transversal view of a hair developed from a small pigmented cell. f Transverse section in the middle region showing pear-shaped to clavate pigmented cells (PC) and oblong utricles (U). g Surface view of spermatangium (arrowhead). h Transverse view of spermatangium (arrowhead)

Fig. 10

Cystocarp development of Scinaia interrupta. a Three-celled carpogonial branch. b Developed carpogonial branch showing the basal cell (B) developing the initial pericarp (arrowhead), the hypogynous cell (H) with the one-celled branch (SF1) and two-celled branch (SF2) sterile filaments and the carpogonium (C). c Mature carpogonial branch showing the trichogyne (arrowhead) attached to the carpogonium (C). d Immature cystocarp surrounded by the multilayered pericarp (arrow) and rhizoidal filaments (arrowheads) growing from basal cell. e Young cystocarp showing gonimoblast (arrowhead) arising directly from the carpogonium (C). f Developing cystocarp showing a fusion cell with hypogynous branches (arrowhead). g Pear-shaped cystocarp showing the fusion cell (arrow), a developed pericarp (P) and rhizoidal filaments (arrowheads). h Cystocarp showing a fusion cell including the lower cells of the gonimoblast filaments (arrowhead). i Spherical mature cystocarp showing rhizoidal filaments (arrowhead)

Key to the species of Scinaia from the Azorean archipelago

 

1a	Utricles in surface view with a polygonal appearance (Fig. 7b, c), cystocarp with rhizoidal filaments (Fig. 10)	S. interrupta
1b	Utricles in surface view with a rosette appearance (Figs. 3b, 6c), cystocarp without rhizoidal filaments (Figs. 4, 7)	2
2a	Utricles in surface view displaying large and small polygonal to rounded cells (Fig. 3b); utricles widely obovate in transverse section (Fig. 3d)	S. acuta
2b.	Utricles in surface view displaying large rounded cells, surrounded by smaller angular cells (Fig. 6c); utricles ovoid to obovate in transverse section (Fig. 6e)	S. furcellata

Species accounts

Scinaia acuta (Setchell) Wynne2005: p. 227 (Figs. 2, 3, 4)

• Basionym: Pseudoscinaia australis Setchell 1914: p. 121, Fig. 62.

• Lectotype: UC 74793 (Setchell 1914: p. 121, Fig. 62).

• Type Locality: Port Phillip Heads near Melbourne, Australia (Setchell 1914: p. 122).

• Vegetative structure: Thalli erect (Fig. 2), soft to firm gelatinous, unconstricted. Axes terete, up to 3 cm in height and 0.5–1.5 mm in diameter, which gradually decrease towards the apical region. Dichotomously branched, up to nine times in two planes, the distance between bifurcations 3–6 mm and relatively constant throughout the whole thallus. Apices acute (Figs. 2, 3a) with a sunken apical pit.

The cortex, initially formed by small coloured cells, later develops into utricles and hypodermal cells, which increase in size towards the older region. In surface view, the utricles have a rosette appearance, displaying large (up to 22 μm) and small polygonal to rounded cells, both thick-walled and colourless (Fig. 3b). Small, pigmented, rounded cells, solitary or in groups of three, occur among utricles. These cells represent vestiges of the hairs commonly found near the apices (Fig. 3c).

The compact central axis, 200–250 μm in diameter, not visible to the naked eye, is formed by thick-walled filaments (5–8 μm wide), giving rise to radial thinner medullary filaments (2–5 μm wide). These support 1–3 layers of pigmented hypodermal cells and an external layer of utricles. In transverse section, the pigmented cells, up to 18 × 8 μm, can be spherical, pear-shaped or elongated. The utricles, widely obovate, measure up to 24 μm in length by 30 μm in width (Fig. 3d).

• Spermatangia: Spermatangia organized in random sori along the thallus surface (Fig. 3e). Spermatangial branches comprise 3–4 cells arising from the hypodermal cells; each mother cell produces 1–3 spermatangia. Utricles are present between spermatangia (Fig. 3f). Thallus is monoecious.

