Developmental morphology of Sarcodia montagneana and S. grandifolia from New Zealand and a phylogeny of Sarcodia (Sarcodiaceae, Rhodophyta) based on rbcL sequence analysis

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Despite its widespread distribution in the Indo-West Pacific Ocean, Sarcodia is one of the least understood genera among the red algae. Samples investigated from different parts of the Indo-West Pacific Ocean were well separated phylogenetically, based on rbcL base pair distances, and probably represent separate species. In this report we investigate the developmental morphology of two species from New Zealand: the type species, Sarcodia montagneana, and S. grandifolia (including S. ‘flabellata’). Molecular studies indicate that S. montagneana is restricted to the north-eastern part of the North Island and that S. grandifolia occurs from Wellington southwards as far as the Snares Islands. Thalli are multiaxial and consist of three primary layers: a surface layer of uninucleate cells, a cortex of five or six layers of polygonal multinucleate cells, and a medulla of multinucleate stellate cells. Secondary rhizoidal filaments are frequent to abundant in the medulla. Spermatangia occur in chains and release spermatia through a pore. The female reproductive system is procarpic and consists of a supporting cell that bears two side branches and a one-celled terminal carpogonium. The auxiliary cell is the basal cell of one of the side branches and is undifferentiated prior to fertilization. After presumed fertilization, the carpogonium separates into a terminal cell and a subterminal hypogynous cell that fuses with the auxiliary cell and deposits in it a single nucleus. The auxiliary cell cuts off a gonimoblast initial obliquely that first forms a short linear chain of gonimoblast cells. Cystocarp formation proceeds rapidly with the outward development of linear files derived from surface cells that differentiate into a terminal ostiole and inner and outer pericarp layers separated by a central cavity. The mature gonimoblasts consist of an inner gonimoblast reticulum of laterally fused cells that attach secondarily to outer cells of the inner pericarp and outer gonimoblast filaments that terminate in short chains of carposporangia. Tetrasporangia are zonately divided and are scattered over the thallus surface with new initials formed continuously. The morphological and molecular observations reported here contrast sharply with those of previous studies and are largely new to the Sarcodia literature ​
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