The reproductive structures of the Mediterranean alga Laurencia pelagosae (Ceramiales, Rhodophyta)

Eur. J. Phycol. (1993), 28: 141-143.

Printed in Great Britain

I41

The reproductive structures of the Mediterranean alga Laurencia pelagosae (Ceramiales, Rhodophyta)

G. F U R N A R I A N D D. SERIO Istituto e Orto Botanico dell'Universit~, via A. Longo 19, 1-95125 Catania, Italy

Reproductive structures of Laurencia pelagosae are described for the first time. Tetrasporangia, in parallel arrangement, are cut off from the mother cells adaxially; antheridial branches, which are unramified, are inserted in depressions lacking a row of axial cells on their bases; cystocarps are sessile and subspherical. The occurrence of secondary pit-connections between epidermal cells and of lenticular thickenings in the walls of medullary cells is documented. The species is included in the new section Pelagosae within the subgenus Laurencia. Key words: Ceramiales, Laurencia pelagosae, Mediterranean Sea, reproductive structures, Rhodophyta.

Downloaded At: 18:08 24 August 2010

Introduction

Laurencia pelagosae (Schiffner) Ercegovic (Ercegovic, 1949: 66) (basionym: Rodriguezella pelagosae Schiffner, 1931: 149), according to both Schiffner's (1931) and Ercegovic's (1949) descriptions, is characterised by: thallus flat, irregularly and distichously ramified with branches spaced and rare; branchlets short, distichous and opposite, spinelike in the lowest parts of the thallus; both axes and branches, often enlarged, showing a terminal cup provided with trichoblasts; cortical ceils polyhedral. More recently, Cinelli (1979) presented evidence of the occurrence of lenticular thickenings in the walls of the inner medullary cells, and of protein crystals in the cytoplasm of epidermal cells. However, since no descriptions of reproductive morphology have been available, it has not been possible to reassess the taxonomic position of this species, particularly with regard to subgenera and sections of the genus Laurencia which shows complex taxonomic problems (McDermid, 1988). L. pelagosae is an infra-circalittoral species widely distributed in the Mediterranean Sea. All previous records refer to sterile specimens. Female gametophytes have been reported from the eastern coast of Sicily by Cormaci & Furnari (1979) and Cormaci et aI. (1985), but no morphological details were provided. In this paper we present the first report of both tetrasporophytes and male gametophytes observed in specimens collected from Sicily. Materials and methods

Thalli were collected in July and November 1990 by SCUBA at depths of 9 and 14 m at Pozzillo (Catania), epiphytic on Osmundaria volubilis (L.)R. Norris. Herbarium specimens are held at the Botanical Institute of the University of Catania (CAT). All observations were made on fluid-preserved mater-

ial. For microscopic observations, some specimens were stained with 1% aqueous aniline blue acidified with dilute hydrochloric acid which enhances pit-connections. Sections of male specimens, prepared from material dehydrated and embedded in paraffin, were stained with aniline blue. Specimen examined: Rodriguezella pelagosae Schiffner, typus (sterile), Adria, Pelagosa, April 1913. Botanisches Museum Berlin-Dahlem, B19182.

Observations

Vegetative features of our specimens correspond well to those of the type material viz.: thalli red, flat, erect, arising from discoid holdfast, up to 15 cm high; axes 2-3 mm wide, irregularly and distichously ramified; branchlets short, distichous and opposite, spine-like in the lowest parts of the thallus (Fig. 1); cortical cells polyhedral 30-50 /lmX 20-30/~m near the apex and 30-50 #rex 10-15 #m in the median part of the thallus; lenticular thickenings in the walls of the inner medullary cells and secondary pitconnections between epidermal cells (Fig. 2). Tetrasporic thalli bear tetrasporangia in nearly terete stichidial branches, 450-550/~m wide. Tetrasporangia are arranged parallel to the central axis [Saito's (1967) 'parallel type'] (Fig. 3). Sporangia, tetrahedrally divided, are cut off from the mother cells adaxially (Fig. 4). Female gametophytes bear sessile and subspherical cystocarps 450-550 #m wide and 400-500 /~m long, distributed in the middle to subapical part of the thallus (Figs 5, 6). Male plants have spermatangial depressions, deep and ovoid, generally as wide as deep, 280-520 /~mX230-570 #m, located both at the bifurcation of branches and branchlets and laterally near apices (Fig. 7). No row of axial cells occurs on the base of spermatangial depressions (Fig. 8), so depressions are indeterminate.