• Carpogonial branch and cystocarp: The carpogonial branch comprises three cells: basal cell, hypogynous cell and carpogonium (Fig. 4a). The basal cell cuts off lateral branches that subsequently grow and produce the pericarp (Fig. 4b). The hypogynous cell produces two sterile branches, one single celled, the other two celled (Fig. 4c). The carpogonium elongates to form the trichogyne. After fertilization, the trichogyne decays and several gonimoblasts arise directly from the carpogonium (Fig. 4b) and develop to produce a compact gonimoblast mass (Fig. 4d, e). As the cystocarp matures, it becomes broadly pyriform to spherical, measuring up to 100 μm in diameter.

• Tetrasporophyte: Unknown.

• Ecological observations: Never abundant, the epilithic gametophytes were found in June in rocky subtidal habitats, at a depth of 14 m.

• Specimens examined: Santa Maria Island: Restinga, 14 m on rocky bottom, coll. N. Álvaro and A. Amaral, 22-Jun-2005 (AZB, SMA-05-191a-b).

Scinaia furcellata (Turner) J. Agardh1851: p. 422 (Figs. 5, 6, 7)

• Basionym: Ulva furcellata Turner 1801: p. 301, pl. I Fig. A.

• Holotype: BM 000774967 (Turner 1801: p. 301, pl. I Fig. A).

• Type Locality: Sheringham, Norfolk, England (Silva et al. 1996).

• Homotypic synonym and references for the Azores: S. furcellata (Turner) Bivona-Bernardi (Schmidt 1929: p. 110; Schmidt 1931: p. 37, 87; Audiffred and Weisscher 1984: p. 27; South and Tittley 1986; Neto 1994: p. 23). S. forcellata (Turner) Bivona-Bernardi (Audiffred and Prud’homme van Reine 1985: p. 47).

• Vegetative structure: Thalli erect (Fig. 5), soft to firm gelatinous, occasionally constricted at the base of the branches (50% of the specimens) more frequently near to the basal area, with some proliferations more common around basal and apical areas. Axes terete, 2–8.5 cm in height and 0.4–4 mm in diameter, which is relatively constant through the whole thallus. Dichotomously branched (occasionally trichotomously) 5–15 times in two planes, the distance between bifurcations increasing towards the apex (1.5–7 (–10) mm in the basal area, 2–14 mm in the apical area). Apices blunt, acute or obtuse (Figs. 5, 6a) with a sunken apical pit.

The cortex, initially formed by small coloured cells, later develops into utricles and hypodermal cells, which increase in size towards the older region. In surface view, the utricles have a rosette appearance, displaying large rounded cells up to 33 μm, surrounded by smaller angular cells, both thick-walled and colourless. The size of the cells gradually increases from the apex to the mid-basal region, making the rosette appearance more evident in this region (Fig. 6b, c). Small pigmented rounded cells, solitary or in pairs, occur among the utricles. These cells represent vestiges of the hairs commonly found near the apices (Fig. 6d).

The compact central axis, (55–) 77–335 (–370) μm in diameter occasionally visible to the naked eye in formol-preserved specimens, is formed by thick-walled filaments (7–20 μm wide), giving rise to radial thinner medullar filaments (2–7 μm wide). These support 1–3 layers of pigmented hypodermal cells and an external layer of utricles. In transverse section, the pigmented cells, up to 22 × 20 μm, can be spherical, pear-shaped or elongated. The utricles, ovoid to obovate (some times elongate in the oldest area), measure 11–33 μm in length by 9–22 μm in width near the apex and 20–48 μm in length by 11–31 μm in width in the mid-basal region (Fig. 6e, f).

• Spermatangia: Spermatangia are organized in random sori along the thallus surface (Fig. 6g). Spermatangial branches comprise 3–4 cells arising from the hypodermal cells; each mother cell produces 1–3 spermatangia. Utricles are present among spermatangia (Fig. 6h). Thallus is monoecious.

