Erect Axes Research Articles

SIZE INCREMENTS DUE TO INTERINDIVIDUAL FUSIONS: HOW MUCH AND FOR HOW LONG?1

Size increments following interindividual fusions appear as a general benefit for organisms, such as coalescing seaweeds and modular invertebrates, with the capacity to fuse with conspecifics. Using sporelings of the red algae Gracilaria chilensis C. J. Bird, McLachlan et E. C. Oliveira and Mazzaella laminarioides (Bory) Fredericq, we measured the growth patterns of sporelings built with different numbers of spores, and the magnitude and persistence of the size increments gained by fusions. Then we studied three morphological processes that could help explain the observed growth patterns. Results indicate that in these algae, coalescence is followed by immediate increase in total size of the coalesced individual and that the increment is proportional to the number of individuals fusing. However, the size increments in sporelings of both species do not last >60 d. Increasing reductions of marginal meristematic cells and increasing abundance of necrotic cells in sporelings built with increasing numbers of initial spores are partial explanations for the above growth patterns. Since sporelings formed by many spores differentiate erect axes earlier and in larger quantities than sporelings formed by one or only a few spores, differentiation, emergence, and growth of erect axes appear as a more likely explanation for the slow radial growth of the multisporic sporelings. Erect axis differentiation involves significant morphological and physiological changes and a shift from radial to axial growth. It is concluded that the growth pattern exhibited by these macroalgae after fusion differs from equivalent processes described for other organisms with the capacity to fuse, such as modular invertebrates.

Lomentaria benahoarensis (Lomentariaceae, Rhodophyta), a diminutive epiphytic new species from La Palma, Canary Islands (eastern Atlantic Ocean)

Abstract The marine red alga Lomentaria benahoarensis sp. nov. from the Canary Islands is described. Plants grow epiphytically on Corallina elongata forming turfs of creeping axes attached by lateral discoid holdfasts and erect axes up to 12 mm high. Erect axes are terete to slightly compressed, 200–300(–1000) μm broad, radially branched up to three orders, with laterals progressively thinner, constricted only at the bases of terminal axes. The cortex is three-layered with the outermost cortical cells arranged in a near-continuous surface layer. Medullary filaments form a loose network of narrow elongate cells, which bear secretory cells. Gametophytes are dioecious with spermatangia formed in continuous spermatangial sori; cystocarps are urceolate and ostiolate. Tetrasporangia are subspherical and formed in depressed rounded sori in slightly swollen regions in the middle of fertile terminal axes. The new species has no single unique feature, but differs from the other Lomentaria species by a distinctive combination of attributes. Closest related species to Lomentaria benahoarensis appear to be L. corallicola, L. gracillima, L. monochlamydea, L. orcadensis, L. rawitscheri, and L. tenerrima. Although all these species have a diminutive, decumbent habit and lack regular constrictions in axes, the number of cortical cell layers and the arrangement of outer cortical cells distinguish them.

Laurencia caduciramulosa (Ceramiales, Rhodophyta) from the Canary Islands, Spain: a new record for the eastern Atlantic Ocean

Abstract Laurencia caduciramulosa is recorded for the first time for the eastern Atlantic Ocean off Tenerife, Canary Islands, Spain. The specimens were collected in 2006, growing epilithically in the lower intertidal zone on moderately exposed rocky shores. This species is characterized by reduced size, a well-developed stolon-like basal system and erect axes with abundant deciduous branchlets that function as propagules, except on the uppermost portions of the branches, where they form crowns of branchlets. As in all other reports of this species, gametangia and sporangia were not observed. This study expands the geographical distribution of L. caduciramulosa to the eastern Atlantic Ocean.

