First report of the melobesioid alga (Corallinales, Rhodophyta) Mesophyllum incisum (Foslie) Adey in South Africa
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Abstract:
Mesophyllum incisum is reported and studied for the first time in South Africa. It has a thallus surface (SEM) with Leptophytum-type epithallial cells. Tetra/bisparangial conceptacles are mound-like and lack a peripheral rim but have a flattened pore plate. The rosette cells surrounding the tetrasporangial pores are distinct from surrounding roof cells (SEM, surface view) in being narrower, and sunken below the level of the surrounding pore plate. The cells of filaments bordering the tetrasporangial conceptacle pore canal differ from the other roof cells within the pore plate in being more elongate, narrower, and often more densely staining. Pore canal filaments also generally contain fewer cells than the surrounding filaments of the pore plate and the pore canal is more-or-less parallel sided. Our material agrees closely with the species as reported in Australia.Keywords:
Thallus
Rosette (schizont appearance)
The plants of Dictyopteris australis (Sonder) Askensay are large, ribbon-like, dichotomously branched with a distinct midrib : The wing portion of the thallus is 2 or 3 celled thick and midrib is about 5 celled thick. The deflexed lines of hairs borne on both surfaces of the thallus show tetrasporangia at various stages of development. Tetrasporangia are partially embeddded and possess at maturity, a three layered wall with varying amounts of alginic acid and sulphated polysaccharides. The tetrasporangial cytoplasm shows abundant physodes, sulphated polysaccharides and vacuoles of various shapes and sizes. A reduction division results in the formation of tetraspores which are released by a highly coordinated mechanism. The outer layer of the tetrasporangium ruptures and the middle layer forms a stalk, temporarily holding the released tetraspore mass to the parent thallus. The tetraspores which are initially enclosed in middle and inner layer are later set free. The older thalli also show the formation of vegetative plants that remain attached to the parent thallus by means of branched rhizoids.
Thallus
Stalk
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Five species of red algae were recorded for the first time in Korea: Acrochaetium plumosum (Drew) Smith, Gelidium australe J. Agardh, Gelidium galapagense Taylor, Cryptonemia lactuca (c. Agardh) J. Agardh, and Kallymenia harveyana J. Agardh. Their habitats and morphological characters were described with illustrative figures. Acrochaetium plumosum is characterized by obovoid to clavate cells with thick walls, stellate chloroplasts with a central pyrenoid, mono sporangia that are produced singly or in a: concatenate form of two, and branching secundly and distichously. Gelidium australe is characterized by terete and slightly compressed axes and branches, terete and slightly contorted branchlets, and spatulate to lanceolate forms of tetrasporangial stichidia. Gelidium galapagense is characterized by a thallus composed of stolons and erect foliaceous branches with short digitate branchlets, and palmate forms of tetrasporangial stichidia. Cryptonemia lactuca is characterized by flabellate, subcartilagineous, strongly undulate, di-polychotomously laciniate thalli, with a midrib in the lower portion of the thallus, and tetrasporangia in the cortical layer of the small segments formed on the apical margin of the blade. Kallymenia harveyana is characterized by the gelatinoid and laminate thallus with a very short stipe, with the cortical cells compacted with small granules, and stellate cells in the medulla.
Thallus
Pyrenoid
Ulva lactuca
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The Acrotylaceae is composed of Acrotylus australis J. Ag., Hennedya crispa Harv., Amphiplexia hymenocladioides J. Ag. and A. racemosa (J. Ag.) comb, nov. (all endemic to southern Australia), Reinboldia polyearpa Schmitz from South Africa and Ranavalona duckerae gen. et sp. nov. from southern Madagascar. The species are multiaxial, zonately tetrasporangiate and monoecious. In Acrotylus and Ranavalona the tetrasporangia develop in raised nemathecia, whereas they are scattered in the other species. In Amphiplexia hymenocladioides, tetrasporangia are intercalary in contrast to the other species with known tetrasporophytes. Acrotylus and Ranavalona are polycarpogonial, with the carpogonial branches of Ranavalona being additionally nemathecial. The remaining genera are monocarpogonial, with scattered carpogonial branches. The carpogonia in all species are directed laterally or thallus-inwardly and provided with reflexed trichogynes. The species are all procarpic (except possibly Reinboldia), with supporting cells of carpogonial branches functioning as auxiliary cells. Fusion cells do not form, and several gonimoblast initials arise directly from diploidized auxiliary cells and enter an adjacent region of 'nutritive' cells. Gonimoblast development is thallus-outward in Amphiplexia and thallus-inward in Acrotylus, Ranavalona, Hennedya and possibly Reinboldia, the last genus being known only from a surviving fragment of the type specimen. In all but Amphiplexia, breakdown of the auxiliary cell, some adjacent cortical cells and some older gonimoblasts results in a cavity which is lined by gonimoblast derivatives connected to surrounding nutritive and other vegetative cells. With expansion of the cavity, branched gonimoblast filaments grow centripetally and produce terminal or short chains of carposporangia that are released through distinct ostioles. In Amphiplexia, nutritive cells do not completely surround the auxiliary cell, and most gonimoblast filaments initially cover the interior surface of the pericarp rather than a cavity lined by specially produced nutritive cells. The genera are separated on wide differences in habit, vegetative cross section, carpogonial branches, gonimoblast orientation, carpospore morphology and mature cystocarp cross sections. The two African genera Ranavalona and Reinboldia appear on vegetative and certain reproductive grounds to be relatively primitive in the group, with possible links to the less reproductively complex family Solieriaceae. The most closely related genera within the Acrotylaceae, Acrotylus and Ranavalona, are also about the most geographically separated. The present-day distinctiveness, uncommonness and distribution of the genera of the Acrotylaceae perhaps suggest that it is a relict and isolated group.
Thallus
Gigartinales
Frond
Holdfast
Paleobotany
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Abstract The red seaweed Pyropia yezoensis is a marine crop of important economic value and is widely cultivated in the coastal areas of northern China. The current seedling-raising system relies on the germination of conchospores, a process not fast enough to meet the increasing demand from farmers. In this study, we developed a monospore-dependent seedling method based on the asexual reproduction of the Pyropia thallus. The Pyropia thallus was physically sectioned into small pieces (microthalli) that were cultivated at 15 °C. The algal cells in the microthalli became morphologically condensed, underwent cell division, and then developed into monospores on the 5th day. The monospores were able to attach to the seeding rope in 24 h and germinated into healthy thalli. To optimize the efficiency of monospore release, we tested the effect of temperature and the size and original positions of the microthalli as well as the age of the mother thallus. Microthalli with a size of 30–50 cells from the middle and apex of 21-day-old thalli cultivated at 15 ° C yielded the optimum production of monospores. Theoretically, in this thallus-to-thallus seeding strategy, 0.1 g of thallus could produce at least 10 7 monospores, with the same number of offspring thallus seedlings. Taking all of these advantages together, including the high efficiency, short time, low cost and easy operation, this physical sectioning method could serve as a promising seed source especially for new cultivars with superior traits in Pyropia farming and rapid replenishment of seedlings when thalli undergo disastrous diseases.
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