• Carpogonial branch and cystocarp: The carpogonial branch comprises three cells: basal cell, hypogynous cell and carpogonium (Fig. 7a). The basal cell cuts off lateral branches that subsequently grow and produce the pericarp (Fig. 7b). The hypogynous cell produces two sterile branches, one single celled, the other two celled (Fig. 7c). The carpogonium (Fig. 7d) elongates to form the trichogyne. After fertilization, the trichogyne decays and several gonimoblasts arise directly from the carpogonium (Fig. 7e), and develop to produce a compact gonimoblast mass (Fig. 7f). A fusion cell is formed by the basal cell, hypogynous cell and fertilized carpogonium; the hypogynous branches, probably with a nutritive function, do not fuse (Fig. 7g). As the cystocarp matures, it becomes broadly pyriform to spherical, measuring 164–249 μm in diameter. Young carpogonial branches and developing cystocarps can be seen scattered along the thallus; mature cystocarps are conspicuous to the naked eye.

• Tetrasporophyte: Filamentous, only known from culture studies (Boillot 1968, 1969; Kornmann and Sahling 1980).

• Ecological observations: Epilithic gametophytes, never abundant, were found from March to July, November and December in tide pools and sandy/rocky subtidal habitats, down to a depth of 17 m.

• Specimens examined: São Miguel Island: Poços de São Vicente, 8 m deep on rocky bottom, coll. unknown, 15-Jul-1997 (AZB, SMG-97-105); Porto de Santa Iria, 10 m deep on rocky-sandy bottom, coll. S. Monteiro and P. Rodríguez, 28-Jun-2001 (AZB, SMG-01-54); Maia, tidal pool, coll. R. Ámen, B. Fletcher, M. Parente, S. Monteiro and A. Neto, 28-May-1998 (SMG-98-328); Feteiras harbour, crevice, coll. R. Ámen, B. Fletcher, M. Parente, S. Monteiro and A. Neto, 28-May-1998 (AZB, SMG-98-593); Moaçor-Ponta Delgada, 8–12 m deep on rocky-sandy bottom, coll. W.F. Farnham and J. Brum, 20-Jul-1994 (AZB, SMG-94–218); Pranchinha Bay, 7–12 m deep on rocky-sandy bottom, coll. J. Azevedo and A. Neto, 07-Jun-1991 (AZB, SMG-91-10); Belém Bay, 17 m deep on rocky-sandy bottom, coll. F. Wallenstein and J. Brum, 12-Jul-1990 (AZB, SMG-90-228); Lagoa, 9 m deep on rocky bottom, coll. J. Azevedo and J. Brum, 20-Mar-1990 (AZB, SMG-90-51); Caloura, tidal pool, coll. M. Parente, R. Ámen and S. Monteiro, 24-Nov-1998 (AZB, SMG-98-1436).

Scinaia interrupta (A. P. de Candolle) M. J. Wynne 1989: 131, Fig. 1 (Figs. 8, 9, 10)

• Basionym: Ulva interrupta A. P. de Candolle 1807: p. 232.

• Holotype: G 20070050/1 (Wynne 1989, Fig. 1; León-Cisneros et al. 2009, Fig. 16).

• Type Locality: Rade de Brest, Brittany, France (Athanasiadis 1996: p. 34).

• Heterotypic synonym and references for the Azores: Scinaia turgida Chemin 1926: p. 102, Figs. 2, 3 (Fredericq et al. 1992: p. 2; Neto 1994: p. 24; Tittley and Neto 1994: p. 11).

• Vegetative structure: Thalli erect (Fig. 8), soft gelatinous, with occasional proliferations and constrictions at the base of the branches (seen in 13% of the specimens). Axes terete to ellipsoidal, 1.5–10 cm in height and 0.9–4 mm in diameter, which is relatively constant through the whole thallus. Dichotomously branched 4–14 times in two planes, the distance between bifurcations increases towards the apex (1–8 mm in the basal area, 2–14 mm in the apical area). Apices acute or obtuse (Figs. 8, 9a) with a sunken apical pit.

The cortex, initially formed by small and coloured cells, later develops into utricles and hypodermal cells, which increase in size towards the older region. In surface view, the utricles are polygonal in appearance (Fig. 9b, c), displaying tetra-octagonal (some rounded) colourless and thin-walled cells 11–44 μm in diameter. The size of the cells gradually increases from the apex to the mid-basal region. Small pigmented rounded cells, solitary or in groups of three, occur among utricles (Fig. 9c). These cells represent vestiges of the hairs commonly found near the apices (Fig. 9d, e).