Chylocladia wynnei sp. nov. (Champiaceae, Rhodophyta) from the Mediterranean Sea

Abstract A new species, Chylocladia wynnei sp. nov., is described from the Mediterranean Sea. It consists of 2–4 terete, unbranched erect axes, 5–10(–13) mm high, arising from a discoid holdfast. Axes, covered by a thick mucilaginous layer, are hollow throughout. They are divided into segments by monostromatic diaphragms and are constricted at the diaphragms. Axes have a unilayered cortex and longitudinal filaments lining their inner surface; gland cells are cut off from these filaments. Gametophytic plants are dioecious and consist of only two segments. Male thalli have spermatangia in superficial sori located between the two segments. One or two spherical sessile cystocarps are borne on the distal part of the basal segment. Tetrasporic plants comprise 4–5 segments; tetrahedrally divided tetrasporangia are scattered throughout the thallus. These sporangia are transformed from larger cortical cells and, when mature, they protrude into the thallus cavity. Diminutive stature and unbranched erect axes covered with a thick mucilaginous layer clearly distinguish C. wynnei from previously described species of Chylocladia.

The red algal genus Gelidiella (Gelidiales, Rhodophyta) from Taiwan, including Gelidiella fanii sp. nov.

S.-M. Lin and D.W. Freshwater. 2008. The red algal genus Gelidiella (Gelidiales, Rhodophyta) from Taiwan, including Gelidiella fanii sp. nov. Phycologia 47: 168–176. DOI: 10.2216/07-30.1In this study, we document two species of the genus Gelidiella from Taiwan including a new species, Gelidiella fanii sp. nov., from eastern and southern Taiwan. Although the type specimen of Gelidiella acerosa from Yemen was not available during this study, analyses of rbcL sequences indicate that specimens identified as G. acerosa from the Caribbean Sea, southeastern Australia, and the Indo-Pacific oceans and G. fanii from Taiwan are clearly separate species. Gelidiella fanii differs morphologically from Taiwan G. acerosa specimens in having strict unilateral branching, cylindrical to compressed erect axes, numerous surface hairs on the distal ends of branches and branchlets, iridescent thalli, and smaller tetrasporangia.

New and interesting records of Trentepohlia (Trentepohliales, Chlorophyta) from French Guiana, including the description of two new species

F. Rindi and J.M. López-Bautista. 2007. New and interesting records of Trentepohlia (Trentepohliales, Chlorophyta) from French Guiana, including the description of two new species. Phycologia 46: 698–708. DOI: 10.2216/06–88.1Four species of the genus Trentepohlia were collected from French Guiana, including two new to science. Trentepohlia chapmanii sp. nov. formed orange coatings on bamboo reeds and consisted of a thick and compact, pseudoparenchymatous prostrate part on which numerous thin and unbranched erect axes were borne. Trentepohlia infestans sp. nov. produced dark red discolorations on many concrete walls and consisted of crustose masses formed by globular or elliptical cells, from which numerous cylindrical erect axes, supporting sporangiate laterals, arose. Regeneration of sporangiate laterals on the same erect axes was frequently observed. Trentepohlia dusenii, a little-known species, was collected from a metal surface in a forest environment and characterized morphologically. Sporangiate laterals were first observed in this species, and the collection from French Guiana represented its first record for the Americas. Trentepohlia diffracta var. colorata was collected from tree bark in rain forest, representing the second record since the original description from Queensland.

Calcium oxalate crystals in the marine red alga Spyridia filamentosa (Ceramiales; Rhodophyta)

C.M. Pueschel and J.A. West. 2007. Calcium oxalate crystals in the marine red alga Spyridia filamentosa (Ceramiales; Rhodophyta). Phycologia 46: 565–571. DOI: 10.2216/06-101.1Birefringent polyhedral crystals up to 8 µm on a side were found both within cells and on the thallus surfaces of several genetically distinct isolates of the red alga Spyridia filamentosa (Wulfen) Harvey. Diagnostic chemical solubility tests and silver nitrate–dithiooxamide staining identified the crystals as calcium oxalate. Calcium oxalate crystals were observed in all cell types of the vegetative erect axes: axial cells of indeterminate filaments, corticating cells of the main axes, and axial and corticating cells of the determinate lateral filaments (brachyblasts). Thalli cultured in natural seawater medium had few crystals close to the growing apices, whereas older portions of the thalli developed a surface coating of fine crystals and scattered larger extracellular and intracellular crystals. Thalli cultured in natural seawater medium whose calcium concentration was supplemented with 20 mM calcium chloride had an abundance of intracellular and extracellular calcium oxalate crystals. Thalli grown in artificial seawater medium having low calcium concentrations (1.0 and 2.5 mM calcium chloride) deposited few calcium oxalate crystals, but when these thalli were transferred to calcium-rich medium and stressed, crystals formed rapidly. The nonconstitutive nature of calcium oxalate deposition in Spyridia may explain conflicting previous accounts regarding presence of calcium oxalate crystals in this genus.