142

Downloaded At: 18:08 24 August 2010

G. Furnari and D. Serio

Figs 1-9. Laurencia pelagosae. Fig. I. Habit. Fig. 2. Secondary pit-connections between epidermal ceils. Fig. 3. Longitudinal section of stichidial branchlet showing tet-rasporangia in parallel arrangement. Fig. 4. Detail of Fig. 3, showing a young sporangium cut off adaxially (arrow indicates the mother cell). Fig. 5. Female plant with cystocarps. Fig. 6. Detail of cystocarps. Fig. 7. Male plant with spermatangial receptacles. Fig. 8. Longitudinal section of a branchlet showing a spermatangial depression located lateral[y near apex. No row of axial cells occurs on the base of the spermatangial depression. Fig. 9. Unramified antheridial branch ending with an elongate apical cell. Scale bars represent: Figs I and 5, I cm; Figs 3, 4 and 8, 200/2m; Figs 6 and 7, 2 ram; Figs 2 and 9, 100 #m.

143

Reproductive structures of Laurencia pelagosae

Spermatangia are borne on unramified antheridial branches (250-300 /~m long) that terminate in a very elongate apical cell (Fig. 9).

ramis plerumque complanatis, tetrasporangiis adaxialiter ex cellula matricali factis. Type species: L. pelagosae.

Downloaded At: 18:08 24 August 2010

Discussion The occurrence of secondary pit-connections between cortical cells and the parallel arrangement of tetrasporangia in Laurencia pelagosae indicate that this species belongs to the subgenus Laurencia Saito [type species L. obtusa (Hudson) Lamouroux]. Species with compressed thalli in this subgenus are distributed into ~wo sections: Planae Saito et Womersley [type species L. elata (C, Agardh) Hooker et Harvey] and Pinnatifidae J. Agardh [type species L. pinnatifida (Hudson) Lamouroux]. The former section comprises species having abaxial origin of tetrasporangia [L. brongnartii J. Agardh, L, botryoides (Turner) Gaillon, L. distichophylla J. Agardh, L, data (C. Agardh) Hooker et Harvey]; the latter contains species having adaxial origin of tetrasporangia. However, since ~he type species of this last section (L. pinnatifida) does not show secondary pit-connections between cortical cells (Saito, 1982), the section was transferred to the new subgenus Saitoa Furnari et Serio (1993). Therefore, the proposal of a new section within the subgenus Laurencia, characterised b y compressed thalli and adaxial origin of tetrasporangia, seems justified.

Pelagosae sect. nov. Diagnosis. Characteribus subgeneris Laurenciae; thallo et

Acknowledgements W e thank the Curator of the Herbarium of the Botanisches Museum of Berlin-Dahlem (B) for the loan of the Typus of Rodrigueze]]a pelagosae. This work was supported b y a Grant from the Italian M.U.R.S.T.

References CINELLI, F. (1979). Su] valore sistematicodi alcune strutture cellularinel

genere Laurencia(sez.Pinnatifidae),con particolareriferimentoa Laurencia pelagosae(Schiffner)Ercegovic.Inf. Bot. Ita]., 11: 183-186. CORMACL M. & FURNARI,G. (1979). Flora algale della penisola della Maddalena (Siracusa).ThalassiaSalentina,9: 3-18. CORMACI, M., FURNARI,G. & SCAMMACCA,B. (1985). Osservazioni sulle

fitocenosibentonichedel golfodi Augusta(Siracusa).Boll.Acc. GioeniaSci, Nat., 18: 851-87Z. ERCEGOVIC,A. (I949). Sur quelques algues rouges, rares ou nouvelles,de l'Adria~ique.Acta Adriatica, IV(8):3-81. FURNARI, G. & SERIO, D. (1993). The distinc¢ionof Laurencia truncata (Ceramiales, Rhodophyta) in the Mediterranean Sea from Laurencia pinnatifida. Phycologia(in press). MCDERMID,K.J.(1988). Laurencia(Rhodophyfa,Rhodomelaceae):Introduction. In: Taxonomyof EconomicSeaweeds:with Referenceto Some Pacificand Caribbean Species, vol. 2 (Abbott, I.A., edi¢or),231-248. CaliforniaSea Grant CollegeProgram, La Jolla,California. SAIIO,Y. (1982,). Morphology and infragenericposition of three British species of Laurencia(Ceramiales,Rhodophyta).Phyeologia21: 299-306. SCHIFFNER,V. (I93t). Neue und bemerkenswerteMeeresalgen.Hedwfgia,71: 139-205.

(Received 16 November 1992; revised 8 February I993; accepted I March 1993)