The compact central axis (Fig. 9d) up to 376 μm in diameter, visible to the naked eye on formol-preserved and fresh material, is formed by thick filaments (7–13 μm wide) surrounded by thick walls, giving rise to radial thinner medullary filaments (2–7 μm wide). These support 1–3 layers of pigmented hypodermal cells and an external layer of utricles. In transverse section, the pigmented cells, up to 15 × 35 μm, can be pear-shaped to clavate. The utricles, squared to oblong, measure 20–31 μm in length by 11–26 μm in width near the apex and 24–44 μm in length by 17–35 μm in width on the mid-basal region (Fig. 9f).

• Spermatangia: Spermatangia scattered along the thallus surface, mainly in the younger parts, without forming sori (Fig. 9g). Spermatangial branches comprise 3–4 cells arising from the hypodermal cells; each mother cell produces several spermatangia (Fig. 9h). Thalli are monoecious.

• Carpogonial branch and cystocarp: The carpogonial branch, formed near the apices of the thallus, comprises three cells: basal cell, hypogynous cell and carpogonium (Fig. 10a). The basal cell cuts off lateral branches, which eventually will form the pericarp and the rhizoidal filaments (Fig. 10b, d). These later are located at the base of the cystocarp and resemble a root system (Fig. 10d, i). The hypogynous cell produces two sterile branches, one single celled, the other two celled. The carpogonium elongates to form the trichogyne (Fig. 10c). After fertilization, the trichogyne decays and several gonimoblasts arise directly from the carpogonium (Fig. 10e) and develop to produce a compact gonimoblast mass surrounded by an elongate pericarp (Fig. 10f, g). A fusion cell is formed by the basal cell, hypogynous cell, fertilized carpogonium, the hypogynous branches and ultimately the lower cells of the gonimoblast filaments (Fig. 10f, h). As the cystocarp matures, it becomes pear-shaped to spherical (Fig. 10i), measuring 175–271 mm in diameter and being conspicuous to the naked eye. Older cystocarps occur in the basal region of the thallus.

• Tetrasporophyte: Filamentous, only known from culture studies (Boillot 1971; León-Cisneros et al. pers. obs.).

• Ecological observations: Gametophytes, never abundant, were found growing epilithically in sandy/rocky subtidal habitats at depths of 5–30 m, from of May to July.

• Specimens examined: Graciosa Island: Ponta Branca, 30 m deep on sandy bottom, coll. N. Álvaro, A. Amaral and D. Torrão, 02-Jul-2006 (AZB, GRW-06-510a-i). Pico Island: Madalena channel, 30 m deep on sandy-rocky bottom, coll. D. Villegas, R. Coma and N. Álvaro, 24-Jul-2007 (AZB, PIX-07-1203a). São Miguel Island: Porto de Santa Iria, 12 m deep on rocky-sandy bottom, coll. K. León-Cisneros and A. Amaral, 17-Jun-2008 (AZB, SMG-08-14); Moaçor-Ponta Delgada, 15 m deep on rocky-sandy bottom, coll. J. Brum, 24-Jun-1999 (AZB, SMG-99-849); Pranchinha Bay, 7–12 m deep on rocky-sandy bottom, coll. J. Azevedo and A. Neto, 07-Jun-1991 (AZB, SMG-91-09); Belém Bay, 17 m deep on rocky-sandy bottom, coll. F. Wallenstein and J. Brum, 12-Jul-1990 (AZB, SMG-90-229); Lagoa, 14 m deep on rocky-sandy bottom, coll. W.F. Farnham and A. Neto, 25-Jul-1996 (AZB, SMG-96-363). Santa Maria Island: Malbusca, 20 m deep on rocky-sandy bottom, coll. F. Wallenstein, 07-Jun-2005 (AZB, SMA-05-88).

Discussion

Scinaia acuta is reported for the first time in the Azores, and the occurrence of S. furcellata and S. interrupta in this region is confirmed. Anatomical observations regarding hair development are described here for the first time for this genus. Pigmented cells previously reported as monosporangia (Svedelius 1915; Maggs and Guiry 1982; Huisman 1985, 1986; Kajimura 1988, 1991, 1995; Afaq-Husain and Shameel 2001) or initial spermatangia (Krishnamurthy and Sundararajan 1987) were found to represent the hairs initial development (Figs. 3a–c, 6b–d, 9d–e). Further studies involving other species of the genus are needed to validate this taxonomic character for genus segregation. The anatomical structure of the fusion cell (Fig. 10f–h) is reported for the first time for S. interrupta.