Two species of Dasya (Ceramiales, Rhodophyta) from Bonin Islands, southern Japan, with the description of Dasya boninensis sp. nov.

SUMMARYTwo species of Dasya in the Dasyaceae (Ceramiales, Rhodophyta) are reported from Bonin Islands, southern Japan. Dasya murrayana Abbott et Millar, new to Japan, is characterized by the following set of features: the tufted habit (up to 30 erect axes developing from a basal disc), small‐sized (6–10 mm high and 350–500 μm in diameter in the middle region), thinly but completely corticated axes, rigid and incurved pseudolaterals forming corymbose heads at the apices of axes and branches, the absence of adventitious monosiphonous filaments, a large number of tetrasporangial stichidia and spermatangial branches per fertile pseudolateral and slender spermatangial branches (35–45 μm in diameter). Dasya boninensis Masuda, Kurihara et Kogame, sp. nov. is characterized by short but thick (10–30 mm high and 600–1000 μm in diameter at the middle portion), heavily corticated axes, indistinct pericentral cells except for the upper portion in transverse sections, soft, straight pseudolaterals and adventitious monosiphonous filaments densely covering the axis and branches, a small number of tetrasporangial stichidia and spermatangial branches per fertile pseudolateral, thick spermatangial branches (65–90 μm in diameter), and short‐necked cystocarps. A dichotomous key to the taxa found in Japanese waters is given.

Sporocladopsis jackii, sp. nov. (Chroolepidaceae, chlorophyta): A new species from eastern Canada and Maine symbiotic with the mud snail, Ilyanassa obsoleta (Gastropoda)

Abstract Sporocladopsis jackii is a new species of green seaweed from eastern Canada and Maine. The species is abundant in late summer and is a conspicuous part of the epizoic flora on living shells of the mud snail, Ilyanassa obsoleta. The alga comprises a densely packed, branched filamentous base from which arise numerous unbranched to sparsely branched erect free axes. Multicellular attenuate hairs are rare to common and terminal on erect axes. Sporangia are clavate, terminal or lateral, usually borne singly, and produced abundantly in summer. Prior floristic accounts from eastern North America may have included S. jackii under the name Pilinia rimosa, now known to refer to a phaeophyte. Pulse amplitude modulation fluorometry of chlorophyll fluorescence (Phyto-PAM) for pigment analysis confirm microscopic observations of the communities living on snails as consisting of primarily Cyanobacteria and Chlorophyta.

Seasonal changes of the introduced Caulerpa racemosa var. cylindracea (Caulerpales, Chlorophyta) at the northwest limit of its Mediterranean range

