Antonella Bottalico

The prostrate system of the Gelidiales: diagnostic and taxonomic importance

Abstract Despite numerous recent studies on the Gelidiales, most taxa belonging to this order are still difficult to distinguish when in the vegetative or tetrasporic state. This paper describes in detail the morphological and ontogenetic features of the prostrate system of the order with the aim of validating its diagnostic and taxonomic significance. Observations were made on fresh, liquid preserved and cultured thalli. The morphology of the attachment system and the characteristics of rhizoid ontogeny have proven to be useful diagnostic and taxonomic characters. Species belonging to Gelidium, Pterocladia and Pterocladiella bear true attachment organs consisting of cells of both exogenous and endogenous origin. In the family Gelidiellaceae, in contrast, attachment to the substratum is effected by single independent exogenous rhizoids. The attachment rhizoids of the Gelidiales, both exogenous and endogenous, are of the same cell type, and are the so-called hyphae, historically considered typical of the family Gelidiaceae only. A new subdivision of the Gelidiales into three families is proposed here, with the amendment of both Gelidiellaceae and Gelidiaceae, and the Pterocladiaceae fam. nov.

Parviphycus albertanoae sp. nov. (Gelidiales, Rhodophyta) from the Mediterranean Sea

Abstract: Parviphycus albertanoae sp. nov. was described from the southern Adriatic Sea, Italy on the basis of morphological and molecular data. The new species formed dense tufts at the upper intertidal level on rocky substrata, exposed to intense wave action. Distinctive morphological characters were compressed upright axes closely arising from short stolons, numerous first-order branches and clavate tetrasporangial sori at main and lateral apices. Phylogenetic analysis of mitochondrial cox1 and plastid rbcL sequence data revealed that P. albertanoae was clearly separated from the congeners of the genus, corroborating the morphological distinctness.

Growth and reproductive phenology of Pterocladiella capillacea (Rhodophyta: Gelidiales) from the southern Adriatic Sea

Growth, external morphology and reproductive phenology of a southern Adriatic population of Pterocladiella capillacea from a marine cave were investigated. Production of new uprights from creeping axes was limited to late autumn–winter; upright growth in length and branching order increase reached their maxima in late summer. Tetrasporic fronds were dominant from June to September, with a peak in July, while cystocarpic uprights were rather rare and recorded in August only. Two stable, distinct morphotypes occurred in this population at two sampling sites exposed to different daily photon irradiances. Uprights from the more illuminated site were regularly pinnate, with numerous closely packed lateral branches, representing the best-known phenotype of the species; in contrast, uprights from the more shaded inner site had very long and narrow axes, greater intervals between first-order branches and lower branching order. Statistical analysis demonstrated that upright growth in length and branching was significantly different at the two sites; upright biomass in the more illuminated site was generally higher because of the higher orders of branching.

Morphogenesis in Pterocladiella capillacea (Rhodophyta, Gelidiales): bud differentiation in relation to irradiance-temperature combinations

ABSTRACT In Pterocladiella capillacea (Gmelin) Santelices et Hommersand, thallus morphogenesis is controlled by exogenous factors. At 14°C, the adventitious buds arising from the distal pole of frond explants developed into compressed axes, similar to the typical erect shoots of the species, under every irradiance tested. At 19°C and 24°C they developed into compressed axes when irradiance was 20–40 μmol m-2s-1, whereas they developed into terete axes, similar to the typical prostrate thallus, when irradiance was 2.5 to 10 μmol m-2s-1. Buds regenerated from the proximal pole of explants differentiated, as a rule, into terete axes under all conditions, although they may become compressed under the maximum irradiance tested. A hypothesis based on apical dominance is suggested in order to explain the compressed or terete development of the thallus as a response to irradiance and temperature.

Taxonomic revision of Gelidium tsengii and Gelidium honghaiwanense sp. nov. (Gelidiales, Rhodophyta) from China based upon molecular and morphological data analyses

The taxonomic relationship of Chinese Gelidium tsengii and Gelidium johnstonii was ambiguous. For almost 20 years they have been regarded as distinct taxa and until 2002 G. johnstonii was considered as a misapplied name of G. tsengii. In this study, herbarium specimens that initially attributed to G. tsengii and fresh G. tsengii specimens were used to address the taxonomic issues. In phylogenetic studies, G. tsengii from Dayawan, China, near the type locality of G. tsengii and G. johnstonii from Sonora, Mexico, the type locality of G. johnstonii, formed a monophyletic group with maximum support in rbcL and COI genes analyses, indicating that they were genetically identical. In morphological studies, G. tsengii was similar to G. johnstonii in branching pattern, inner structures and fructiferous organs. Consequently, we considered that semi-circular outline of G. tsengii could no longer be treated as a discrimating feature. G. johnstonii had priority of publication and according to the International Code of Botanical Nomenclature, G. tsengii was proposed as a synonym of G. johnstonii. Gelidium honghaiwanense sp. nov. was described from Guangdong, China on the basis of morphological and molecular data. For vegetative structures, it was characterized by flattened upright frond, regular two-three times branches pinnate or alternate and clavate ultimate branchlets. For reproductive structures, the tetrasporangial sori were in the apical part of branches and the tetrasporangial branchlets were distichously distributed along second order branches. The present study clarified the relationship between G. tsengii and G. johnstonii from Guangdong and added a new Gelidium species to the Chinese algal flora.

Developmental stages of attachment of in vitro protoplasts in two Mediterranean Valonia species (Siphonocladales, Chlorophyta)

Abstract In vitro growing protoplasts of two coenocytic green algae, Valonia aegagropila and V. utricularis, developed into small spherules, which behaved as adventitious germlings attached to the substrate. Their developmental patterns are compared, considering that the Mediterranean V. aegagropila is an unattached (pleustophytic) form present in lagoons, whereas V. utricularis is an attached (haptophytic) species of rocky shores. In both species, thin terete branches, able to attach the thallus to the substrate arose from lenticular cells which marked the lower pole of the spherules. Some attachment branches grew as long stolon-like aseptate axes, becoming uniformly green and swelling into secondary vesicular expansions. V. utricularis plantlets usually formed numerous attachment branches, some of which produced other peripheral self-attaching vesicles. On the contrary, V. aegagropila plantlets were fixed by few, weak attachment branches; stolon-like growth was poor and ineffective in extending the attached system. This developmental pattern suggests that, although the Mediterranean V. aegagropila was able to generate attachment branches, these could be easily detached from the substrate by water movement. Therefore, this free floating form typical of lagoons does not originate attached populations as reported for other seas of the world. Some considerations on the taxonomy of Valoniaceae are also made.