Following the classification scheme of Huisman (1986), two morphological groups can be found in the Azores: (1) “S. furcellata group”, represented by S. acuta and S. furcellata, characterized by thalli with utricles organized in a rosette superficial pattern, and (2) “S. carnosa group”, represented by S. interrupta, encompassing non-flattened plants not always regularly constricted, with utricles organized in a polygonal superficial pattern. No members of the “S. complanata group” and “S. moniliformis group” were found in the Azores. The limits between these morphological groups are, however, unclear (see León-Cisneros et al. 2009). Moreover, as previously discussed by the latter authors, the three species in the Azores show the same reproductive pattern where the hypogynous cells produce two lateral sterile branches (one celled, two celled), a feature that according to Kajimura (1995) should place them into one single group. Scinaia species occurring in the Azores are anatomically distinct and easily separated by microscopic examination of the thallus surface cells, even if only small fragments or incompletely re-hydrated specimens are observed. Morphologically, however, they are very similar and exhibit mainly cylindrical and not regularly constricted thalli. A combination of morphological and anatomical features was used in the present study, which proved to be efficient in species segregation and is recommended for further studies.

Azorean plants of Scinaia acuta correspond to the morphological original description of Setchell (1914: p. 121, Fig. 62) for Australian material and the descriptions and illustrations of Huisman (1986: p. 284, Figs. 48–51) and Reyes et al. (1993: p. 55, Figs. 23–24) for plants from Australia and the Canaries, respectively.

In general, Azorean Scinaia furcellata correspond to the morphological original description of Turner (1801: p. 301, pl. I fig. A) for material from England and the descriptions and illustrations of Bivona-Bernardi (1822: p. 232, Figs. A–C), Setchell (1914: p. 91, pls 10, 14), Joly (1965: p. 115, Fig. 241), Dixon and Irvine (1977: p. 145, Figs. 54a, b), Maggs and Guiry (1982: p. 520, Figs. 1, 7, 8), and Huisman (1985: p. 405, Figs. 2–9, 10–16) for plants from Italy, Brazil and NE Europe, respectively.

Azorean plants of Scinaia interrupta correspond to the morphological original description of Candolle (1807: p. 232) for material from France, the descriptions and illustrations of the holotype by Wynne (1989: p. 131, Fig. 1) and León-Cisneros et al. (2009: p. 199, Fig. 16) and the descriptions and illustrations of Maggs and Guiry (1982: p. 520, Figs. 2–4, 11) and León-Cisneros et al. (2009: p. 195, Figs. 15–27) for plants from NE Europe and Gulf of California, respectively.

Scinaia furcellata and S. interrupta, previously recorded for the Azores (Neto 1994) fall within their overall distributional range. The former was firstly described for England and later referred to many other locations, being widely distributed around the world (Guiry and Guiry 2009). The latter, described for France and for long only known for the Atlantic (Guiry and Guiry 2009), was recently reported to occur in the Gulf of California (León-Cisneros et al. 2009) and is likely to have a wider distribution.

Scinaia acuta was originally described for Australia (Setchell 1914), later for the Canaries (Reyes et al. 1993) and now for the Azores, a distribution pattern that suggests its introduction to these Macaronesian archipelagos. There are twelve species of marine algae classified as non-indigenous species for the Azores (Cardigos et al. 2006). Little is known on marine species introductions and invasions to this archipelago, but its high potential for introductions has been widely discussed, considering the increase of the transatlantic leisure boat-traffic stopping at these islands. S. acuta, like Asparagopsis armata Harvey, a well-known invasive species in the Azores, has its origin in the southern hemisphere. Its presence in the Azores suggests a northward expansion of its distribution area in the Atlantic,

Further research involving long-term studies of the qualitative and quantitative evolution of the littoral algal flora analysed in the light of the biogeographic affinities and ecological requirements (tropical, sub-tropical and warm temperate) would help to evaluate and understand the expansion patterns of these marine macroalgae, preferably complemented with physiological studies on their responses to environmental stresses.