A study of the meadows of the invasive Caulerpa racemosa var. cylindracea (Sonder) Verlaque, Huisman et Boudouresque was carried out over one year at Marseilles (Provence, France) where the alga is thriving, probably since 1994, in the cold waters of the north western Mediterranean Sea. At an early phase of colonisation, the C. racemosa meadow is characterized by a patchy distribution pattern. Several years are necessary to obtain a dense and continuous meadow. In one area colonized for more than 4 years, C. racemosa has developed a continuous meadow with wide seasonal variations. Maximum development was reached in autumn (biomass: 82 ± 3 g DW m −2; length of stolons: 1162 ± 86 m m −2; number of apices: 8360 ± 405 m −2; number of erect axes: 20955 ± 1499 m −2) and the minimum from winter to early spring (respectively, 0.3 ± 0.1 g DW m −2; 3 ± 1 m m −2; 220 ± 55 apices m −2; 35 ± 15 erect axes m −2). Seasonal variations in the growth rate were highly significant. The season of high growth lasted from June to October. The apical growth rate of a stolon reached a maximum of 7.5 ± 0.3 mm day −1 in early October, then began to decrease significantly from the end of October to December, before becoming nearly nil from January to early May. Annual net production rate expressed in terms of stolon length and biomass was estimated as 5801 m m −2 a −1 and 612 g DW m −2 a −1, respectively. During the growth period, the turnover rate of the C. racemosa stolons was estimated at from 25 to 46 days. The growth rate was closely correlated to the seawater temperature ( R 2 = 0.83), whereas no significant correlation was found between growth and irradiance. During the growth period, a decrease in temperature rapidly affects the growth rate, which soon recovers its earlier level when the temperature rises again. In winter, the growth rate decreased rapidly with the seasonal drop in the seawater temperature. Grazing by fish ( Sarpa salpa and Boops boops) can also affect the growth rate from September to December by consumption of the erect axes and stolon apices, enhancing the ramification of stolons. Seasonal changes at Marseilles are much sharper than those reported for warmer Mediterranean localities (French Riviera, Italy, Croatia): in winter and early spring C. racemosa meadows decreased and locally disappeared, leaving a barren substrate. C. racemosa survives the lower winter seawater temperatures of the north-western Mediterranean Sea probably in the form of zygotes and/or small fragments (rhizoids, stolons, propagules).

Codium fragile: rhizomatous growth in the Zostera thief of eastern Canada

A rhizomatous growth form of Codium fragile is described for the first time. Plants were collected in the Gulf of St. Lawrence in estuaries dominated by Zostera marina. Rhizomatous plants developed from propagules of whole plants that settled horizontally. Horizontal axes of C. fragile were up to 1 m long in plants collected in situ. Plants developed several to dozens of erect axes at right angle to the base. Horizontal growth of up to 0.2 m was found in field experiments where fragments were tied to plastic mesh and left in situ for 4 months. The unconsolidated filaments at the base of C. fragile often wrapped around the rhizomes of Z. marina and up to five separate attachment sites to eelgrass were found in single plants of C. fragile. In four estuaries, 57–100% of Codium plants with identifiable substratum were attached to shoots and rhizomes of Z. marina. The rhizomatous growth form was found in plants identified as C. fragile ssp. tomentosoides (Nova Scotia and Prince Edward Island) and C. fragile ssp. atlanticum (Prince Edward Island), suggesting that this is a phenotypic response to growth in soft bottom environments.

Observations on reproductive morphology and new records of Rhodomelaceae (Rhodophyta) from the Canary Islands, including Veleroa complanata sp. nov.

Polysiphonia funebris and P. tenerrima are examined mainly in relation to their vegetative and reproductive features. In P. funebris the procarps and cystocarps are described for the first time, and it is confirmed that the species exhibits all the vegetative and reproductive features presently used in the delineation of the genus Polysiphonia. The mainly Mediterranean P. tenerrima is reported for the first time in the Atlantic Ocean. This epi-endophyte on Nemalion helminthoides has ecorticate axes with four pericentral cells, abundant trichoblasts spirally ananged, rhizoids cut off from pericentral cells, tetrasporangia produced in spiral series and apparently three-celled carpogonial branches, all diagnostic characters of the genus Neosiphonia. Tetrasporangial plants in the western Atlantic species Dipterosiphonia reversa are described for the first time from a collection that represents the first record of this species in the eastern Atlantic Ocean. Tetrasporangia are produced (one per segment) in short linear series in pinnate laterals, with fertile segments consisting of five pericentral cells; the fertile pericentral cell cuts off two sporangial cover cells. Veleroa complanata Afonso-Carrillo & Rojas-González sp. nov., known only from Tenerife in the Canary Islands, is unique among species of the genus Veleroa because of its progressively corticated polysiphonous axes and its two different types of spirally arranged, determinate, pigmented, persistent trichoblasts. These are unbranched in prostrate and fertile portions of erect axes, but branched, with up to eight alternate-distichous complanate laterals, in vegetative erect axes. A comparative table of the morphological attributes of the species currently accepted in Veleroa is given.

New red alga, Acanthopeltis longiramulosa sp. nov. (Gelidiales, Rhodophyta) from Jeju Island, Korea

SUMMARY A new red alga from Jeju Island, Korea is described. The alga is assigned to Acanthopeltis, Gelidiaceae by the characteristics of terete erect axes, sympodial growth, and suborbicular branchlets that are amplexi-caul at the base. Acanthopeltis longiramulosaY. Lee et Kim is characterized by a discoid holdfast with a few stolons, rhizoids arising from the apex of the branchlet, an erect terete axis diverging into a few branches, longish obpyriform to lanceolate branchlets with smooth surfaces, and tetrasporangial stichidia or sper-matangial and cystocarps appendages on the marginal region of the branchlet. A. longiramulosa is more closely related to Acanthopeltis japonica than Acanthopeltis hirsuta in terms of thallus morphology. However, A. longiramulosa is easily distinguished from A. japonica, which has suborbicular branchlets with setaceous processes on both surfaces.

Contact responses between spores and sporelings of different species, karyological phases and cystocarps of coalescing Rhodophyta

Coalescence is a well documented event in many red algal orders. However, it is as yet unknown if genetic compatibility and phylogenetic relationships could be factors limiting coalescence. Using controlled laboratory experiments complemented with cytological and ultrastructural analysis, in this study we test whether or not coalescence may occur between different seaweed species and between karyological phases of the same species. We also evaluate the effects of one species or karyological phase on the germination rates, germling survival and differentiation of erect axes of sporelings of a second species or phase and whether the uni- or polycystocarpic origin of the coalesced germling may affect the germination and growth or the morphology of the resulting sporeling. Results indicated that the process of coalescence is restricted to intraspecific partners only. A thick interphase with crushed cells and remains of cell walls developed in all the interspecific contacts studied. Results also indicated that coalescence may be expected between individuals of different karyological phases, as in the two cases tested (Mazzaella laminarioides and Sarcothalia crispata) the filaments of both phases grow intertwined in the new tissue of the coalesced crust. Germination rates, sporeling survival and differentiation of erect axes were all affected by the different types of experimental cultures tested. However, results suggest that allorecognition among seaweeds seems to play a minor role in coalescence. The process appears as less sensitive to genetic recognition than the cell fusion processes described for other red algal species or than the colonial fusion described for colonial invertebrates and fungi.

Stirnia prolifera gen. et sp. nov. (Rhodymeniales, Rhodophyta) from the Sultanate of Oman

Stirnia prolifera gen. et sp. nov. is described from the southern region of the Sultanate of Oman on the northern Arabian Sea. This alga forms clumps of erect axes up to 21 cm in height and arising from a well-developed hold-fast system. In Oman it occurs on wave-impacted rocky shores from the lowest intertidal down to a depth of 8 m. It exhibits a distinctive combination of features, including the solid nature of its compressed, dichotomously branched axes and the production of special small fertile proliferations bearing terminal, tetrahedrally divided tetrasporangia in invaginated regions. Male thalli produce the spermatangia also on special small proliferations. Reasons are presented to assign it to the Lomentariaceae (Rhodymeniales).

COALESCENCE VERSUS COMPETITION: FIELD AND LABORATORY STUDIES OF INTRA‐ AND INTERSPECIFIC ENCOUNTERS AMONG COALESCING SEAWEEDS

Classical ecological theory predicts that whenever growing individuals share a common and limiting resource, such as substratum in mid‐intertidal and shallow subtidal habitats, preemptive competition will occur determining species abundance and distribution patterns. However, conspecificity of several ecologically dominant Rhodophyta may coalesce when grown in laboratory cultures. The extent at which intraspecific coalescence occurs in the field and whether the process may also happens during interspecific encounters remain to be determined. If intra‐ and interspecific coalescence effectively occurs, then coexistence through coalescence rises as an alternative to competition among red‐algal dominated intertidal and shallow subtidal communities. Populations of Mazzaella laminarioides and Nothogenia fastigiata living in mid‐intertidal, semi‐exposed rocky habitats in Central Chile are being used to test the above ideas. Intra‐ and interspecific encounters occur in the field throughout the year. Coalescence does occur among conspecific partners but it has not been detected in interspecific encounters. Rather, a thick interface of compressed cells, necrotic tissues and cyanobacterial nodules is formed between the two contacting partners. In addition, observations of laboratory cultures indicate that spore germination, germling survival and differentiation of erect axes in bispecific cultures may be reduced when compared to single‐species controls. Interspecific differences in growth and differentiation rates appear as the mechanisms explaining a lack of coalescence and negative effects during interspecific contacts. On the other hand, the existence of conspecific coalescence in the field suggests this process should be considered as a real alternative to intraspecific competition among coalescing Rhodophyta.

Reinstatement of Grateloupia catenata (Rhodophyta, Halymeniaceae) on the basis of morphology and rbcL sequences

Morphological observations and molecular analysis of a red alga, which has been known as Grateloupia filicina var. lomentaria, G. filicina var. porracea f. lomentaria, or Sinotubimorpha porracea (Cryptonemiales, Halymeniaceae) in the western Pacific, were made for field-collected and cultured plants. The auxiliary-cell ampullae lack tertiary filaments and are of the Grateloupia-type. Morphologically, this alga can be distinguished from G. filicina by (1) the hollow axis; (2) the numerous short proliferations with Lomentaria-like constrictions that densely cover the surface of erect axes in mature plants; and (3) a tendency for reproductive structures to be restricted to the proliferations. The presence of 4.2–4.6% (62–67 bp) nucleotide substitutions in the ribulose-1,5-bisphosphate carboxylase/oxygenase gene (rbcL) between G. filicina and the alga in question also strongly supports the differentiation of these two entities at the species level. The form of the proliferations distinguishes the alga in question from the West Indies G. porracea. Re-examination of type material of Grateloupia catenata Yendo, which has been placed into synonymy under Grateloupia filicina var. porracea f. lomentaria, revealed that our freshly collected specimens matched it, and therefore the Yendo name is reinstated. The topological position of Grateloupia catenata in rbcL trees does not support its separation from other Grateloupia species at the generic rank.

Reappraisal of the type species of Polysiphonia (Rhodomelaceae, Rhodophyta)

The genus Polysiphonia Greville, nom. cons., has had a long and confused nomenclatural history. At present, Polysiphonia has a wide circumscription, including at least 200 species, but it is heterogeneous in many vegetative and reproductive developmental features. Central to any re-evaluation of the genus is a detailed examination of the type species of Polysiphonia, P. urceolata (Lightfoot ex Dillwyn) Greville, which is conspecific with P. stricta (Dillwyn) Greville. We here report on the vegetative and reproductive morphology of P. stricta, including P. urceolata, based on type and other material from the British Isles. Thalli consist of prostrate and erect ecorticate axes with four pericentral cells, attached by unicellular rhizoids remaining in open connection with pericentral cells. Prostrate axes lack vegetative trichoblasts ; trichoblasts occur seasonally on erect axes. Branch initials are cut off from the subapical cell at intervals of four or five segments in dichotomous and alternating pairs rather than being formed from each axial cell in the spiral pattern typical of most species of Polysiphonia. Spermatangial branch initials, which are trichoblast homologues, are produced directly from each axial cell at the tips of erect branches, not subtended by trichoblasts, and have two- to five-celled sterile tips when mature. The mature carpogonial branch is four-celled with a two-celled first sterile group and a one-celled second sterile group. Following presumed fertilization, direct fusion apparently takes place between carpogonium and auxiliary cell; mature cystocarps are usually urceolate. Tetrasporangia are formed from the third pericentral cell, in straight series, and have two pre-sporangial cover cells. Previous accounts of a third, post-sporangial cover cell could not be substantiated. P. stricta and a small group of other Polysiphonia species differ in several important respects from most members of the genus, which have rhizoids cut off from pericentral cells by a cell division, abundant trichoblasts, spirally arranged tetrasporangia and a post-sporangial cover cell. The branching pattern of P. stricta highlights the difficulties of distinguishing between the tribes Polysiphonieae and Pterosiphonieae.

CONVERGENT BIOLOGICAL PROCESSES IN COALESCING RHODOPHYTA

Sporeling coalescence in Gracilaria chilensis Bird, McLachlan et Oliveira produces genetically polymorphic, chimeric individuals. If this is common in red algae, it may have significant biological consequences. In this study, we evaluate the hypotheses that coalescence is widespread among the Rhodophyta and that specific and convergent morphological and ecological responses characterize this as a unique growth style among marine algae. A literature survey on coalescence was undertaken to assess the distribution of this condition in the Florideophycidae. Sixty‐two (54.9%) of 113 species considered germinated to form a disk. Subsequent development in 37 of these species showed crust formation and coalescence during development with other crusts in 31 species (84%). Coalescing red algae were members of the orders Ahnfeltiales, Corallinales, Gigartinales, Gracilariales, Halymeniales, Palmariales, and Rhodymeniales. Ultrastructural studies in species of Ahnfeltiopsis, Chondrus, Gracilaria, Mazzaella, and Sarcothalia suggested a common pattern of early development. Newly released, naked spores may fuse into a single cell, as they do in Chondrus canaliculatus, or they may develop individual cell walls that later are surrounded by a thickened common wall. Ultrastructural studies demonstrated two kinds of immediate development after the first mitotic division: direct development by symmetric divisions resulting in discoid sporelings or an indirect asymmetric arrangement of divisions before a diskoid sporeling was formed. Germination in coalescing species is a linear function of the initial spore density, whereas in noncoalescing species maximum germination occurs at intermediate densities. In the field, coalescing species may recruit either from solitary or aggregated spores. However, survival is significantly higher for plantlets grown from a larger number of coalescing spores. Total number of erect axes formed by the coalesced mass is a logarithmic function of the initial number of spores. Thus, germlings grown from a larger number of coalescing spores exhibited a larger photosynthetic canopy than do plantlets grown from a few spores. Juveniles and mature clumps grown from a coalescing mass may exhibit size inequalities among erect axes, with the larger axes located toward the center of the clump. These larger axes mature first or, in some cases, are the only to produce spores. The widespread occurrence of coalescence inroughly half the number of orders of the Florideophycidae, the similarity of the coalescence process, and the finding of various adaptive traits associated with coalescence characterizes this as a unique growth style, splitting the diversity of species now included in the Florideophycidae into two major groups: coalescing and noncoalescing Rhodophyta.

Polysiphonia perforans sp. nova (Ceramiales, Rhodophyta) from the Mediterranean Sea

ABSTRACT A new species of the genus Polysiphonia from the Mediterranean Sea is described. It is an ecorticate species, with 4 pericentral cells, showing prostrate axes from which erect axes arise. Rhizoids are formed by pericentral cells in a median position remaining in open connection with them. Erect axes are straight, simple throughout or pseudodichotomous at the base then simple or with one (rarely two-three) orders of branching; trichoblasts and scar cells not observed. Only tetrasporangial plants were found. They show ellipsoid tetrasporangia borne in short straight series, often interrupted by sterile segments. The new species is also characterized by a peculiar habit consisting of prostrate axes, adhering to lower faces of Peyssonnelia spp. by means of rhizoids growing upward, from which erect upright axes perforating thalli of the supporting species arise. A comparison with the related species of Polysiphonia was also carried out.